MX2007005755A

MX2007005755A - Cytokinin-sensing histidine kinases and methods of use

Info

Publication number: MX2007005755A
Application number: MXMX/A/2007/005755A
Authority: MX
Inventors: J Meister Robert; Sivasankar Shoba
Original assignee: J Meister Robert; Pioneer Hibred International Inc; Sivasankar Shoba
Priority date: 2004-11-12
Filing date: 2007-05-11
Publication date: 2008-10-03

Abstract

Isolated polynucleotides that encode cytokinin-sensing histidine kinase polypeptides, and the encoded polypeptides, are described. Expression cassettes comprising the polynucleotides of the invention and plants and plant cells that are transformed with the polynucleotides are described. Methods of using the cytokinin-sensing histidine kinase polypeptides and polynucleotides to modulate histidine kinase activity and/or histidine kinase levels in plants and plant cells are further described.

Description

HISTIDINE KINASES WITH SCIENCE ACTIVITY OF CYTOQUININE AND METHODS OF USE THEREOF This application claims priority, and incorporates in this by way of reference, the US Provisional Patent Applications. No.: 60 / 627,394, filed on November 12, 2004, and 60 / 706,787, filed August 9, 2005. FIELD OF THE INVENTION The invention is directed to the field of plant molecular biology, in particular to molecules of nucleic acid encoding corn histidine kinases and methods of using them. BACKGROUND OF THE INVENTION Plants and other organisms employ signal transduction systems to sense environmental and hormonal stimuli and to respond to them through altered cellular processes through changes in the amount or activity of cascades of genetic products. Reversible phosphorylation of proteins is a key mechanism for intracellular signal transduction in eukaryotic and prokaryotic cells (Urao et al (2000) Trends Plant Sci. 5: 67-74). Said mechanisms of reversible protein phosphorylation comprise the protein kinases. Protein kinases known for their participation in signal transduction are classified into three groups: serine / threonine protein kinases, tyrosine protein kinases and histidine protein kinases (Sakakibara et al (2000) Plant Mol. Biol. 42: 273-278) . Although the specific function of histidine protein kinases (also called "histidine kinases" in the present) is only beginning to be known in plants, it is known that histidine kinases of bacteria perform important functions in the sensing and transduction activity of various stimuli. extracellular (Urao et al. (2001) Science's STKE doi: 10.1 26 / stke.2001 .109.re18). The signal transduction systems to which the histidine kinases are related are known as two-component signaling systems or His-Asp fosforele [phosphorelay] systems (Sakakibara et al. (2000) Plant Mol. Biol. 42: 273-278 ). Two-component plant systems typically consist of three domains: a domain with sensing activity (hybrid histidine kinase), a histidine containing a phosphotransfer domain and a receptor domain (response regulator) (Sakakibara et al., 2000) Plant Mol. Biol. 42: 273-278; Grefen and Harter (2004) Plant (First in line) doi: 10.1007 / s00425-004-1316-4). In addition to a histidine kinase domain and an invariant histidine residue that is autophosphorylated, hybrid histidine kinases include a receptor domain usually at the terminal COOH end having a conserved aspartate residue (Grefen and Harter (2004) Plant (First inline) doi: 0.1007 / s00425-004-1316-4). Instead of transferring the phosphoryl group directly to the response regulator, it is first transferred from the autophosphorylated histidine residue to the conserved aspartate residue of the receptor domain (Grefen and Harter (2004) Plant (First in line) doi: 10.1007 / s00425-004-1316- 4). In plants, histidine kinases are related to the two-component systems involved in osmosensory activity and the perception of plant hormones ethylene and cytokinin (Urao et al. (2001) Science's STKE doi: 10.1 126 / stke.2001 .109 re18). According to the prevalence of genes encoding bacterial-type two-component histidine kinases in the genome of the model plant, Arabidopsis thaliana, two-component bacterial-type histidine kinases are expected to be related to signal transduction systems of various environmental and hormonal stimuli. They have cloned histidine plant kinases including Arabidopsis thaliana (Chang et al. (1993) Science 262: 539-544; Hua ef al. (1995) Science 269: 1712-1714; Kakimoto (1996) Science 274: 982-985; Hua et. al. (1998) Plant Cell 10: 1321-1332; Sakai et al. (1998) Proc. Nati, Acad. Sci. USA 95: 5812-5817), tomato (Payton et al. (1996) Plant Mol. Biol. 31: 1227-1231; Lashbrook et al. (1998) Plant J. 15: 243-252), Rumex palustris (Vriezen et al., 1997) Plant J. 1 1: 1265-1271) and tobacco (Zhang et al., (2004) Plant Physiol. 136: 2971 -2981). Among the plant histidine kinases, those of Arabidopsis thaliana are the most investigated to date. Sequence analysis of the Arabidopsis thaliana genome has revealed that there are at least sixteen genes encoding putative histidine kinases (Hwang et al (2002) Plant Physiol. 129: 500-515). Grefen and Harter ((2004) Plant (First in line) doi: 10.1007 / s00425-004-1316-40) has indicated that the sequence analysis of the entire Arabidopsis genome reveals the presence of eight canonical histidine kinases. Among the eight canonical histidine kinases of Arabidopsis, five (ETR1, ETR2, EIN4, ERS1 and ERS2) function as ethylene receptors and one (CRE1) acts as a cytokinin receptor (Urao et al. (2001) Science's STKE doi: 10.1 126 / stke.2001 .109, re18). There are two additional Arabidopsis histidine kinases, CKI1 and CKI2, which are also putative cytokinin receptors according to the genetic analyzes (Urao et al (2000) Trends Plant Sci. 5: 67-74). Arabidopsis histidine kinase homologs are divided into three distinct families: ethylene receptors, phytochrome photoreceptors and the AHK family, which includes a cytokinin receptor (CRE1 / AHK4 / WOL1) and a putative osmosensor receptor (AtHK1) (Hwang et al (2002) Plant Physiol. 129: 500-515). Several publications refer to the putative in vivo role of CKI2 (AtCKI2) of Arabidopsis in the transduction of cytokinin signals (Kakimoto, 1996, Grefen and Harter, 2004, Higuchi et al., 2004). This histidine kinase clearly lacks the SENSORY extracellular domain ASSOCIATED cyclases / HISTIDINE KINASE [cyclases / Histidine kinases ASSOCIA TED SENSORY Extracellular] (CHASE) binding cytokinin (Anantharaman and Aravind, 2001; Mougel and Zhulin., 2001; Yamada et al, 2001). The data described in said publication indicate that AtCKI2 functions as a single intracellular histidine kinase. The carboxyl terminus of the AtCKI2 protein can interact with the PHOSPHOTRANSFERENCE proteins of ARABIDOPSIS HISTIDINE as well as with a protein kinase not previously described. The tissue analyzes of callus from transgenic plants and CKI2 mutants indicate that the protein can positively modulate growth in response to cytokinins in a manner similar to AHK3. As the global human population continues to increase, new strategies are needed to improve plants of agronomic interest in order to meet the demands of increased food production. A better understanding of the components of signal transduction systems will help in the development of new strategies to improve crop plants of agronomic interest. COMPENDIUM OF THE INVENTION The present invention provides compositions and methods for modulating signal transduction systems in plants. The compositions comprise isolated polynucleotides encoding histidine kinases and isolated polypeptides comprising histidine kinases. The selected isolated polynucleotides of the invention comprise a nucleotide sequence selected from the group consisting of: SEQ ID N °: 1, 3, 4, 6, 7, 9, 13, 15, 16, 18, 26, 28, 30 and 32; the nucleotide sequences that encode the amino acid sequences that are show in SEQ ID N °: 2, 5, 8, 14, 17, 23, 27 and 31; and fragments and vanishing of them. Also, isolated polypeptides selected from the invention comprise an amino acid sequence selected from the group consisting of: SEQ ID N °: 2, 5, 8, 14, 17, 23, 27 and 31; the amino acid sequences encoded by the nucleotide sequences shown in SEQ ID N °: 1, 3, 4, 6, 7, 9, 13, 15, 16, 18, 26, 28, 30 and 32; and fragments and variants thereof. The present invention also provides expression cassettes and plants, plant tissues, plant cells and transformed seeds. The expression cassettes comprise at least one histidine kinase polynucleotide of the invention operably linked to a promoter that directs expression in a plant or cell. The plants, plant tissues, plant cells and transformed seeds comprise at least one histidine kinase polynucleotide of the invention operably linked to a promoter that directs expression in a plant or a cell thereof. In one example of the invention, the histidine kinase polynucleotide of the invention is stably incorporated into the genome of plants, plant tissues, plant cells or transformed seeds. The present invention provides a method for increasing the activity of a polypeptide in a plant comprising providing in the plant a histidine kinase polypeptide of the invention. In one example, the method comprises introducing into the plant or in at least one cell thereof a histidine kinase polynucleotide of the invention. If desired, the polynucleotide can be stably incorporated into the genome of the plant. In another example, the method comprises introducing the histidine kinase polypeptide into a plant or at least one cell thereof. The plants produced by this method present a Higher level of histidine kinase activity relative to a plant to which a histidine kinase polypeptide was not provided. The present invention provides a method for modulating the level of a polypeptide in a plant comprising introducing into a plant a polynucleotide comprising a nucleotide sequence encoding a histidine kinase of the invention. The polynucleotide may further comprise a promoter operably linked to the nucleotide sequence encoding histidine kinase., wherein said nucleotide sequence can be oriented in the sense of the reading or antisense framework. According to the desired result, the method can be used to increase or decrease the level of a histidine kinase polypeptide in a plant or part of a plant. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is an alignment of histidine kinases of hybrid type receptors. Homologs of sequences from CKI2 of Zea mays (ZmCKI2, SEQ ID No. 8), Oryza sativum (OsCKI2, SEQ ID No. 23) and Arabidopsis thaliana (AtCKI2, SEQ ID No. 14) were aligned with cytokinin receptors putatives of Zea mays (ZmHK1, SEQ ID N °: 22; ZmHK2, SEQ ID N °: 5; ZmHK3, SEQ ID N °: 31; and ZmCREI, SEQ ID N °: 1) and Arabidopsis thaliana (AtCREI, SEQ ID N °: 21, AtAHK2, SEQ ID N °: 19, and AtAHK3, SEQ ID N °: 20) using a BLOSUM62 matrix from CLUSTALW software. The ZmCREI sequence is a full length sequence based on a commercial EST clone and a sequence derived from a BAC test. The conserved residues of histidine kinase (overlay) and the response regulatory domains (double overlay) are highlighted (Slides 3-5) and the putative phosphorylation sites are indicated with an asterisk (Hwang et al. (2002) Plant Physiol. 129: 500-515). The amino terminal regions of the CKI2 homologs (identical residues highlighted and in italics; Laminae 1-3) contain a nuclear type PAS domain (dot underlining) (Taylor and Zhulin (1999) Microbium, Mol .. Biol. Rev. 63-479-506) adjacent to a putative helical alpha region. In contrast, putative cytokinin receptors contain the hormone-binding CHASE domain (Anatharaman and Aravind, (2001) Trends Biochem, Sci. 26: 579-582) (identical highlighted and underlined residues, Slides 1-3). The non-conserved regions (inverted text) include the amino terminal end of the proteins that contain the CHASE domain, the residues flanked by the N and G1 boxes of the histidine kinase domain and the residues between the conserved histidine kinase domains and response regulator . Figure 2 is an alignment with ClustalW of the amino acid sequences of CKI2 from Arabidopsis and rice. The identical residues are shaded and the putative phosphorylated residues are shown as inverted text. AT, Arabidopsis thaliana; OS, Oryza sativum. Figure 3 shows the putative functional domains of AtCKI2. AtCKI2 contains signature residues from both the histidine kinase (A) and regulatory response (B) domains (the identical residues in at least four sequences are shown as inverted text), including the histidine and aspartate (asterisk) phosphorylated residues. (C) The amino terminal end of CKI2 has a sequence identity region with the signature residues of the nuclear PAS domain (asterisk). There are three adjacent regions (dot overlay) with a motif of a repeating hydrophobic residue (highlighted in gray). AT, Arabidopsis thaliana; OS, Oryza sativum; SC, Saccharomyces cerevisiae; two dots represent a variable amount of amino acids that were omitted for purposes of clarity; the H, N, G1, F and G2 motifs of histidine kinases and four motifs of regulators of responses have already been described previously (Stock et al. , 2000). The sequence of AtETRI shown is from NCBI, Accession No. AAA 70047 (SEQ ID N °: 33). The sequence ScSLN I shown is from NCBI, Accession No. CAA 86131 (SEQ ID N °: 34). Figure 4. Arabidopsis histidine kinase insertion mutants. The genomic insertion site of the left border sequence of the T-DNA was determined for (A) cki2-2 (SEQ ID NO: 35), (B) ahk3-4 (SEQ ID NO: 20), and ( C) ahk1-1 (SEQ ID N °: 25). In ck2-2 and ahk3-4, the in-frame translation product of the left border sequence, with a point representing the termination codon, is shown as inverted text. The insert cki2-2 is located between the motifs II and III of the domain of the response regulator. The ahk3-4 insertion is located within the G2 box of the histidine kinase domain and the ahk1-1 insertion is adjacent to the G2 box, located between the histidine kinase and response regulator domains. Figure 5. Phylogenetic tree of Arabidopsis histidine kinases and maize. The names of the boxes represent the new maize sequences identified. The alignment was made using a BLOSUM matrix of CLUSTALW software. LIST OF SEQUENCES The nucleotide and amino acid sequences listed in the attached sequence listing are shown using the standard letter abbreviations for nucleotide bases and the three letter code for amino acids. For the nucleotide sequences the standard convention was applied starting at the 5 'end of the sequence and moving towards the 3' end (ie from left to right on each line). Only one strand of each nucleic acid sequence is shown, but the complementary strand is considered to be included with the reference to the strand shown. For the amino acid sequences, apply the standard convention of starting at the amino terminus of the sequence and moving towards the carboxyl terminus (ie, from left to right on each line). The coding sequences described and / or referenced herein may include, or not, a stop codon. If desired, a stop codon can be added to any coding sequence. Such termination codons include, for example, TAA, TAG and TGA. In SEQ ID NO: 1 the nucleotide sequence encoding the corn ZmCREI protein is shown. The coding sequence of the protein comprises from nucleotide 2901. In SEQ ID NO: 2 the amino acid sequence of ZmCREI which is encoded by SEQ ID No. 1 is shown. In SEQ ID NO: 3 the nucleotide sequence for the ZmHK3 coding region of SEQ ID No. 1 is shown. Nucleotides 1 -2901 of SEQ ID NO: 3 correspond to nucleotides 1 -2901 of SEQ ID NO: 1. In SEQ ID N °: 4 the nucleotide sequence encoding the corn ZmHK2 protein is shown. The coding sequence of the protein comprises nucleotides 1-3021. In SEQ ID No. 5 the amino acid sequence of ZmHK2 which is encoded by SEQ ID No. 4 is shown. In SEQ ID No. 6 the nucleotide sequence for the ZmHK2 coding region of SEQ ID N °: 1. Nucleotides 1 -3021 of SEQ ID NO: 6 correspond to nucleotides 1 -3021 of SEQ ID N °: 4. In SEQ ID N °: 7 the nucleotide sequence encoding the corn protein ZmCKI2 is shown . The coding sequence of the protein comprises nucleotides 1-2895.

In SEQ ID NO: 8 the amino acid sequence of ZmCKI2 which is encoded by SEQ ID No. 7 is shown. In SEQ ID No. 9 the nucleotide sequence for the coding region of ZmCKI2 is shown. SEQ ID N °: 7. Nucleotides 1 -2895 of SEQ ID N °: 9 correspond to nucleotides 1 -2895 of SEQ ID N °: 7. In SEQ ID N °: 10 the sequence of nucleotides encoding the partial length coding sequence of the corn ZmCREI protein. In SEQ No.:1 1 the amino acid sequence of ZmCREI which is encoded by SEQ ID No. 0 is shown. In SEQ No.: 12 the nucleotide sequence encoding the partial length amino acid sequence is shown of ZmCREI of SEQ ID N °: 1 1. Nucleotides 1-1788 of SEQ ID NO: 12 correspond to nucleotides 3-1790 of SEQ ID NO: 10. In SEQ No.: 13 the nucleotide sequence encoding AtCKI2 (NCBI, Access No. AAZ98829). In SEQ No.: 14 the amino acid sequence of AtCKI2 which is encoded by SEQ ID No. 13 is shown. In SEQ No.: 15 the nucleotide sequence for the AtCKI2 coding region of the SEQ is shown. ID N °: 13. Nucleotides 1 to 2769 of SEQ ID N °: 15 correspond to nucleotides 378-3146 of SEQ ID N °: 1 3. SEQ N °: 16 shows the nucleotide sequence that encodes AtAPK3. In SEQ No.: 17 the amino acid sequence of AtAPK3 which is encoded by SEQ ID No. 6 is shown.

In SEQ No.:18 the nucleotide sequence for the AtAPK3 coding region of SEQ ID NO: 16 is shown. Nucleotides 1 to 1428 of SEQ ID NO: 18 correspond to nucleotides 1 to 1428 of SEQ ID N °: 16. SEQ N °: 19 shows the amino acid sequence of AtAHK2. In SEQ No.:20 the amino acid sequence of AtAHK3 is shown. In SEQ No.: 21 the amino acid sequence of AtCREI is shown. In SEQ No.:22 the amino acid sequence of ZmHK1 is shown. In SEQ No.:23 the amino acid sequence of OsCKI2 is shown. In SEQ No.: 24 the amino acid sequence of AtCKM is shown. In SEQ No.:25 the amino acid sequence of AtHK1 is shown. In SEQ No.:26 the nucleotide sequence encoding ZmCKH is shown. In SEQ No.:27 the amino acid sequence that is encoded by SEQ ID No. 26 is shown. In SEQ No. 28, the nucleotide sequence for the ZmCKM coding region of SEQ ID N is shown. °: 26. Nucleotides 1 to 3180 of SEQ ID NO: 28 correspond to nucleotides 1 to 3180 of SEQ ID NO: 26. In SEQ No.: 29 a promoter sequence of AtCKI2 is shown. In SEQ No.:30 the nucleotide sequence encoding ZmHK3 is shown. In SEQ No.:31 the amino acid sequence is shown which is encoded by SEQ ID NO: 30. In SEQ No.: 32 the nucleotide sequence for the ZmHK3 coding region of SEQ ID N is shown. °: 30. Nucleotides 1 to 3606 of SEQ ID NO: 32 correspond to nucleotides 1 to 3606 of SEQ ID NO: 30.

In SEQ No.: 33 the amino acid sequence of AtETRI (AAA 70047) is shown. In SEQ No.: 34 the amino acid sequence of ScSLNI (CAA 86131) is shown. In SEQ No.:35 the insertion mutant ck2-2 of Figure 4A is shown. DETAILED DESCRIPTION OF THE INVENTION Polynucleotides encoding histidine kinases, the histidine kinase polypeptides encoded by them and methods for using same are provided. It is known that said histidine kinases, also called histidine-protein kinases, are related to two-component systems of signal transduction in plants and other eukaryotic organisms and in prokaryotes. In bacteria, histidine kinases are related to signal transduction in response to extracellular signals including chemotactic factors, changes in osmolarity and nutrient deficiency (Urao et al (2000) Trends Plant Sci. 5: 67-74). In plants, it is known that histidine kinases are related to osmosensory activity, the perception of ethylene and cytokinin signaling (Sakakibara et al., (2000) Plant Mol. Biol. 42: 273-278.; Urao er al. (2000) Trends Plant Sci. 5: 67-74). Accordingly, the histidine kinase polynucleotides and polypeptides of the present invention will be useful in methods of modulating the signal transduction pathways in plants to alter the responses of plants, in particular of crop plants of agronomic interest, to environmental and / or hormonal stimuli. The compositions of the invention include polynucleotides and corn histidine kinase polypeptides related to the two-component systems of signal transduction in plants. In particular, the present invention provides isolated polynucleotides comprising nucleotide sequences encoding the amino acid sequences shown in SEQ ID NOS: 2, 5, 8, 14, 17, 27 and 31, including the polynucleotides of SEQ ID NO: 3 , 4, 6, 7, 9, 13, 15, 16, 18, 26, 28, 30 and 32; the polypeptides encoded therein; the amino acid sequence of SEQ ID NO: 23; and fragments and variants thereof. The invention encompasses isolated or substantially purified polynucleotide or protein compositions. An "isolated" or "purified" polynucleotide or protein, or a biologically active portion thereof, is substantially or essentially free of the components that usually accompany or interact with the polynucleotide or the protein as they are in their natural environment. Accordingly, an isolated or purified polynucleotide or protein is substantially free of other cellular material, or culture medium when produced by recombinant techniques, or substantially free of chemical precursors or other chemical substances when chemically synthesized. Preferably, an "isolated" polynucleotide is free of the sequences (preferably the sequences encoding proteins) that usually flank the polynucleotides (i.e., sequences located at the 5 'and 3' ends of the polynucleotide) in the genomic DNA of the organism of which derives the nucleic acid. For example, in various examples, the isolated polynucleotide may contain less than about 5 kb, 4 kb, 3 kb, 2 kb, 1 kb, 0.5 kb or about 0.1 kb of the flanking nucleotide sequences that usually flank the polynucleotide in the genomic DNA of the cell from which the polynucleotide derives. The protein that is substantially free of cellular material includes preparations of proteins that possess less than 30%, 20%, 10%, 5% or 1% (by dry weight) of contaminating proteins. When the protein of the invention or a biologically active portion thereof is produced recombinantly, the culture medium preferably represents less than 30%, 20%, 10%, 5% or 1% (by dry weight) of approximately chemical precursors or of chemical substances that are not the proteins of interest. The use herein of the terms "polynucleotide", "polynucleotide molecule", "nucleic acid molecule", "nucleotide sequence" and the like is not intended to limit the present invention to molecules of polynucleotides, polynucleotides, nucleic acid molecules and nucleotide sequences comprising DNA. It will be understood by those skilled in the art that polynucleotides and oligonucleotides composed of ribonucleotides and combinations of ribonucleotides and deoxyribonucleotides can also be employed in the methods described herein. Accordingly, the present invention encompasses all polynucleotide constructs that can be employed in the methods of the present invention to transform plants including, by way of example, those comprising deoxyribonucleotides, ribonucleotides and combinations thereof. Said deoxyribonucleotides and ribonucleotides include both natural and synthetic analogues. The polynucleotides of the invention also encompass all forms of nucleotide constructions including, by way of example, single chain forms, double chain forms, hairpins, stem-and-loop structures and the like. The fragments and variants of the polynucleotides and the described proteins encoded by them are also included in the present invention. The term "fragment" means a portion of the polynucleotide sequence or a portion of the amino acid sequence and hence the protein encoded thereby. Fragments of a polynucleotide can encode protein fragments that retain the biological activity of the native protein and thus may exhibit histidine kinase activity. As an alternative, fragments of polynucleotides that are useful as hybridization probes generally do not encode protein fragments that retain biological activity. Fragments of a nucleotide sequence can be in a range of at least about 20 nucleotides, about 50 nucleotides, about 100 nucleotides, and up to the full length polynucleotide sequence encoding the proteins of the invention. A fragment of a histidine kinase polynucleotide encoding a biologically active portion of a histidine kinase protein of the invention will encode at least 15, 25, 30, 50, 100, 50, 200, 250, 300, 350, 400, 450, 500 , 550, 600, 650, 700, 800, 900, 1, 000, 1, 100 or 1,200 contiguous amino acids, or up to the total amount of amino acids present in a histidine kinase protein of the invention (eg, 966, 1007 and 965, 918, 476, 968, 1059 and 1201 amino acids for SEQ ID N °: 2, 5, 8, 14, 17, 23, 27 and 31, respectively). In general it is not necessary that fragments of histidine kinase polynucleotides that are useful as hybridization probes or primers for PCR encode a biologically active portion of a histidine kinase protein. Accordingly, a fragment of a histidine kinase polynucleotide can encode a biologically active portion of a histidine kinase protein or it can be a fragment that can be used as a hybridization probe or a primer for PCR using the methods that will be described below. A biologically active portion of a histidine kinase protein can be prepared by isolating a portion of one of the histidine kinase polynucleotides of the invention, expressing the encoded portion of the histidine kinase protein (eg, by recombinant expression in vitro) and evaluating the activity of the encoded portion of the histidine kinase protein. Polynucleotides that are fragments of a histidine kinase nucleotide sequence comprise at least 16, 20, 50, 75, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400, 1,500, 1,750, 2,000, 2,250, 2,500, 3,000, 4,000 or 4,500 nucleotides or up to the amount of nucleotides present in a polynucleotide in length complete of the histidine kinase nucleotide sequence described herein (e.g., 2901, 2901, 3021, 3021, 3021, 2895, 2895, 2895, 3291, 2754, 1431, 1428, 3240, 3180, 3606 and 3,606 nucleotides for SEQ ID N °: 1, 3, 4, 6, 7, 9, 13, 15, 16, 18, 26, 28, 30 and 32, respectively). The term "variants" means substantially similar sequences. For polynucleotides, a variant comprises the deletion and / or addition of one or more nucleotides at one or more sites within the native polynucleotide and / or the substitution of one or more nucleotides at one or more sites on said native polynucleotide. As used herein, a "native" polynucleotide or polypeptide comprises a nucleotide sequence or natural amino acid sequence, respectively. For polynucleotides, conservative variants include those sequences which, due to the degeneracy of the genetic code, encode the amino acid sequence of one of the histidine kinase polypeptides of the invention. Natural allelic variants such as the ones just mentioned can be identified using well-known molecular biology techniques, such as, for example, the polymerase chain reaction (PCR) and hybridization techniques that will be described later. Vatants of polynucleotides also include polynucleotides derived by synthesis, such as those generated, for example, using site-directed mutagenesis with the histidine kinase protein of the invention. In general, the vanantes of a polynucleotide Particular of the invention will have at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more of sequence identity with said particular polynucleotide, determined with the programs and sequence alignment parameters described elsewhere herein. Variants of a particular polynucleotide of the invention (ie, the reference polynucleotide) can also be evaluated by comparing the percentage of sequence identity between the polypeptide encoded by a polynucleotide variant and the polypeptide encoded by the reference polynucleotide. Then, for example, an isolated polynucleotide encoding a polypeptide with a given percentage of sequence identity is described with the polypeptide of at least one sequence selected from the group consisting of SEQ ID NOS: 2, 5, 8, 14, 17 , 23, 27 and 31. The percentage of sequence identity between any two polypeptides can be calculated using the sequence alignment programs and parameters described elsewhere in this document. When evaluating any given pair of polynucleotides of the invention by comparing the percentage of sequence identity shared by the two polypeptides encoded by it, said percentage of sequence identity between the two encoded polypeptides is at least about 60%, 65% , 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more of sequence identity. A "variant" of protein means a protein derived from the native protein by deletion or addition of one or more amino acids at one or more sites on the native protein and / or the substitution of one or more amino acids at one or more sites on the protein native The variants of the proteins comprised by the present invention are biologically active, that is, they still possess the biological activity desired of the native protein, in this case, the histidine kinase activity described herein. Said variants may be the result of, for example, genetic polymorphisms or human intervention. The biologically active variants of the native histidine kinase protein of the invention will have at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more of sequence identity with the amino acid sequence of the native protein determined with the sequence alignment programs and parameters described elsewhere herein. A biologically active variant of a protein of the invention may differ from said protein by as little as 1-15 amino acid residues, as little as 1-10, such as 6-10, as little as 5, as little as 4.3. , 2 or even 1 amino acid residue. The proteins of the invention can be altered in various ways, including substitutions, deletions, truncations and amino acid insertions. Methods for such manipulations are generally known in the art. For example, variants of the amino acid sequence and fragments of the histidine kinase proteins can be prepared by mutations in the DNA. Methods for carrying out mutagenesis and alterations of polynucleotides are well known in the art. See, for example, Kunkel (1985) Proc. Nati Acad. HE/. USA UU 82: 488-492; Kunkel ef al. (1987) Methods in Enzymol. 154: 367-382; U.S. Patent No.: 4,873,192; Walker and Gaastra, eds. (1983) Techniques in Molecular Biology (MacMillan Publishing Company, New York) and the references cited therein. The guidelines for making substitutions of appropriate amino acids that do not affect the biological activity of the protein of interest can be consulted in Dayhoff's model ef el. (1978) Atlas of Protein Sequence and Structure (Nat.

Biomed. Res. Found., Washington, D.C.), incorporated herein by reference. Conservative substitutions, such as the exchange of one amino acid for another with similar properties, are optimal. Accordingly, the genes and polynucleotides of the invention include both the natural sequences and the mutant forms. In the same way, the proteins of the invention encompass both natural proteins and the variations and modified forms thereof. Said variants continue to retain the desired histidine kinase activity. Obviously, mutations that will be made in the DNA encoding the variants should not place the sequence outside the reading frame and, preferably, will not create complementary regions that could produce a secondary mRNA structure. See, EP Patent Application Publication No. 75,444. Deletions, insertions and substitutions of the protein sequences comprised herein can not be expected to produce radical changes in the characteristics of the proteins. However, when it is difficult to predict the exact effect of substitution, deletion or insertion before producing it, the skilled artisan will understand that the effect will be evaluated by means of routine monitoring tests. That is, the activity can be evaluated by histidine kinase activity assays. See, for example, Posas et al. (1 996) Cell 86: 865-875, incorporated herein by reference in its entirety. More recently, Zhang et al. have presented in vitro demonstrations of histidine kinase activity, 2004 (Plant Physiol. 36: 2971-281), incorporated herein by reference. Since the function of the yeast SLN1 protein as a histidine kinase is now unambiguously established, histidine kinase activity assays can also be performed by complementation of the sln 1 mutant yeast (Ueguchi et al. (2001) Plant Cell Physiol. 42: 231-235), incorporated herein by reference in its entirety. The polynucleotide and protein variants also encompass sequences and proteins derived from a mutagenic and recombinogenic procedure, such as DNA recombination / intermixing. With such a procedure one or more different coding sequences can be manipulated to create a new histidine kinase possessing the desired properties. In this manner, libraries of recombinant polynucleotides are generated from a population of related polynucleotide sequences comprising regions of sequence with a substantial sequence identity and which can be homologously recombined in vitro or in vivo. For example, using this approach, sequence motifs encoding the domain of interest can be recombined between the histidine kinase genes of the invention and other known histidine kinase genes in order to obtain a novel gene encoding a protein with improvements in the property of interest, such as a greater Km in the case of an enzyme. Strategies for such DNA intermixing are known in the art. See, for example, Stemmer (1994) Proc. Nati Acad. Sci. EE. UU 91: 10747-10751; Stemmer (1994) Nature 370: 389-391; Crameri ei al. (1997) Nature Biotech. 16: 436-438; Moore ef al. (1997) J. Mol. Biol. 272: 336-347; Zhang ef al. (1997) Proc. Nati Acad. Sci. EE. UU 94: 4504-4509; Crameri et al. (1998) Nature 391: 288-291; and U.S. Pat. Nos .: 5,605,793 and 5,837,458. The polynucleotides of the invention can be used to isolate the corresponding sequences from other organisms, in particular other plants, more particularly other monocots. In this way, methods such as PCR, hybridization and the like can be used to identify said sequences on the basis of their sequence homology with the sequences that are described in the present. The isolated sequences on the basis of their sequence identity with the complete histidine quina sequence described herein or with variants and fragments thereof are encompassed by the present invention. Said sequences include sequences that are orthologous to the described sequences. The term "orthologs" refers to genes derived from a common ancestral gene that is found in different species as a result of speciation. Genes present in different species are considered orthologs when their nucleotide sequences and / or the protein sequences encoded by them share at least 60%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more of sequence identity. The functions of orthologs are often well conserved among species. Accordingly, isolated polynucleotides that encode a histidine kinase protein and that hybridize under severe conditions with at least one of the histidine kinase sequences described herein, or with variants or fragments thereof, are encompassed by the present invention. In a PCR approach, oligonucleotide primers can be designed for use in PCR reactions to amplify the corresponding DNA sequences from cDNA or genomic DNA extracted from any plant of interest. Methods for designing primers for PCR and PCR cloning are generally known in the art and are described in Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2nd ed., Cold Spring Harbor Laboratory Press, Plainview, New York). See also Innis et al., Eds. (1990) PCR Protocols: A Guide to Methods and Applications (Academic Press, New York); Innis and Gelfand, eds. (1995) PCR Strategies (Academic Press, New York); and Innis and Gelfand, eds. (1999) PCR Methods Manual (Academic Press, New York). Known PCR methods include, by way of example, methods employing paired primers, nested primers, specific individual primers, degenerate primers, gene-specific primers, vector-specific primers, partially mismatching primers and the like. In the hybridization techniques, all or part of a polynucleotide known as a probe is used which hybridizes selectively with other corresponding polynucleotides present in a population of cloned genomic DNA fragments or cDNA fragments (ie, genomic DNA or cDNA libraries). ) of a chosen body. Hybridization probes can be genomic DNA fragments, cDNA fragments, RNA fragments or other oligonucleotides and can be labeled with a detectable group, such as 32 P or any other detectable label. Thus, for example, hybridization probes can be prepared by labeling synthetic oligonucleotides on the basis of the histidine kinase polynucleotides of the invention. The methods of preparing probes for hybridization and for the construction of cDNA and genomic libraries are generally known in the art and are described in Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2nd ed., Cold Spring Harbor Laboratory Press, Plainview, New York). For example, the complete histidine kinase polynucleotide sequence described herein, or one or more portions thereof, can be used as a probe capable of specifically hybridizing with the corresponding histidine kinase messenger RNAs or polynucleotides. To obtain specific hybridization under various conditions, such probes include sequences that are unique among the histidine kinase polynucleotide sequences and are preferably at least about 10 nucleotides in length, and more preferably at least about 20 nucleotides in length. length. Said probes can be used to amplify the corresponding histidine kinase polynucleotides of the plant chosen by PCR. This technique can be used to isolate additional coding sequences from the desired plant or as a diagnostic assay to determine the presence of coding sequences in a plant. Hybridization techniques include screening with hybridization of plated DNA libraries (either plates or colonies, see, for example, Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2nd ed., Cold Spring Harbor Laboratory Press, Plainview , New York) Hybridization of such sequences can be carried out under severe conditions The terms "severe conditions" or "severe hybridization conditions" refer to conditions under which a probe will hybridize to its target sequence, up to a detectable degree greater than with other sequences (for example, at least 2 times with respect to the basal level) .Strict conditions depend on the sequence and will be different under different circumstances.The control of the severity of the hybridization conditions and / or of washing, allows to identify white sequences that are 100% complementary to the probe (probe homologs) .Alternatively, it is possible to adjust the conditions of severity ad to allow some mismatch in the sequences so that lower degrees of similarity are detected (heterologous probes). In general, a probe is less than about 1000 nucleotides in length, often less than 500 nucleotides in length. Typically, severe conditions will be those in which the concentration of salts is less than about 1.5 M Na ion, typically between 0.01 and 1.0 M approximately Na (or other salts) ion concentration. pH between 7.0 and 8.3 and the temperature is at least 30 ° C approximately for short probes (for example, between 10 and 50 nucleotides) and at least approximately 60 ° C for long probes (for example, more than 50 nucleotides). Severe conditions can also be achieved with the addition of destabilizing agents, such as formamide. Examples of low stringency conditions include hybridization with a buffer solution of 30 to 35% formamide, 1 M NaCl, 1% SDS (sodium dodecylsulfate) at 37 ° C and a 1X to 2X SSC wash (SSC 20X = NaCl 3.0 M / trisodium citrate 0.3 M) at 50-55 ° C. Examples of moderate severity conditions include hybridization in formamide 40 to 45%, NaCl 1 M, SDS 1% at 37 ° C and a wash in SSC 0.5X to 1 X at 55-60 ° C. Examples of high severity conditions include hybridization in 50% formamide, 1 M NaCl, 1% SDS at 37 ° C and a 0.1 X SSC wash at 60-65 ° C. Optionally, the wash buffer solutions may comprise SDS between about 0.1% and about 1%. The duration of the hybridization is generally less than about 24 hours, usually between about 4 and about 12 hours. The duration of the washing time will be enough time to reach equilibrium. Typically, the duration of the washing will be 1, 2, 5, 10, 1 5, 20, 30 or more minutes approximately. The specificity typically depends on the post-hybridization washes, the critical factors being the ionic strength and the temperature of the final wash solution. For DNA-DNA hybrids, the Tm can be approximated from the equation of Meinkoth and Wahl, Anal. Biochem. , 138: 267-284: Tm = 81, 5 ° C + 6.6 (log M) + 0.41 (% GC) - 0.61 (% form) - 500 / I; where M is the molarity of the monovalent cations,% GC is the percentage of guanosine and nucleotides of cytosine in the DNA,% form is the percentage of formamide in the hybridization solution and L is the length of the hybrid in base pairs. The Tm is the temperature (under defined ionic strength and pH) at which 50% of a complementary white sequence is hybridized with a perfectly matching probe. The Tm is reduced by approximately 1 ° C for every 1% of mismatch; therefore, it is possible to adjust the Tm, the hybridization and / or washing conditions to hybridize the sequences of the desired identity. For example, if you search for sequences with > 90% identity, the Tm can be decreased by 10 ° C. In general, severe conditions are selected to be about 5 ° C lower than the thermal melting point (Tm) for the specific sequence and its complement at a defined ionic strength and pH. However, very severe conditions may employ hybridization and / or a wash at 1, 2, 3 or 4 ° C less than the thermal melting point (Tm); moderately severe conditions may utilize hybridization and / or a wash at 6, 7, 8, 9 or 10 ° C less than the thermal melting point (Tm); Low stringency conditions can employ hybridization and / or a wash at 1 1, 12, 13, 14, 15 or 20 ° C less than the thermal melting point (Tm). Using the equation, the hybridization and washing compositions and the desired Tm, the skilled artisan will understand that variations in the severity of the hybridization and / or wash solutions are inherently described. If the degree of mismatch desired results in a Tm less than 45 ° C (aqueous solution) or 32 ° C (formamide solution) it is preferred to increase the concentration of SSC so that a higher temperature can be used. An extensive guide for nucleic acid hybridization can be found in Tijssen (1993) Laboratory Techniques in Biochemistry and Molecular Biology-Hybridization with Nucleic Acid Probes, Part I, Chapter 2 (Elsevier, New York); and Ausubel et al., eds. (1995) Current Protocols in Molecular Biology, chapter 2 (Greene Publishing and Wiley-lnterscience, New York). See Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2nd ed., Cold Spring Harbor Laboratory Press, Plainview, New York). The following terms are used to describe the sequence relationships between two or more polynucleotides or polypeptides: (a) "reference sequence", (b) "comparison window", (c) "sequence identity", (d) " percentage of sequence identity ". (a) As used herein, "reference sequence" is a defined sequence used as a basis for the comparison of sequences. A reference sequence may be a subset or the entirety of a specified sequence; for example, a segment of a genetic sequence or of full-length cDNA or the complete sequence of the gene or cDNA. (b) As used herein, a "comparison window" refers to a contiguous and specified segment of a polynucleotide sequence, wherein the polynucleotide sequence in the comparison window may comprise additions or deletions (i.e. mismatches or gaps) when compared to the reference sequence (which does not include additions or deletions) for optimal alignment of the two polynucleotides. In general, the comparison window is at least 20 contiguous nucleotides in length and, optionally, may be 30, 40, 50, 100 or more in length. Those skilled in the art will understand that in order to avoid a great similarity to the reference sequence due to the inclusion of mismatches in the polynucleotide sequence, a mismatch penalty is typically introduced and subtracted from the number of matches . Methods of sequence alignment for a comparison are well known in the art. Accordingly, the determination of the percent identity between any two sequences can be carried out using a mathematical algorithm. The non-limiting examples of these mathematical algorithms are: the algorithm of Myers and Milier (1988) CABIOS 4: 1 1-17; the local homology algorithm of Smith ef al. (1981) Adv. Appl. Math. 2: 482; the homology alignment algorithm of Needleman and Wunsch (1970) J. Mol. Biol. 48: 443-453; the similarity search method of Pearson and Lipman (1988) Proc. Nati Acad. Sci. 85: 2444-2448; the algorithm of Karlin and Altschul (1990) Proc. Nati Acad. Sci. USA 872264, modified as in Karlin and Altschul (1993) Proc. Nati Acad. Sci. EE. UU 90: 5873-5877 Computerized implementations of these mathematical algorithms can be used for sequence comparison in order to determine sequence identity. Such implementations include, by way of example: CLUSTAL in the PC / Gene program (available from Intelligenetics, Mountain View, California); including CLUSTALV and CLUSTALW; the ALIGN program (Version 2.0) and GAP, BESTFIT, BLAST, FASTA and TFASTA in the Wisconsin Genetics Software Package, Version 10 (available from Accelrys Inc., 9685 Scranton Road, San Diego, California, USA). The alignments used by these programs can be made using the default parameters. The CLUSTAL program is very well described by Higgins et al., (1988) Gene 73: 237-244 (1988); Higgins ef al. (1989) CABIOS 5: 151-153; Corpet ef al. (1988) Nucleic Acids Res. 16: 10881 -90; Huang ef al. (1992) CABIOS: 8: 155-65; and Pearson et al. (1994) Meth. Mol. Biol. 24: 307-331. The ALIGN program is based on the algorithm of Myers and Milier (1988) supra. A waste weight table PAM120, a restriction for mismatch of 12, and a mismatch restriction of 4 with the ALIGN program can be used when comparing amino acid sequences. The BLAST programs of Altschul et al (1990) J. Mol. Biol. 215: 403 are based on the algorithm of Karlin and Altschul (1990) supra. BLAST nucleotide searches can be performed with the BLASTN program, score = 100, word length = 1 2, to obtain the homologous nucleotide sequences of a nucleotide sequence encoding a protein of the invention. BLAST protein searches can be carried out with the BLASTX program, rating = 50, word length = 3, to obtain the homologous amino acid sequences of a protein or polypeptide of the invention. In order to obtain alignments with mismatches to make a comparison, Gapped BLAST (in BLAST 2.0) can be used as described in Altschul et al. (1997) Nucleic Acids Res. 25: 3389. Alternatively, PSI-BLAST (in BLAST 2.0) can be used to perform an iterated search to detect distant relationships between molecules. See, Altschul et al. (1997) supra. When using BLAST, Gapped BLAST, PSI-BLAST, the predetermined parameters of the respective programs can be used (for example, BLASTN for nucleotide sequences, BLASTX for proteins). See databases and programs offered online by the National Center for Biotechnology Information in the USA. of the National Institutes of Health [United States National Center for Biotechnology Information of the National Institutes of Health]. Alignments can also be made by manual inspection. GAP employs the algorithm of Needleman and Wunsch (1970) J. Mol. Biol. 48: 443-453, to find the alignment of two complete sequences that maximizes the number of matches and minimizes the number of mismatches. GAP takes into account all possible alignments and positions of matches and creates an alignment with the largest number of matching bases and the least number of mismatches. Allows the provision of a penalty limit for creation of mismatches and a penalty for the extension of the lack of coincidences, expressed in units of matching bases. GAP must obtain a profit with the penalty for creating mismatches in match amounts for each mismatch that it inserts. If a penalty is chosen for the extension of the mismatches greater than zero, GAP must also provide a gain for each inserted mismatch, whose length is the number of mismatches, with respect to the penalty for extension of the lack of coincidences. The default values for creating mismatches and the extent of mismatches in Version 10 of the GCG® Wisconsin Genetics software package (Accelrys, Inc., San Diego, California) for protein sequences are 8 and 2 , respectively. For nucleotide sequences, the default mismatch penalty is 50, while the default mismatch penalty is 3. The penalty for creation of mismatches and extension of mismatches can be expressed as an integer selected from the group of integers from 0 to 200. Thus, for example, the values of penalties for creation of mismatches and extension of mismatches may be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 or greater. Unless indicated otherwise, the identity / sequence similarity values provided in this document refer to the values obtained using GAP Version 10 with the following parameters:% identity and% similarity for a nucleotide sequence using a Weight of GAP of 50 (penalty for creation of gap) and a Weight of Length of 3 (penalty for gap extension); and the qualification matrix of nwsgapdna.cmp; % identity and% similarity for an amino acid sequence using a GAP Weight of 8 and a Weight of Length of 2, and the qualification matrix BLOSUM62; or any equivalent program thereof. GAP represents a member of the family of best alignments. This family can have many members, but no other member has a better quality. GAP shows four qualification values for the alignments: Quality, Relation, Identity and Similarity. Quality is the maximized metric to align the sequences. The Relationship is the quality divided by the number of bases in the shortest segment. Percentage Identity is the percentage of the symbols that actually match. Percentual Similarity is the percentage of symbols that are similar. The symbols that are crossed with respect to mismatches are not taken into account. A similarity is scored when the value of the qualification matrix for a pair of symbols is greater than or equal to 0.50, such as the similarity threshold. The scoring matrix used in Version 10 of the Wisconsin Genetics GCG software package is BLOSUM62 (see, Henikoff &Henikoff (1989) Proc. Nati, Acad. Sci. USA 89: 10915). (c) As used herein, "sequence identity" or "identity" in the context of two polynucleotide or polypeptide sequences refers to the residues in the two sequences that are the same when aligned by maximum correspondence in the specified comparison window. When the percentage of sequence identity is used with reference to proteins it will be understood that the positions of the residues that are not identical often differ by conservative substitutions of amino acids, where the amino acid residues are substituted by other amino acid residues with similar chemical properties ( example, loading or hydrophobicity) and therefore do not change the functional properties of the molecule. When the sequences differ by conservative substitutions, the percentage of sequence identity can be adjust upwards in order to correct the conservative nature of the substitution. It is said that the sequences that differ by said conservative substitutions possess "sequence similarity" or "similarity". The means for effecting this adjustment are well known to those skilled in the art. Typically, it comprises the qualification of a conservative substitution as a partial mismatch rather than a complete one, thereby increasing the percentage of sequence identity. Thus, for example, when an identical amino acid receives a rating of 1 and a non-conservative substitution receives a rating of zero, the conservative substitution receives a rating between zero and 1. The rating of conservative substitutions is calculated, for example, as implemented in the PC / GENE program (Intelligenetics, Mountain View, California). (d) As used herein, "percent sequence identity" means the value determined by comparison of two optimally aligned sequences in a comparison window, wherein the portion of the polynucleotide sequence in the comparison window may comprise additions or deletions (e.g., gaps) when compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of two sequences. The percentage is calculated by determining the number of positions in which the acid base or amino acid residue appears in both sequences to obtain the number of matching positions, dividing the number of matching positions by the total number of positions in the comparison window and multiplying the result by 100 to obtain the percentage of sequence identity. The histidine kinase polynucleotides of the invention can be provided in expression cassettes for expression in the plant of interest. The cassette will include 5 'and 3' regulatory sequences operatively linked to a histidine kinase polynucleotide of the invention. The term "operatively linked" refers to a functional linkage between two or more elements. For example, an operative linkage between a polynucleotide of interest and a regulatory sequence (i.e., a promoter) is a functional link that allows expression of the polynucleotide of interest. The elements operatively linked can be contiguous or non-contiguous. When used with reference to the binding of two protein coding regions, the term "operably linked" means that the coding regions are in the same reading frame. The cassette may also contain at least one additional gene that will be cotransformed in the organism. Alternatively, the gene or genes can be provided in multiple expression cassettes. Said expression cassette is provided with a plurality of restriction sites and / or recombination sites so that the insertion of the histidine kinase polynucleotide is under the regulation of the transcription of the regulatory regions. The expression cassette may also contain selectable marker genes. The expression cassette will include in the transcription direction 5'-3 ', a transcription and translation initiation region (i.e., a promoter), a histidine kinase polynucleotide of the invention and a terminator region of the invention. transcription and translation (ie, a termination region) functional in plants. The regulatory regions (ie, promoters, transcriptional regulatory regions and translation termination regions) and / or the histidine kinase polynucleotide of the invention may be native / analogous to the host cell or to each other. Alternatively, the regulatory regions and / or the histidine kinase polynucleotide of the invention can be heterologous to the host cell or to each other. As used herein, the term "heterologous" with reference to a sequence is a sequence originating from a strange species or, if it is of the same species, is substantially modified with respect to its native form in terms of composition and / or genomic locus by deliberate human intervention. For example, a promoter operably linked to a heterologous polynucleotide is from a species different from the species from which the polynucleotide is derived, or, if it is from the same species or an analogous species, one or both are substantially modified with respect to their shape and / or original genomic locus, or the promoter is not the native promoter for the operably linked polynucleotide. As used herein, a chimeric gene comprises a coding sequence operably linked to a transcription initiation region that is heterologous with respect to the coding sequence. Although it may be preferable to express the sequences using heterologous promoters, the native promoter sequences can be used. Said constructs will change the levels of histidine kinase expression in the plant or plant cell. Consequently, the phenotype of the plant or plant cell is altered. The termination region may be native with respect to the initiation region of the transcript, it may be native with respect to the histidine kinase polynucleotide operably linked of interest or with the histidine kinase promoter sequences, it may be native with respect to the host plant or it may be derived from another source (ie, foreign or heterologous) with respect to the promoter, the histidine kinase polynucleotide of interest, the host plant or any combination thereof. Suitable termination regions are available from the Ti plasmid of A. tumefaciens, such as the termination regions of octopine synthetase and nopaline synthetase. See also Guerineau I went to. (1991) Mol. Gen. Genet. 262: 141-144; Proudfoot (1991) Cell 64: 671-674; Sanfacon et al. (1991) Genes Dev. 5: 141-149; Mogen eí al. (1990) Plañí Cell 2: 1261-1272; Munroe et al. (1990) Gene 91: 151-158; You dance to the. (1989) Nucleic Acids Res. 17: 7891-7903; and Joshi went to. (1987) Nucleic Acids Res. 15: 9627-9639. When appropriate, the polynucleotides can be optimized for increased expression in the transformed plant. That is, the polynucleotides can be synthesized using the preferred plant codons for better expression. See, for example, Campbell and Gow (1990) Plant Physiol. 92: 1 -1 1 for a description of the preferred codon usage for the host. There are methods available in the art for synthesizing genes with preference for plants. See, for example, U.S. Pat. No. 5,380,831 and 5,436,391, and Murray et al. (1989) Nucleic Acids Res. 17: 477-498, incorporated herein by reference. Other sequence modifications that improve the expression of the gene in a host cell are known. Such modifications include the elimination of sequences encoding spurious polyadenylation signals, signals from exon-intron processing sites, transposon-like repeats and other well-characterized type sequences that may be deleterious to gene expression. The G-C content of the sequence can be adjusted in average levels for a given host cell, calculated with reference to known genes that are expressed in said host cell. When possible, the sequence will be modified in order to avoid the predicted secondary hairpin mRNA structures. The expression cassettes may also contain direct sequences '. Said guidelines sequences can improve translation. The guidelines of Translation are known in the art and include: the picornavirus guidelines, eg, EMCV directive (5 'non-coding region of encephalomyocarditis) (Elroy-Stein et al. (1989) Proc. Nati. Acad. Sci. , (86: 6126-6130), potivirus guidelines, for example, TEV (tobacco etch virus) directive (Gallie et al. (1995) Gene 165 (2): 233-238), the MDMV guideline (Virus in Mosaic Maize Dwarf) (Virology 154: 9-20), and the human immunoglobulin heavy chain binding protein (BiP) (Macejak et al. (1991) Nature, 353: untranslated guideline of the mRNA of the protein cover of the virus in alfalfa mosaic (AMV RNA 4) (Jobling et al., (1987) Nature, 325: 622-625), tobacco mosaic virus (TMV) guideline, (Gallie et al. (1989) in Molecular Biology of RNA, ed. Cech (Liss, New York), pp. 237-256), and guideline of mottled corn chlorotic virus (MCMV) (Lommel et al. (1991) Virology 81: 382- 385) See also Della-Cioppa et al. (198 7) Plant Physiol. 84: 965-968. Other known methods for improving translation may also be used, for example, patterns and the like. When the expression cassette is prepared, the various DNA fragments can be manipulated in order to provide the DNA sequences in the proper orientation and, as appropriate, in the proper reading frame. For this purpose, adapters or linkers can be used to join the DNA fragments or other manipulations can be used to provide convenient restriction sites, eliminate superfluous DNA, eliminate restriction sites or the like. For this purpose, in vitro mutagenesis, primer repair, restriction digestions, alignment, re-substitutions, for example transitions and transversions can be used. A number of promoters can be employed in the practice of the invention, including the native promoter of the polynucleotide sequence of interest. The promoters can be selected based on the desired result. That is, the nucleic acids can be combined with constitutive promoters, preferably by tissues or other promoters for their expression in plants. Such constitutive promoters include, for example, the nuclear promoter of Rsyn7 and other constitutive promoters as described in WO 99/43838 and in U.S. Pat. No.: 6,072,050; the nuclear promoter CaMV 35S (Odell et al (1,985) Nature 3) 3: 810-812); the rice actin promoter (McEIroy et al (1990) Plant Cell 2: 163-171); the ubiquitin promoter (Christensen et al (1989) Plant Mol. Biol. 12: 619-632 and Christensen et al. (1992) Plant Mol. Biol. 18: 675-689); the promoter pEMU (Last ef al. (1991) Theor, Appl. Genet, 81: 581-588); MAS (Velten er al. (1984) EMBO J. 3: 2723-2730); the ALS promoter (U.S. Patent No. 5,659,026), scpl (WO 97/47756, U.S. Patent No.: 6,555,673), the histone H2B promoter (U.S. Pat. N °: 6.177.61 1) and similar. Other constitutive promoters include, for example, those described in U.S. Pat. N °: 5,608,149; 5,608,144; 5,604.1 21; 5,569,597; 5,466,785; 5,399,680; 5,268,463; and 5,608,142 and 6,177.61. Promoters regulated by chemical compounds can be used to modulate the expression of a gene in a plant through the application of an exogenous chemical regulator. Depending on the objective to be achieved, the promoter can be a promoter inducible by chemical substances, when the application of the chemical induces the expression of the gene, or a promoter that can be repressed by chemical compounds when the application of the chemical represses the expression of the gene. Promoters inducible by chemical compounds are well known in the art and include, but are not limited to, the ln2-2 promoter of maize, which is activated by the herbicide benzenesulfonamide, the GST promoter of the corn that is activated by hydrophobic electrophilic compounds that are used as pre-emergent herbicides, and the PR-1 a promoter of tobacco, which is activated by salicylic acid. Other promoters regulated by chemical compounds of interest include promoters that respond to steroids (see, for example, glucocorticoid-inducible promoters in Schena et al (1991) Proc. Nati. Acad. Sc., USA 88: 10421 -10425 and McNellis et al (1998) Plant J. 14 (2): 247-257) and tetracycline-inducible and repressible promoters by tetracycline (see, for example, Gatz et al (1991) Mol. Gen. Genet. 227: 229-237, and Patents No.: 5,814,618 and 5,789,156), incorporated herein by reference. Promoters with preference for tissues can be used to obtain a higher expression of histidine kinase in a particular plant tissue. Promoters with preference for tissues include Yamamoto ef al. (1997) Plant J. 12 (2): 255-265; Kawamata et al. (1997) Plant Cell Physiol. 38 (7): 792-803; Hansen er al. (1997) Mol. Gen Genet. 254 (3): 337-343; Russell et al. (1997) Transgenic Res. 6 (2): 1 57-168; Rinehart et al. (1996) Plant Physiol. 1 12 (3): 1331-1341; Van Camp went to. (1996) Plant Physiol. 2 (2): 525-535; Canevascini eí al. (1996) Plant Physiol. 1 12 (2): 513-524; Yamamoto ef al. (1994) Plant Cell Physiol. 35 (5): 773-778; Lam (1994) Results Probl. Cell Differ. 20: 181 -196; Orozco et al. (1993) Plant Mol Biol. 23 (6): 1 129-1 138; Matsuoka er al. (1993) Proc. Nati Acad. Sci. EE. UU 90 (20): 9586-9590; and Guevara-Garcia et al. (1993) Plant J. 4 (3): 495-505. Said promoters can be modified, if necessary, to obtain a weak expression. Promoters with preference for sheets are known in the art. See, for example, Yamamoto er al. (1997) Plant J. 12 (2): 255-265; Kwon et al. (1994) Plant Physiol. 105: 357-67; Yamamoto et al. (1994) Plant Cell Physiol. 35 (5): 773-778; Gotor ef al. (1993) Plant J. 3: 509-18; Orozco et al. (1993) Plant Mol. Biol. 23 (6): 1 129-1 138; and Matsuoka ef al. (1993) Proc. Nati Acad. Sci. EE. UU 90 (20): 9586-9590 Root specific promoters are known and can be selected from all those that are available from the literature or can be isolated de novo from various compatible species. See, for example, Hire et al. (1992) Plant Mol. Biol. 20 (2): 207-218 (glutamine synthetase gene specific for soybean root); Keller and Baumgartner (1991) Plant Cell 3 (10): 1051 -1061 (root-specific control element in the GRP 1 .8 gene of beans); Sanger et al. (1990) Plant Mol. Biol. 14 (3): 433-443 (root specific promoter of the mannopine synthase (MAS) gene of Agrobacterium tumefaciens); and Miao et al. (1991) Plant Cell 3 (1): 1 1 -22 (full-length cDNA clone encoding cytosolic glutamine synthetase (GS), which is expressed in the roots and nodules of the roots of soy). See also, Bogusz et al. (1990) Plant Cell 2 (7): 633-641, where two root-specific promoters of hemoglobin genes were isolated from the non-legume nitrogen-fixing Parasponia andersonii and the non-legume nitrogen-fixing non-related Trema tomentosa. The promoters of these genes were linked to a β-glucuronidase reporter gene and introduced into the non-legume species Nicotiana tabacum and the legume species Lotus corniculatus, and in both cases the specific root promoter activity was retained. Leach and Aoyagi (1991) describe their analysis of the promoters of the high-expression root genes rolC and roID of Agrobacterium rhizogenes (see Plant Science (Limerick) 79 (1): 69-76). They concluded that the determinants of DNA enhancing and preferably tissue are dissociated in said promoters. Tee et al. (1989) used gene fusion with lacZ to demonstrate that the T-DNA gene of Agrobacterium encoding an octopine synthetase is especially active in the epidermis of the tip of the root and that the TR2 'gene is specific roots in the intact plant and stimulated by lesions in leaf tissue, a combination of characteristics especially desirable for use with an insecticidal or larvicidal gene (see EMBO J 8 (2): 343-350) The TR1 'gene, fused a nptll (neomycin phosphotransferase II) presented similar characteristics. Other promoters with preference for roots include the VfENOD-GRP3 gene promoter (Kuster et al (1995) Plant Mol. Biol. 29 (4): 759-772); and the rolB promoter (Capana ef al. (1994) Plant Mol. Biol. 25 (4): 681-691 See also U.S. Patent Nos .: 5,837,876; 5,750,386; 5,633,363; 5,459,252; 5,401,836; 5.1 10,732; and 5,023,179. "Seed preference" promoters comprise promoters that are active during the development of the seeds, including those that are active in female reproductive tissue around the At the time of anthesis, or during the anthesis, and the promoters of seed storage proteins, promoters that are active during germination of seeds are also of interest, see Thompson et al (1989) BioEssays 10: 108 Said preferential seed promoters include but are not limited to Cim1 (cytokinin-inducing messenger), cZ19B1 (19 kDa corn zein), and miLps (myo-inositol-1-phosphate synthetase). ) (see, WO 00/1 1 177 and U.S. Patent No. 6,225,529, incorporated herein by reference). reference mode). Gamma-zein is a specific promoter of the endosperm. The globulinal (Glb-1) is a representative embryo-specific promoter. For dicotyledons, promoters with preference for seeds include, by way of example, /? - bean phaseollin, napina,? -conglycinin, soybean lectin, cruciferin and the like. For monocotyledons, seed-preferred promoters include, for example, 15 kDa zein from maize, 22 kDa zein, 27 kDa zein, g-zein, waxy, shrunken 1, shrunken 2, globulin 1, etc. See also, WO 00/12733, wherein promoters are disclosed with preference for seeds of the end1 and end2 genes; incorporated here as a reference. Other embryo specific promoters are described in Sato et al. (1996) Proc. Nati Acad. Sci. 93:81 17-8122; Nakase ef al. (1997) Plant J 12: 235-46; and Postma-Haarsma ef al. (1999) Plant Mol. Biol. 39: 257-71. Other promoters with preference for the endosperm are described in Albani ef al. (1984) EMBO 3: 1405-15; Albani ef al. (1999) Theor. Appl. Gen. 98: 1253-62; Albani ef al. (1993) Plant J. 4: 343-55; Mena et al. (1998) The Plant Journal 1 1 6: 53-62, and Wu et al. (1998) Plant Cell Physiology 39: 885-889. As determined above, the promoters of interest include those that are active in the meristem regions, such as developing inflorescence tissues and promoters that direct expression at or around the time of anthesis or during early development of the grain. They may include, for example, the corn Zag2.1 promoter (GenBank X80206; see also U.S. Patent Application Serial No. 10 / 817,483); the corn Zap promoter (also known as ZmMADS; U.S. Patent Application No. 10 / 387,937; WO 03/078590); the corn ckx1 -2 promoter (U.S. Patent Publication No.: 2002-0152500 A1; WO 02/0078438); the corn eepl promoter (U.S. Patent Application No. 10 / 817,483); the corn end2 promoter (U.S. Patent No. 6,528,704 and U.S. Patent Application No. 10 / 310,191); the corn led promoter (U.S. Patent Application No. 09 / 718,754); the corn F3.7 promoter (Baszczynski et al., Maydica 42: 189-201 (1997)); the corn tb1 promoter (Hubbarda et al., Genetics 162: 1927-1935 (2002)); the corn eep2 promoter (U.S. Patent Application No. 10 / 817,483); the thioredoxin H corn promoter (US Provisional Patent Application) No.: 60 / 514,123); the corn promoter Zm40 (U.S. Patent No. 6,403,862 and WO 01/2178); the corn mLIP15 promoter (U.S. Patent No.: 6,479,734); the corn ESR promoter (U.S. Patent Application No.: 0 / 786,679); the corn PCNA2 promoter (U.S. Patent Application No. 10 / 388,359); corn cytokinin oxidase promoters (U.S. Provisional Patent Application No.: 60 / 559,252). Promoters with preference for outbreaks include promoters with preference for meristematic outbreaks, such as the promoters described in Weigal et al. (1992) Ce // 69: 843-859; Access N ° AJ131822; Access N ° Z71981; Access N ° AF049870; the ZAP promoter (U.S. Patent Application Serial No. 10 / 387,937); the corn tbl promoter (Wang ef al. (1999) Nature 398: 236-239) and the promoters with preference for outbreaks described in McAvoy et al. (2003) > Acfa Hort. (ISHS) 625: 379-385. Promoters with preference for meristematic tissues or dividing cells are described in Ito ef al. (1994) Plant Mol. Biol. 24: 863-878; Regad et al. (1995) Mol. Gen. Genet. 248: 703-71 1; Shaul ef al. (1996) Proc. Nati Acad. Sci. EE. UU 93: 4868-4872; Ito et al. (1997) Plant J. 1 1: 983-992; and Trehin ef al. (1997) Plant Mol. Biol. 35: 667-672; Zag1 (Schmidt et al. (1993) The Plant Cell 5: 729-37; and Corn Zag2 (Theissen et al. (1995) Gene 156: 155-166), Genbank Accession No. X80206, all incorporated in this document to Reference mode Promoters with preference for inflorescences include the chalcone synthetase promoter (Van der Meer et al (1990) Plant Mol. Biol. 75: 95-109), LAT52 (Twell et al. (1989) Mol. Gen. Genet 277: 240-245), of pollen-specific genes (Albani ef al (1990) Plant Mol Biol. 15: 605, Zm13 (Wuerrero ef al. (1993) Mol.Ge.Genet. 224: 161- 168), of specific genes of corn pollen (Hamilton et al. (1992) Plant Mol. Biol. 18:21 1 -218), of the gene that is expressed in pollen from sunflower (Baltz et al. (1992) The Plant Journal 2: 713-721), of pollen-specific genes from B. napus (Amoldo et al (1992) J. Cell. Biochem, Abstract No. Y101204).

Stress inducible promoters include salt / water stress inducible promoters, such as P5CS (Zang et al (1997) Plant Sciences 729: 81-89); cold-inducible promoters, such as cor15a (Hajela et al (1990) Plant Physiol. 93: 1246-1252), cor15b (Wilhelm et al. (1993) Plant Mol Biol 23: 1073-1077), wsc120 (Ouellet et al. (1998) FEBS Lett 423-324-328), c7 (Kirch er al. (? 997) Plant Mol Biol. 33: 897-909), c21A (Schneider er al. (1997) Plant Physiol. 13: 335-45); drought-inducible promoters, such as Trg-31 (Chaudhary et al (1996) Plant Mol. Biol. 30: 1247-57), osmosis-inducible promoters, such as Rabbi 7 (Vilardell er al. (1991) Plant Mol. Biol. 77: 985-93) and osmotine (Raghothama er al. (1993) Plant Mol Biol 23: 1 1 17-28); and heat-inducible promoters, such as heat shock proteins (Barros et al. (1992) Plant Mol. 79: 665-75; Marrs et al. (1993) Dev. Genet. 74: 27-41) and smHSP (Waters er al. (1996) J. Experimental Botany 47: 325-338). Other stress-inducible promoters include rip2 (U.S. Patent No. 5,332,808 and U.S. Patent Publication No. 2003/0217393) and rd29a (Yamaguchi-Shinozaki er al. (1993) Mol. Gen. Genetics 236: 331-340). Also of interest are promoters with preference for senescence, such as SEE1 (NCBI AJ494982) and SAG12 (NCBI U37336). Promoters that are not sensitive to stress can also be used in the methods of the invention. The term "non-stress sensitive" means that the level of expression of a sequence operably linked to the promoter is not altered or only minimally altered under stress conditions. Promoters that respond to nitrogen can also be used in the methods of the invention. These promoters include, by way of example, the 22 kDa zein promoter (Spena et al (1982) EMBO J. 1: 1589-1594 and Muller et al. (1995) J. Plant Physiol 745: 606-613); the 19 kDa zein promoter (Pedersen et al. (1982) Cell 29: 1019-1025); the 14 kDa zein promoter (Pedersen et al. (1986) J. Biol. Chem. 267: 6279-6284), the b-32 promoter (Lohmer et al. (1991) EMBO J 70: 617-624); and the nitrite reductase (NiR) promoter (Rastogi et al. (? 997) Plant Mol Biol. 34 (3): 465-76 and Sander et al. (1995) Plant Mol Biol. 27 (1): 165-77 ). For a review of the consensus sequences present in the nitrogen-induced promoters, see for example, Muller et al. (1997) The Plant Journal 72: 281-291). When low levels of expression are desired, weak promoters may be used. Generally, a promoter that drives the expression of a coding sequence at a low level is proposed as a "weak promoter". It is proposed as low level at levels from about 1/1 .000 transcripts to about 1 / 100,000 transcripts, to about 1 / 500,000 transcripts. Alternatively, it is recognized that weak promoters also encompass promoters that are expressed only in a few cells and not in others giving a low total expression level. When a promoter is expressed at unacceptably high levels, portions of the promoter sequence can be deleted, it can be modified to decrease expression levels. Such weak constitutive promoters include, for example, the nuclear promoter of the Rsyn7 promoter (WO 99/43838 and US Patent No.: 6,072,050), the nuclear promoter of 35S CaMV and the like. Other constitutive promoters include, for example, those described in U.S. Pat. N °: 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785; 5,399,680; 5,268,463; and 5,608,142. See also, U.S. Pat. No. 6,177,61 1, incorporated herein by reference.

In general, the expression cassette will comprise a marker gene selected to select the transformed cells. The selected marker genes are used for the selection of transformed cells or tissues. Marker genes include genes that code for antibiotic resistance, such as those coding for neomycin phosphotransferase II (NEO) and hygromycin phosphotransferase (HPT), as well as genes that confer resistance to herbicidal compounds, such as glufosinate ammonium, bromoxynil, imidazolinones and 2,4-dichlorophenoxyacetate (2,4 -D). Other selection markers include phenotypic markers, such as /? -galactosidase and fluorescent proteins such as green fluorescent protein (GFP) (Su et al. (2004) Biotechnol Bioeng 85: 610-9 and Fetter et al. (2004) Plant Cell 16: 215-28), cyano-fluorescent protein (CYP) (Bolte et al (2004) J. Cell Science 117: 943-54 and Kato er al. (2002) Plant Physiol 129: 913-42) and the protein fluorescent yellow (PhiYFP ™ from Evrogen, see, Bolte er al. (2004) J. Cell Science 117: 943-54). For other additional selection markers, see generally, Yarranton (1992) Curr. Opin. Biotech 3: 506-51 1; Christopherson er al. (1992) Proc. Nati Acad. Sci. USA 89: 6314-6318; Yao er al. (1992) Cell 71: 63-72; Reznikoff (1992) Mol. Microbiol. 6: 2419-2422; Barkley et al. (1980) in The Operon, pgs. 177-220; Hu er al. (1987) Cell 48: 555-566; Brown et al. (1987) Cell 49: 603-612; Figge er al. (1988) Cell 52: 713-722; Deuschle er al. (1989) Proc. Nati Acad. Sci. USA 86: 5400-5404; Force to. (1989) Proc. Nati Acad. Sci. USA 86: 2549-2553; Deuschle et al. (1990) Science 248: 480-483; Gossen (1993) PhD Thesis, University of Heidelberg; Reines er al. (1993) Proc. Nati Acad. Sci. USA 90: 1917-1921; Labow er al. (1990) Mol. Cell. Biol. 10: 3343-3356; Zambretti er al. (1992) Proc. Nati Acad. Sci. USA 89: 3952-3956; Baim ef al. (1991) Proc. Nati Acad. Sci. USA 88: 5072-5076; Wyborski er al. (1991) Nucleic Acids Res. 19: 4647-4653; Hillenand-Wissman (1989) Topics Mol. Struc. Biol. 10: 143-162; Degenkolb et al. (1991) Antimicrob. Agents Chemother. 35: 1591-1595; Kleinschnidt et al. (1998) Biochemistry 27: 1094-1 104; Bonin (1993) Doctoral Thesis, University of Heidelberg; Gossen et al. (1992) Proc. Nati Acad. Sci. USA 89: 5547-5551; Oliva eí al. (1992) Antimicrob. Agents Chemother. 36: 913-919; Hlavka I went to. (1985) Handbook of Experimental Pharmacology, Vol. 78 (Springer-Verlag, Berlin); Gilí eí al. (1988) Nature 334: 721-724. These descriptions are incorporated herein by way of reference.

The above list of selected marker genes was not offered in a limiting sense. Any selectable marker gene can be used in the present invention. In one example, the polynucleotide of interest is targeted for its expression in chloroplasts. In this way, when the polynucleotide of interest is not inserted directly into the chloroplast, the expression cassette will further contain a nucleic acid encoding a transit peptide to direct the genetic product of interest to the chloroplasts. Such transit peptides are known in the art. See, for example, Von Heijne et al. (1991) Plant Mol. Biol. Rep. 9: 104-126; Clark went to. (1989) J. Biol. Chem. 264: 17544-17550; Della-Cioppa e al al. (1987) Plant Physiol. 84: 965-968; Romer eí al. (1993) Biochem. Biophys. Res. Commun. 196: 1414-1421; and Shah I went to. (1986) Science 233: 478-481. Chloroplast targeting sequences are known in the art and include the small subunit of ribulose-1, 5-bisphosphate carboxylase (Rubisco) of chloroplasts (by Castro Silva Filho et al. (1996) Plant Mol. Biol. 30: 769 -780; Schnell et al. (1991) J. Biol. Chem. 266 (5): 3335-3342); 5- (enolpiruvil) shikimate-3-phosphate synthetase (EPSPS) (Archer et al (1990) J. Bioenerg, Biomemb.22 (6): 789-810); tryptophan synthetase (Zhao et al. (1995) J.

Biol. Chem. 270 (11): 6081-6087); plastocyanin (Lawrence et al (1997) J. Biol. Chem. 272 (33): 20357-20363); corismate synthetase (Schmidt et al (1993) J. Biol. Chem. 268 (36): 27447-27457); and the light sequestering chlorophyll a / b binding protein (LHBP) (Lamppa et al (1988) J. Biol. Chem. 263: 14996-14999). See also Von Heijne ef al. (1991) Plant Mol. Biol. Rep. 9: 104-126; Clark et al. (1989) J. Biol. Chem. 264: 17544-17550; Della-Cioppa et al. (1987) Plant Physiol. 84: 965-968; Romer et al. (1993) Biochem. Biophys. Res. Commun. 196: 1414-1421; and Shah et al. (1986) Science 233: 478-481. Methods for transforming chloroplasts are known in the art. See, for example, Svab et al. (1990) Proc. Nati Acad. Sci. EE. UU 87: 8526-8530; Svab and Maliga (1993) Proc. Nati Acad. Sci. EE. UU 90: 913-917; Svab and Maliga (1993) EMBO J. 12: 601-606. The method is based on the gun distribution of DNA particles containing a selectable marker and the targeting of the DNA to the plastid genome through homologous recombination. In addition, plastid transformation can be effected by transactivation of a silent transgene contained in the plastids by expression with preference for tissues of an RNA polymerase encoded in the nucleus and directed to plastids. Said system is described in McBride et al. (1994) Proc. Nati Acad. Sci. EE. UU 91: 7301 -7305. The polynucleotides of interest that will be directed to the chloroplasts can be optimized for their expression in the chloroplast in order to compensate for the differences in codon usage between the plant nucleus and this organelle. In this way, the polynucleotide of interest can be synthesized using codons, preferably chloroplasts. See, for example, U.S. Pat. No. 5,380,831, incorporated herein by reference.

The methods of the invention comprise the introduction of a polypeptide or polynucleotide into a plant. The term "introduce" means to present to the plant the polynucleotide or polypeptide in such a way that the sequence achieves access to the interior of the cell of a plant. The methods of the invention do not depend on a particular method for introducing the sequence into a plant, only that the polynucleotide or polypeptide can access the interior of at least one cell of the plant. Methods for introducing polynucleotides or polypeptides into plants are known in the art and include, by way of example, stable transformation methods, transient transformation methods and virus mediated methods. A "stable transformation" means that the nucleotide construct introduced into the plant is integrated into the genome of the plant and that it can be inherited by the plant's progeny. A "transient transformation" means that the polynucleotide is introduced into the plant and that it is not integrated into the genome of the plant or that a polypeptide is introduced into the plant. Transformation protocols, as well as protocols for introducing polypeptide or polynucleotide sequences in plants, can vary according to the type of plant or plant cell, ie monocot or dicot, intended for transformation. Methods for introducing polypeptides or polynucleotides into suitable plant cells include microinjection Crossway et al. (1986) Biotechniques 4: 320-334; electroporation, Riggs et al. (1986) Proc. Nati Acad. Sci. USA 83: 5602-5606; Agrobacterium-mediated transformation (Townsend et al, U.S. Patent No. 5,563,055; Zhao et al., U.S. Patent No.: 5,981, 840); direct gene transfer (Paszkowski et al., (1984) EMBO J. 3: 2717-2722) and particle ballistic acceleration (see, for example, Sanford et al., U.S. Patent No. 4,945,050; Tomes et al., U.S. Patent No.: . 879,918; Tomes et al., U.S. Pat. N °: 5,886,244; Bidney et al., U.S. Pat. No. 5,932,782; Tomes et al. (1995) "Direct DNA Transfer into Intact Plant Cells via Microprojectile Bombardment", in Plant Cell, Tissue, and Organ Culture: Fundamental Methods, ed. Gamborg and Phillips (Springer-Verlag, Berlin); and McCabe et al. (1988) Biotechnology 6: 923-926; and transformation of Lec1 (WO 00/28058). See also Weissinger et al. (1988) Ann Rev. Genet. 22: 421-477; Sanford et al. (1987) Particulate Science and Technology 5: 27-37 (onion); Christou et al. (1988) Plant Physiol. 87: 671 -674 (soybean); McCabe ef al. (1988) Bio / Technology 6: 923-926 (soybean); Finer and McMullen (1991) In vitro Cell Dev. Biol. 27P: 175-182 (soybean); Singh et al. (1998) Theor. Appl. Genet 96: 319-324 (soybean); Datta et al. (1990) Biotechnology 8: 736-740 (rice); Klein et al. (1988) Proc. Nati Acad. Sci. USA 85: 4305-4309 (corn); Klein et al. (1988) Biotechnology 6: 559-563 (corn); Tomes, U.S. Pat. N °: 5,240,855; Buising ef al., U.S. Pat. Nos .: 5,322,783 and 5,324,646; Tomes ef al. (1995) "Direct DNA Transfer into Intact Plant Cells via Microprojectile Bombardment", in Plant Cell, Tissue, and Organ Culture: Fundamental Methods, ed. Gamborg (Springer-Verlag, Berlin) (corn); Klein ef al. (1988) Plant Physiol. 91: 440-444 (corn); Fromm ef al. (1990) Biotechnology 8: 833-839 (corn); Hooykaas-Van Slogteren ef al. (1984) Nature (London) 31 1: 763-764; Bowen et ai, U.S. Pat. N °: 5,736,369 (cereals); Bytebier et al. (1987) Proc. Nati Acad. Sci. USA 84: 5345-5349 (Liliaceae); De Wet ef al. (1985) in The Experimental Manipulation of Ovule Tissues, ed. Chapman ef al. (Longman, New York), pgs. 197-209 (pollen); Kaeppler et al. (1990) Plant Cell Reports 9: 415-418; and Kaeppler ef al. (1992) Theor. Appl. Genet 84: 560-566 (fiber mediated transformation); D. Halluin ef al. (1992) Plant Cell 4: 1495-1505 (electroporation); Li ef al. (1993; Plant Cell Reports 12: 250-255 and Christou and Ford (1995) Annals of Botany 75: 407-413 (rice); Osjoda ef al. (1996) Nature Biotechnology 14: 745-750 (corn by Agrobacterium tumefaciens); whose contents are incorporated in this document as a reference. In specific embodiments, the histidine kinase sequences of the invention can be provided in a plant using a variety of transient transformation methods. Such transient transformation methods include, by way of example, the introduction of the histidine kinase protein, or variants or fragments thereof, directly into the plant or the introduction of a histidine kinase transcript into the plant. Such methods include, for example, microinjection or particle bombardment. See, for example, Crossway e al. (1986) Mol Gen. Genet. 202: 179-185; Nomura eí al. (1986) Plant Sci. 44: 53-58; Hepler er al. (? 994) Proc. Nati Acad. Sci. EE. UU 91: 2176-2180 and Hush e al. (1994) The Journal of Cell Science 707: 775-784, the contents of which are incorporated herein by reference. Alternatively, the histidine kinase polynucleotide can be transiently transformed in the plant using techniques known in the art. Such techniques include a system of viral vectors and the precipitation of the polynucleotide in a manner that prevents subsequent release of the DNA. Accordingly, the transcription of the DNA bound to the particles can take place, but the frequency that is released to integrate into the genome is very small. Such methods include the use of coated particles with polyethylimine (PEI, Sigma No. P3143). In other examples, the polynucleotide of the invention can be introduced into plants by contacting said plants with a virus or with viral nucleic acids. In general, said methods comprise the incorporation of a nucleotide construct of the invention into a viral DNA or RNA molecule. It is considered that the histidine kinase of the invention can be synthesized initially as part of a viral polyprotein, which can then be processed by proteolysis in vivo or in vitro to produce the desired recombinant protein. In addition, it is considered that the promoters of the invention also encompass the promoters used for transcription by viral RNA polymerases. Methods for introducing polynucleotides into plants and expressing a protein encoded therein, comprising viral DNA or RNA molecules, are known in the art. See, for example, U.S. Pat. Nos .: 5,889,191, 5,889,190, 5,866,785, 5,589,367, 5,316,931 and Porta et al. (1996) Molecular Biotechnology 5: 209-221; incorporated in this document as a reference. Methods for a targeted insertion of a polynucleotide at a specific location in the genome of the plant are known in the art. In one example, the insertion of the polynucleotide into a desired genomic location is achieved using a site-specific recombination system. See, for example, W099 / 25821, W099 / 25854, WO99 / 25840, W099 / 25855 and W099 / 25853; whose contents are incorporated in this document as a reference. Briefly, the polynucleotide of the invention can be contained in a transfer cassette flanked by two non-identical recombination sites. The transfer cassette is introduced into a plant that has stably incorporated into its genome its target site that is flanked by two non-identical recombination sites that correspond to the sites of the transfer cassette. An appropriate recombinase is provided and the transfer cassette is integrated into the target site. The polynucleotide of interest is thus integrated into a specific chromosomal position in the genome of the plant. The cells, which were transformed, can be grown to obtain plants according to conventional manners. See, for example, McCormick et al. (1986) Plant Cell Reports, 5:81 -84. Then you can grow these plants and you they can pollinate with the same transformed strain or with different strains and then the resulting progeny can be identified which appropriately expresses the desired phenotypic characteristic. Two or more generations can be grown to ensure that the expression of the desired phenotypic characteristics is maintained and stably inherited and then the seeds are harvested to ensure that the expression of the desired phenotypic characteristics is carried out. In this manner, the present invention provides transformed seeds (also referred to as "transgenic seeds") that contain a polynucleotide of the invention, for example, an expression cassette of the invention, stably incorporated into its genome. Pedigree breeding begins with the crossing of two genotypes, such as an elite line of interest and some other line that possesses one or more desirable characteristics (i.e., that they have stably incorporated a polynucleotide of the invention, presenting a activity and / or modulated level of the polypeptide of the invention, etc.) that complements the elite line of interest. If the two original parents do not provide all the desired characteristics, other sources can be included in the breeding population. In the pedigree method, higher plants are autocrossed and selected in successive branch generations. In subsequent filial generations the heterozygous condition gives rise to homogeneous lines as a result of self-pollination and selection. Typically, in the pedigree breeding method, self-crossing and selection is practiced in five or more successive filial generations: F1? F2; F2? F3; F3? F4; F4? F5, etc. After sufficient endogamy, the successive filial generations will serve to increase the seeds of the developed endogamous. Preferably, the inbred line comprises homozygous alleles in about 95% or more of their loci.

In addition to its use to create a backcross conversion, the backcross can also be used in combination with pedigree breeding to modify an elite line of interest and a hybrid obtained using the modified elite line. As described above, backcrossing can be used to transfer one or more specifically desirable characteristics of a line, the donor parent, to an inbred named recurrent parent, which has good general agronomic characteristics although it does not possess the desirable characteristics. However, the same procedure can be used to move the progeny towards the genotype of the recurrent parent and at the same time retain many components of the non-recurrent parent, stopping the backcross at an early stage and proceeding with self-crossing and selection. For example, an F1 is created, such as a commercial hybrid. This commercial hybrid can be backcrossed with one of its progenitor lines to create a BC1 or BC2. The progeny are autocrossed and selected in such a way that the newly developed endogamous possesses many of the attributes of the recurrent parent and also several of the desired attributes of the non-recurrent parent. This approach allows relieving the value and strength of the recurrent parent for use in new hybrids and breeding. Therefore, an example of this invention is a method for making by inverse conversion an inbred corn line of interest, comprising the steps of crossing a plant of the corn inbred line of interest with a donor plant comprising a gene or transgene that confers a desired characteristic (e.g., enhanced expression of a histidine kinase of the invention), selects a plant from the F1 progeny comprising said mutant gene or transgene that confers the desired characteristic and backcrosses the selected F1 progeny plant with a plant of the line Inbreeding corn of interest. This method may further comprise the step of obtaining a molecular marker profile of the inbred corn line of interest and using said molecular marker profile to select a progeny plant with the desired characteristic and the molecular marker profile of the inbred line of interest. In the same way, this method can be used to produce F1 hybrid seeds by adding a final crossing step of the maize inbred line of interest converted to the desired characteristic with a different maize plant to obtain an F1 hybrid maize seed. which comprises a mutant gene or transgene that confers the desired characteristic. Recurrent selection is a method used in a plant breeding program to improve a population of plants. The method comprises cross-pollination between individual plants to form the progeny. Progeny are cultured and superior progeny are selected using numerous selection methods, including individual plants, progeny of half-sisters, progeny of full sisters, self-crossbred progeny and superior crossover. The selected progeny are cross-pollinated to form the progeny of another population. This population is sown and again higher plants are selected to re-cross-pollinate them. Recurring selection is a cyclic process and therefore can be repeated as many times as desired. The objective of the recurrent selection is to improve the characteristics of a population. The improved population can then be used as a source of breeding material to obtain inbred lines to be used as hybrids or as progenitors for a synthetic cultivar. A synthetic cultivar is the resulting progeny formed by the cross-linking of several selected inbreds.

Mass selection is a useful technique especially when used in conjunction with improved selection by molecular markers. In mass selection, individual seeds are selected on the basis of phenotype and / or genotype. These selected seeds are then grouped and used to obtain the next generation. Mass selection requires the cultivation of a population of plants in a growing plot, the self-pollination of the plants, the harvesting of the seeds en masse and the subsequent use of a sample of the seeds harvested en masse to plant the next generation. Instead of self-pollination, targeted pollination could be used as part of the breeding program. As used herein, the term "plant" includes plant cells, plant protoplasts, tissue cultures of plant cells from which it is possible to regenerate a plant, plant callus, plant masses and plant cells that are intact in plants or in plants. parts of plants such as embryos, pollen, ovules, seeds, leaves, flowers, branches, fruits, grains, spikes, marlos, chalas, stems, roots, tips of roots, anthers and similar. The term "grain" refers to mature seed produced by commercial breeders for purposes other than cultivating or reproducing the species. Progeny, variants and mutants of the regenerated plants are also included within the scope of the invention, provided that these parts comprise the introduced polynucleotides. The present invention can be used for the transformation of any plant species, including monocotyledons and dicots. Examples of plant species of interest include, by way of example, corn (Zea mays), Brassica sp. (for example, B. napus, B. rapa, B. júncea), particularly those Brassica species that are useful as sources of seed oil, alfalfa (Medicago sativa), rice (Oryza sativa), rye (Sécale cereale), sorghum (Sorghum bicolor, Sorghum vulgare), millet (for example, pearl millet (Pennisetum glaucum), millet proso (Panicum miliaceum), millet fox tail (Setaria italica), finger millet (Eleusine coracana), sunflower (Helianthus annuus), safflower (Carthamus tinctorius), wheat (Triticum aestivum), soybean (Glycine max), tobacco (Nicotiana tabacum), potato (Solanum tuberosum), peanut (Arachis hypogaea), cotton (Gossypium barbadense, Gossypium hirsutum), sweet potato (Ipomoea batatus), cassava (Manihot esculenta), coffee (Cofea spp.), Coconut (Cocos nucífera) , pineapple (Ananas comosus), citrus trees (Citrus spp.), cacao (Theobroma cacao), tea (Camellia sinensis), banana (Musa spp), avocado (Percea americana), fig (Ficus casica), guayava (Psidium guajava) , mango (Mangifera indica), olive (Olea europaea), papaya (Carica papaya), cashew (Anacardium occidentale), macadamia (Macadamia integrifolia), almond (Prunus amygdalus), beet (Beta vulgaris), sugar cane (Saccharum spp. ), oats, barley, vegetables, ornamentals, grasses and conifers. Vegetables include tomatoes (Lycopersicon esculentum), lettuce (for example, Lactuca sativa), green beans (Phaseolus vulgaris), crescent beans (Phaseolus limensis), peas (Lathyrus spp.) And members of the genus Curcumis such as cucumber (C sativus), cantaloupe melon (C. cantalupensis) and yellow melon (C. meló). Ornamental plants include azaleas (Rhododendron spp.), Hydrangea (Macrophylla hydrangea), hibiscus (Hibiscus rosasanensis), roses (Rosa spp.), Tulips (Tulipa spp.), Daffodils (Narcissus spp.), Petunias (Petunia ida), carnations (Dianthus caryophyllus), shepherdess (Euphorbia pulcherrima) and chrysanthemums. Conifers that can be employed in the practice of the present invention include, for example, pines such as loblolly pine (Pinus taeda), incense pine (Pinus elliotii), ponderosa pine (Pinus ponderosa), lodgepole pine (Pinus contorta) ), and Monterey pine (Pinus radiata); Douglas fir (Pseudotsuga menziesii); Western Tsuga (Tsuga canadensis); Sitka fir (Picea glauca); dryness { Sequoia sempervirens); true fir trees, such as, golden fir. { Abies amabilis); and fir balsam (Abies balsamea); and cedars, such as the red cedar of the West (Thuja plicata) and the yellow cedar of Alaska (Chamaecyparis nootkatensis). In specific examples, the plants of the present invention are crop plants (e.g., corn, alfalfa, sunflower, Brassica, soybean, cotton, safflower, peanut, sorghum, wheat, millet, tobacco, etc.). In other examples, corn and soybean plants are preferred and in other embodiments the preferred plants are corn. Other plants of interest include grain plants that provide seeds of interest, oilseed plants and leguminous plants. The seeds of interest include grain seeds, such as corn, wheat, barley, rice, sorghum, rye, etc. Oilseed plants include cotton, soybean, safflower, sunflower, Brassica, corn, alfalfa, palm, coconut, etc. Legume plants include beans and peas. The beans include guar, carob bean, fenugreek, soybeans, garden beans, cowpeas, beans, beans, common bean, lentils, chickpeas, etc. The histidine kinases of the invention can be produced in any host cell of interest. The polynucleotides of the invention can be used to express the histidine kinases of the invention in non-human host cells, including, by way of example, plant cells, algal cells, bacterial cells, animal cells and fungal cells. Said fungal cells include, for example, yeast cells. For expression in a host cell of interest, the polynucleotide of the invention is operably linked to a promoter that directs expression in the host cell. The invention does not depend on a particular promoter or method for transforming a host cell with the construction of polynucleotides. You can use any promoter and / or any method for transforming the host cell of interest into the methods of the present invention. Accordingly, the present invention further provides non-human host cells transformed with at least one polynucleotide of the invention and methods for obtaining said transformed host cells. A method is provided for modulating the concentration and / or activity of the polypeptide of the present invention in a plant. In general, the concentration and / or activity is increased or decreased by at least 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% with relation to the plant, plant part or native control cell that does not contain the sequence of the invention introduced. The modulation in the present invention can take place during and / or after the growth of the plant up to the desired stage of development. In specific examples, the polypeptides of the present invention are modulated in monocotyledons, in particular in corn. The level of expression of the histidine kinase polypeptide can be measured directly, for example, by evaluating the level of the histidine kinase polypeptide in the plant, or indirectly, for example, by measuring the histidine kinase activity in the plant or by monitoring the plant phenotype. . Methods for determining histidine kinase activity are described elsewhere herein. In specific examples, the polypeptide or the polynucleotide of the invention is introduced into the plant cell. Subsequently, a plant cell containing the introduced sequence of the invention is selected using methods known to those skilled in the art such as, by way of example, Southern blot analysis, DNA sequencing, PCR analysis or phenotypic analysis. The plant or plant part altered or modified according to the preceding embodiments is cultivated under plant-forming conditions for a time sufficient to modulate the concentration and / or activity of the polypeptide of histidine kinase in the plant. Plant forming conditions are well known in the art and are briefly described elsewhere herein. It is also considered that the level and / or activity of the polypeptide can be modulated using a polynucleotide that is not capable of directing, in a transformed plant, the expression of a protein or an RNA. For example, the polynucleotides of the invention can be used to design polynucleotide constructs that can be employed in methods for altering or mutating a genomic nucleotide sequence in an organism. Such polynucleotide constructions include, by way of example, RNA: DNA vectors, RNA vectors: mutation DNA, RNA: DNA repair vectors, mixed double oligonucleotides, self-complementary RNA: DNA oligonucleotides and recombinogenic oligonucleobases. Said nucleotide constructs and methods of using them are known in the art. See, U.S. Pat. No. 5,565,350; 5,731,181; 5,756,325; 5,760,012; 5,795,972; and 5,871,984; whose contents are incorporated in this document as a reference. See also, WO 98/49350, WO 99/07865, WO 99/25821 and Beetham et al. (1999) Proc. Nati Acad. Sci. EE. UU 96: 8774-8778; incorporated in this document as a reference. It is therefore considered that the methods of the present invention do not depend on the incorporation of the entire polynucleotide into the genome, only that the plant or a cell thereof is altered as a result of the introduction of the polynucleotide into a cell. In one example of the invention, it is possible to alter the genome after the introduction of the polynucleotide into a cell. For example, the polynucleotide, or any part thereof, can be incorporated into the genome of the plant. Alterations to the genome of the present invention include, by way of example, additions, deletions and substitutions of nucleotides in the genome While the methods of the present invention do not depend on additions, deletions and substitutions of any particular number of nucleotides, it is considered that said additions, deletions or substitutions comprise at least one nucleotide. In one example, the activity and / or the level of the histidine kinase polypeptide of the invention increases. Said increase in the level and / or activity of a histidine kinase polypeptide of the invention can be achieved by providing the plant with a histidine kinase polypeptide. As described elsewhere herein, there are many methods that are known in the art to provide a polypeptide to a plant including, by way of example, the direct introduction of the polypeptide into the plant, and the introduction into the plant (from transient or stable form) a construction of a polynucleotide that encodes a polypeptide having histidine kinase activity. It is also considered that the methods of the invention can employ a polynucleotide which is not capable of directing, in the transformed plant, the expression of a protein or an RNA. Accordingly, the level and / or activity of a histidine kinase polypeptide can be increased by altering the gene encoding the histidine kinase polypeptide or by altering or affecting its promoter. See, for example, Kmiec, U.S. Pat. No. 5,565,350; Zarling ei al., PCT / US93 / 03868. Thus, mutagenized plants containing mutations in the histidine kinase genes are provided, where said mutations increase the expression of the histidine kinase gene or increase the histidine kinase activity of the encoded histidine kinase polypeptide. In other examples, the activity and / or level of the histidine kinase polypeptide of the invention is reduced or eliminated by introducing into the plant a polynucleotide that inhibits the level or activity of the histidine kinase polypeptide. of the invention. The polynucleotide can inhibit the expression of histidine kinase directly, by preventing translation of the histidine kinase messenger RNA, or indirectly, by inhibiting the transcription or translation of a histidine kinase gene encoding a histidine kinase protein. Methods for inhibiting or eliminating the expression of a gene in a plant are well known in the art and any of said methods in the present invention can be used to inhibit the expression of a histidine kinase polypeptide. In other examples of the invention, the activity of a histidine kinase polypeptide is reduced or eliminated by transforming the plant cell with a sequence encoding a polypeptide that inhibits the activity of the histidine kinase polypeptide. In other embodiments, the activity of a histidine kinase polypeptide can be reduced or eliminated by breaking the gene encoding the histidine kinase polypeptide. The invention encompasses mutagenized plants that contain mutations in the histidine kinase genes, wherein said mutations reduce the expression of the histidine kinase gene or inhibit the histidine kinase activity of the encoded histidine kinase polypeptide. The reduction of the activity of specific genes (also known as gene silencing or gene suppression) is desirable for various aspects of genetic engineering in plants. There are many gene-scenting techniques that are well known to those skilled in the art, including, by way of example, antisense technology (see, e.g., Sheehy et al. (1988) Proc. Nati. Acad. Sci. U.S.A. 85: 8805-8809; and U.S. Patent Nos .: 5,107,065; 5,453,566; and 5,759,829); cosuppression (for example, Taylor (1997) Plant Cell 9: 1245; Jorgensen (1990) Trends Biotech 8 (12): 340-344; Flavell (1994) Proc. Nati. Acad. Sci. USA 91: 3490 -3496; Finnegan et al. (1994) Bio / Technology 12: 883-888; and Neuhuber et al. (1994) Mol.

Gen. Genet. 244: 230-241); RNA interference (Napoli et al. (1990) Plant Cell 2: 279-289; U.S. Patent No. 5,034,323; Sharp (1999) Genes Dev. 13: 139-141; Zamore I went to. (2000) Cell 101: 25-33; and Montgomery et al. (1998) Proc. Nati Acad. Sci. USA 95: 15502-15507), gene silencing induced by viruses (Burton er al. (2000) Plant Cell 12: 691-705; and Baulcombe (1999) Curr. Op. Plant Bio. 2: 109-1 13); specific ribozymes of the target RNA (Haseloff et al. (1988) Nature 334: 585-591); fork structures (Mette et al. (2002) EMBO J. 19: 5194-5201; Smith er al. (2000) Nature 407: 319-320; WO 99/53050; WO 02/00904; WO 98/53083; Chuang and Meyerowitz (2000) Proc. Nati, Acad. Sci. USA 97: 4985-4990; Stoutjesdijk et al. (2002) Plant Physiol. 129: 1723-1731; Waterhouse and Helliwell (2003) Nat. Rev. Genet 4: 29-38; Pandolfini et al., BMC Biotechnology 3: 7, U.S. Patent Publication No.: 20030175965; Panstruga et al. (2003) Mol. Biol. Rep. 30: 135-140; Wesley et al. (2001) Plant J. 27: 581-590; Wang and Waterhouse (2001) Curr. Opin. Plant Biol. 5: 146-150; U.S. Patent Publication No.: 20030180945; and WO 02 / 00904, all incorporated in this document as a reference); ribozymes (Steinecke et al. (1 992) EMBO J. 1 1: 1 525; and Perriman et al. (1993) Antisense Res. Dev. 3: 253); directed modification mediated by oligonucleotides (e.g., WO 03/076574 and WO 99/25853); molecules sought by Zn fingers (for example, WO 01/52620, WO 03/048345, and WO 00/42219); labeling with transposons (Maes et al. (1999) Trends Plant Sci. 4: 90-96; Dharmapuri and Sonti (1999) FEMS Microbiol.Lett.179: 53-59; Meissner et al. (2000) Plant J. 22: 265-274; Phogat et al. (2000) J. Biosci. 25: 57-63; Walbot (2000) Curr. Opin. Plant Biol. 2: 103-107; Gai et al. (2000) Nucleic Acids Res. 28 : 94-96; Fitzmaurice et al. (1999) Genetics 153: 1919-1928; Bensen et al. (1995) Plant Cell 7: 75-84; Mena et al. (1996) Science 274: 1537-1 540; U.S. Patent No. 5,962,764); whose contents are incorporated in this document as a reference; and other methods or combinations of the mentioned methods known to those skilled in the art. The polynucleotides of the present invention can be used oriented in the sense of the reading frame to suppress the expression of endogenous genes in plants. Methods for suppressing gene expression in plants with oriented polynucleotides in the sense of the reading frame are known in the art. The methods generally comprise transforming plants with a DNA construct comprising a promoter that directs expression in a plant operably linked to at least a portion of a polynucleotide corresponding to the transcript of the endogenous gene. Typically, such a nucleotide sequence has a substantial sequence identity with the transcript sequence of the endogenous gene, preferably more than about 65% sequence identity, more preferably more than about 85% sequence identity, more preferably more than about 95% sequence identity. Overexpression of the RNA molecule can result in reduced expression of the native gene. Accordingly, multiple lines of plants transformed with the cosuppression expression cassette are examined to identify those that show the greatest inhibition of histidine kinase polypeptide expression. See, U.S. Pat. Nos .: 5,283,184 and 5,034,323; incorporated in this document as a reference. Accordingly, many methods can be used to reduce or eliminate the activity of a histidine kinase polypeptide. In addition, more than one method can be used to reduce the activity of a single histidine kinase polypeptide. In addition, combinations of methods can be employed to reduce or eliminate the activity of the histidine kinase polypeptides.

In some examples of the present invention, a maize cell is transformed with an expression cassette capable of expressing a polynucleotide that inhibits the expression of histidine kinase. The term "expression" as used herein refers to the biosynthesis of a gene product, including the transcription and / or translation of said genetic product. For example, for the purposes of the present invention, an expression cassette capable of expressing a polynucleotide that inhibits the expression of at least one corn histidine kinase polypeptide is an expression cassette capable of producing an RNA molecule that inhibits transcription and / or translation of at least one corn histidine kinase polypeptide of the invention. The "expression" or "production" of a protein or polypeptide from a DNA molecule refers to the transcription and translation of the coding sequence to produce the protein or polypeptide, while the "expression" or "production" of a protein or polypeptide from an RNA molecule refers to the translation of the RNA coding sequence to produce the protein or polypeptide. The polynucleotide used for cosuppression may correspond to all or a portion of the sequence encoding histidine kinase, all or part of the 5 'and / or 3' untranslated region of a histidine kinase transcript, or all or part of the coding sequence and the untranslated regions of a transcript encoding a histidine kinase. In some embodiments where the polynucleotide comprises all or part of the coding region of the histidine kinase polypeptide, the expression cassette is designed to eliminate the start codon of the polynucleotide so that no protein product will be translated. Cosuppression can be used to inhibit the expression of plant genes to produce plants that have levels of non-detectable for the proteins encoded by these genes. See, for example, Broin et al. (2002) Plant Cell 14: 1417-1432. Cosuppression can also be used to inhibit the expression of multiple proteins in the same plant. See, for example, U.S. Pat. No.: Methods for using cosuppression to inhibit the expression of endogenous genes in plants are described in Flavell et al. (1994) Proc. Nati Acad. Sci. EE. UU 91: 3490-3496; Jorgensen e to al. (1996) Plant Mol. Biol. 31: 957-973; Johansen and Carrington (2001) Plant Physiol. 126: 930-938; Broin et al. (2002) Plant Cell 4: 14 7- 432; Stoutjesdijk eí al (2002) Plant Physiol. 129: 723-731; Yu ef al. (2003) Phytochemistry 63: 753-763; and U.S. Pat. Nos .: 5,034,323, 5,283,184 and 5,942,657; whose contents are incorporated in this document as a reference. The effectiveness of the cosuppression can be increased by including a poly-dT region in the expression cassette at a 3 'position with respect to the sequence oriented in the direction of the reading frame and 5' with respect to the polyadenylation signal. See, U.S. Patent Publication. No.: 20020048814, incorporated herein by reference. Typically, such a nucleotide sequence has a substantial sequence identity with the transcript sequence of the endogenous gene, preferably more than about 65% sequence identity, more preferably more than about 85% sequence identity, more preferably more than about 95% sequence identity. See, U.S. Pat. Nos .: 5,283,184 and 5,034,323; incorporated in this document as a reference. In some examples of the invention, inhibition of histidine kinase expression can be achieved by antisense suppression. For antisense suppression, the expression cassette is designed to express an RNA molecule complementary to all or part of the messenger RNA encoding histidine kinase. Overexpression of the antisense RNA molecule may result in reduced expression of the native gene. Accordingly, multiple lines of plants transformed with the expression cassette for antisense suppression are examined in order to identify those that show the highest inhibition of histidine kinase expression. The polynucleotide of use in antisense suppression is designed to hybridize to the corresponding mRNA and may comprise all or part of the complement of the sequence encoding the histidine kinase, all or part of the complement of the 5 'and / or untranslated region. 'of the histidine kinase transcript or all or part of the complement of the coding sequence and the untranslated regions of a transcript encoding the histidine kinase. In addition, the antisense polynucleotide can be completely complementary (ie, 100% identical to the complement of the sequence of interest) or partially complementary (ie, less than 100% identical to the complement of the sequence of interest) of the sequence of interest . Antisense suppression can be used to inhibit the expression of multiple proteins in the same plant. See, for example, U.S. Pat. N °: 5,942,657. Still further, portions of the antisense nucleotides can be used to interrupt the expression of the gene of interest. In general, sequences of at least 50 nucleotides, 100 nucleotides, 200 nucleotides, 300, 400, 450, 500, 550 or more nucleotides can be used. Methods for using antisense suppression in inhibiting the expression of endogenous genes in plants are described, for example, in Liu ef al. (2002) Plant Physiol. 129: 1732-1743 and in U.S. Pat. No. 5,759,829 and 5,942,657, the contents of which are incorporated herein by reference. It is possible to increase the efficacy of antisense suppression by including a poly-dT region in the expression cassette at a 3 'position with respect to the antisense sequence and 5 * with respect to the polyadenylation signal. See, Publication U.S. Pat. No.: 20020048814, incorporated herein by reference. In some examples of the invention, inhibition of the expression of a histidine kinase can be achieved by interference with double-stranded RNA (dsRNA). For the cDNA interference, an RNA molecule oriented in the sense of the reading frame is expressed as that described above for cosuppression and an antisense RNA molecule that is completely or partially complementary to the RNA molecule oriented in the sense of the reading frame in the same cell, resulting in the inhibition of the expression of the corresponding endogenous messenger RNA. The expression of the molecules oriented in the sense of the reading and antisense framework can be achieved by designing the expression cassette to contain a sequence oriented sequence oriented in the sense of the reading frame and an antisense sequence. Alternatively, separate expression cassettes can be used for the sequences oriented in the sense of the reading frame and the antisense sequences. Multiple lines of transformed plants can be examined with the expression cassette (s) for interference with dsRNA in order to identify the plant lines that show the greatest inhibition of histidine kinase expression. Methods for using cDNA interference in the inhibition of the expression of endogenous plant genes are described in Waterhouse et al. (1998) Proc. Nati Acad. Sci. USA 95: 13959-13964, Liu et al. (2002) Plant Physiol. 129: 1732-1743 and WO 99/49029, WO 99/53050, WO 99/61631 and WO 00/49035; whose contents are incorporated in this document as a reference. In some examples of the invention, the inhibition of the expression of one or more histidine quinases can be obtained by interfering with RNA in hairpin (shRNA) or interference with hairpin RNA containing introns (shRNA). These methods are highly effective in inhibiting the expression of endogenous genes. See, Waterhouse and Helliwell (2003) Nat. Rev. Genet. 4: 29-38 and the references cited therein. For interference with hRNA, an expression cassette is designed to express an RNA molecule that hybridizes to itself to form a hairpin structure comprising a single chain loop region and a base pairing stem. The stalk region with base pairing comprises a sequence oriented in the sense of the reading frame corresponding to all or part of the endogenous messenger RNA encoding the gene whose expression it is desired to inhibit and an antisense sequence that is completely or partially complementary to the sequence oriented in the sense of the reading frame. Alternatively, the stem-pairing stem region may comprise complementary sequences corresponding to a selected promoter region, resulting in silencing of the coding sequence operably linked to said selected promoter. See, for example, Mette et al. (2000) EMBO J 19 (19): 5194-5201. Accordingly, the paired base region of the molecule generally determines the specificity of the interfering RNA. RNAh molecules are highly effective in inhibiting the expression of endogenous genes and the interfering RNA they induce is inherited by subsequent generations of plants. See, for example, Chuang and Meyerowitz (2000) Proc. Nati Acad. Sci. EE. UU 97: 4985-4990; Stoutjesdijk I went to. (2002) Plant Physiol. and Waterhouse and Helliwell (2003) Nat. Rev. Genet. 4: 29-38. Methods for using interference with hRNA to inhibit or silence gene expression are described, for example, in Chuang and Meyerowitz (2000) Proc. Nati Acad. Sci. EE. UU 97: 4985-4990; Stoutjesdijk ef al. (2002) Plant Physiol. 129: 1723-1731; Waterhouse and Helliwell (2003) Nal Rev. Genet. 4: 29-38; Pandolfini ef al. BMC Biotechnology 3: 7 and U.S. Patent Publication. N °: 20030175965; whose contents are incorporated in this document as a reference. Panstruga ef al. described a transient assay to determine the efficacy of hsRNA constructs to silence gene expression in vivo. (2003) Mol. Biol. Rep. 30: 135-140, incorporated herein by reference). For the RNAi, the interfering molecules have the same general structure as for the hRNA, but the RNA molecule also comprises an intron capable of being processed in the cell in which the RNAi is expressed. The use of an intron minimizes the size of the loop in the hairpin RNA molecule after processing, and this increases the effectiveness of the interference. See, for example, Smith et al. (2000) Nature 407: 319-320. In fact, Smith et al. show 100% suppression of endogenous gene expression using RNAi-mediated interference. Methods for using interference with RNAi to inhibit the expression of endogenous plant genes are described, for example, in Smith et al. (2000) Nature 407: 319-320; Wesley ef al. (2001) Plant J. 27: 581-590; Wang and Waterhouse (2001) Curr. Opin. Plant Biol. 5: 146-150; Waterhouse and Helliwell (2003) Nat. Rev. Genet. 4: 29-38; Helliwell and Waterhouse (2003) Methods 30: 289-295, and U.S. Patent Publication. N °: 20030180945, whose contents are incorporated in this document as a reference. The expression cassette for interfering with hRNA can also be designed such that the sequence oriented in the sense of the reading frame and the antisense sequence do not correspond to the endogenous RNA. In this case, the sequence oriented in the direction of the reading frame and the antisense sequence flank a loop sequence comprising a nucleotide sequence corresponding to all or part of the endogenous messenger RNA of the gene of interest. Therefore, it is the region of the loop that determines the specificity of the RNA interference. See, for example, WO 02/00904, incorporated herein by reference. The amplicon expression cassettes comprise a sequence derived from a plant virus that contains all or part of the gene of interest but in general not all genes of the native virus. The viral sequences present in the transcription product of the expression cassette allow the transcription product to direct its own replication. The transcripts produced by the amplicon can be oriented in the sense of the reading frame or antisense in relation to the sequence of interest (ie, the messenger RNA of the histidine kinase). Methods for using amplicons in inhibiting the expression of endogenous plant genes are described, for example, in Angeli and Baulcombe (1997) EMBO J. 16: 3675-3684, Angeli and Baulcombe (1999) Plant J. 20: 357- 362, and in U.S. Pat. No. 6,646,805, the contents of which are incorporated herein by reference. In some examples, the polynucleotide expressed by the expression cassette of the invention is catalytic RNA or possesses a specific ribozyme activity of the histidine kinase messenger RNA. Accordingly, the polynucleotide causes the degradation of endogenous messenger RNA, resulting in reduced expression of histidine kinase. This method is described, for example, in U.S. Pat. No. 4,987,071, incorporated herein by reference. In some examples of the invention, inhibition of the expression of one or more histidine kinases can be achieved by interference with RNA by expression of a gene encoding a microRNA (mRNA). The ARNmi are agents regulators consisting of approximately 22 ribonucleotides. MiRNAs are highly effective in inhibiting the expression of endogenous genes. See, for example Javier et al. (2003) Nature 425: 257-263, the content of which is incorporated herein by way of reference. For interference with miRNA, the expression cassette is designed to express an RNA molecule that is modeled on an endogenous miRNA gene. The mRNA gene encodes an RNA that forms a hairpin structure containing a sequence of 22 nucleotides that is complementary to another endogenous gene (target sequence). For the suppression of histidine kinase expression, the 22 nucleotide sequence is selected from a sequence of the histidine kinase transcript and contains 22 nucleotides of said histidine kinase sequence oriented in the sense of the reading frame and 21 nucleotides of a corresponding sequence. antisense that is complementary to the sequence oriented in the sense of the reading frame. RNAi molecules are highly effective in inhibiting the expression of endogenous genes and interference with inducing RNA is inherited by subsequent generations of plants. In one example, the polynucleotide encodes a zinc finger protein that binds to a gene encoding a corn histidine kinase, resulting in reduced expression of the gene. In particular examples, the zinc finger protein binds to a regulatory region of a histidine kinase gene. In other examples, the zinc finger protein binds to a messenger RNA that encodes a histidine kinase polypeptide and prevents its translation. Methods for selecting sites for zinc finger protein targeting were described, for example, in U.S. Pat. N °: 6,453,242, and methods for using zinc finger proteins to inhibit the expression of genes in plants they are described, for example, in U.S. Patent Publication. N °: 20030037355; whose content is incorporated in this document as a reference. In some examples of the invention, the polynucleotide encodes an antibody that binds to at least one corn histidine kinase and reduces the histidine kinase activity of the histidine kinase protein. In another example, antibody binding results in increased turnover of the antibody-histidine kinase complex by cellular quality control mechanisms. The expression of antibodies in plant cells and the inhibition of molecular pathways by expression and binding of antibodies to proteins in plant cells are well known in the art. See, for example, Conrad and Sonnewald (2003) Nature Biotech. 21: 35-36, incorporated herein by reference. In some examples of the present invention, histidine kinase activity is reduced or eliminated by interrupting the gene encoding said histidine kinase. The gene encoding the histidine kinase can be disrupted using any method known in the art. For example, in one case, the gene is interrupted by transposon labeling. In another example, the gene is interrupted by mutagenesis of maize plants by random or directed mutagenesis and the selection of plants showing a reduction of histidine kinase activity, histidine kinase protein levels and / or protein levels. Histidine kinase mRNA. In one example of the invention, labeling with transposons is used to reduce or eliminate the histidine kinase activity of one or more histidine kinases. Transposon labeling comprises the insertion of a transposon into an endogenous histidine kinase gene to reduce or eliminate expression of the histidine kinase. The term "histidine kinase gene" refers to the gene encoding a histidine kinase according to the invention. In this embodiment, the expression of one or more histidine kinase polypeptides is reduced or eliminated by inserting a transposon into a regulatory region or coding region of the gene encoding the histidine kinase polypeptide. A transposon that is within an exon, intron, 5 'or 3' untranslated sequence, a promoter or any other regulatory sequence of the histidine kinase gene can be used to reduce or eliminate the expression and / or activity of the histidine polypeptide encoded kinase. Methods of labeling transposons of specific genes in plants are well known in the art. See, for example, Maes ef al. (1999) Trends Plant Sci. 4: 90-96; Dharmapuri and Sonti (1999) FEMS Microbiol. Lett. 179: 53-59; Meissner et al. (2000) Plant J. 22: 265-274; Phogat et al. (2000) J. Biosci. 25: 57-63; Walbot (2000) Curr. Opin. Plant Biol. 2: 103-107; Gai et al. (2000) Nucleic Acids Res. 28: 94-96; Fitzmaurice et al. (1999) Genetics 153: 1919-1928). In addition, the TUSC process for selecting Mu selected gene insertions is described in Bensen et al. (1995) Plant Cell 7: 75-84; Mena ef al. (1996) Science 274: 1537-1540 and U.S. Patent Application Ser. No.: 5,962,764, the contents of which are incorporated herein by reference. There are other methods for decreasing or eliminating the expression of endogenous genes in plants which are also known in the art and which can be applied similarly to the present invention. These methods include other forms of mutagenesis, such as mutagenesis induced by ethyl methanesulfonate, suppressive mutagenesis, and deletion mutagenesis with rapid neutron irradiation used in a reverse gene orientation oriented in the sense of the reading frame (with PCR) to identify lines of plants in which suppressed the endogenous gene. For examples of these methods see Ohshima et al. (1998) Virology 243: 472-481; Okubara er al. (1 994) Genetics 137: 867-874; and Quesada et al. 2000, 1 54 and 421; whose contents are incorporated in this document as a reference. further, a rapid and automated method for tracing chemically induced mutations, the TILLING (Targeting Induced Local Lesions In Genomes) method, which employs denaturing HPLC or selective endonuclease digestion of products selected from a PCR is also applicable in the pre invention. See McCallum et al. (2000) Nal Biotechnol. 18: 455-457, incorporated herein by way of reference). Mutations that affect gene expression or that interfere with function (eg, histidine kinase activity or fosforele activity) of the encoded protein are well known in the art. Insertion mutations in the exons of the genes usually result in null mutants. Mutations in the conserved residues of the sites are particularly effective in inhibiting the histidine kinase activity of the encoded protein. In addition, mutations in the histidine and aspartate residues that are related to the fosforele function are also effective in inhibiting the activity of hybrid histidine kinases. The conserved residues of the active site of the plant histidine kinases have already been described suitable for a mutagenesis in order to eliminate the histidine kinase activity and those that are necessary for the phosforele function. See, for example, Hwang er al. (2002) Plant Physiol. 129: 500-51 5. Said mutants can be isolated according to well-known procedures and the mutations can be stacked at different histidine kinase loci by genetic crossing. See, for example, Gruís er al. (2002) Plant Cell 14: 2863-2882.

In another example of this invention, dominant mutants can be used to cause RNA silencing due to gene reversal and recombination of a duplicated genetic locus. See, for example, Kusaba et al. (2003) Plant Cell 15: 1455-1467. The invention encompasses additional methods for reducing or eliminating the activity of one or more histidine kinases. Examples of other methods for altering or mutating a genomic nucleotide sequence in a plant are known in the art and include, by way of example, the use of RNA: DNA vectors, RNA vectors: mutation DNA, repair vectors of RNA: DNA, mixed double oligonucleotides, self-complementary RNA: DNA oligonucleotides and recombinogenic oligonucleobases. Such vectors and methods of use are known in the art. See, for example, U.S. Pat. No. 5,565,350; 5,731,181; 5,756,325; 5,760,012; 5,795,972; and 5,871,984; whose contents are incorporated in this document as a reference. See also, WO 98/49350, WO 99/07865, WO 99/25821 and Beetham et al. (1999) Proc. Nati Acad. Sci. USA 96: 8774-8778; incorporated in this document as a reference. For the purposes of the present invention, unless indicated otherwise or which is evident from the context, a "subject plant" or "subject plant cell" is one in which a genetic alteration has been effected, such as a transformation, as in a gene of interest, or is a plant or plant cell that descends from a plant or plant cell altered in that way and that comprises said alteration. A "control" or a "control plant" or a "control plant cell" provides a reference point for measuring changes in said subject plant or plant cell.

A control plant or a control plant cell may comprise, for example: (a) a wild-type plant or plant cell, ie, of the same genotype as the initial material for the genetic alteration that resulted in the subject plant or plant cell subject; (b) a plant or plant cell of the same genotype as the initial material but which has been transformed with a null construct (ie, with a construct that has no effect on the characteristic of interest, such as a construct comprising a marker gene ); (c) a plant or plant cell that is a non-transformed segregant between the progeny of said subject plant or subject plant cell; (d) a plant or plant cell genetically identical to the subject plant or subject plant cell but which was not exposed to the conditions or stimuli that would induce the expression of the gene of interest; or (e) the subject plant itself or subject plant cell, under conditions in which the gene of interest is not expressed. For example, various examples of the present invention could measure changes in histidine kinase activity, histidine kinase levels, cytokinin response, cytokinin perception, and / or changes in one or more characteristics such as time of flowering, seed formation, branching, senescence, stress tolerance or root mass, by comparison of the subject plant or subject plant cell with the control plant or control plant cell. In certain examples the polynucleotides of the present invention can be stacked with any combination of polynucleotide sequences of interest in order to create plants with the desired phenotype. For example, the polynucleotides of the present invention can be stacked with any other polynucleotide that encodes a polypeptide with pesticidal and / or insecticidal activity, such as other toxic Bacillus thuringiensis proteins (described in US Pat.

US Patents No. 5,366,892; 5,747,450; 5,737,514; 5,723,756; 5,593,881; and Geiser ef al. (1986) Gene 48: 109; lectins (Van Damme et al. (1994) Plant Mol. Biol. 24: 825, pentin (described in U.S. Patent No. 5,981,722) and the like Generated combinations can also include multiple copies of either among one or more of the polynucleotides of interest The polynucleotides of the present invention can also be stacked with any other gene or combination of genes to produce plants with various combinations of desired characteristics including, by way of example, the desirable characteristics for foods for animals as genes for a high oil content (e.g., U.S. Patent No.: 6,232,529); balanced amino acids (eg, hordothionines (U.S. Patent Nos .: 5,990,389; 5,885,801; 5,885,802; and 5,703,409); lysine-rich barley (Williamson et al. (1987) Eur. J Biochem. 165: 99-106; and WO 98/20122), and methionine-rich proteins (Pedersen et al. (1986), J Biol. Chem. 261: 6279; Kiriyahara et al. (1988) Gene 71: 359; and Musumura et al. (1989) Plant Mol. Biol. 12: 123)); increased digestability (eg, modified storage proteins (U.S. Patent Application Number: 10 / 053,410, filed November 7, 2001); and thioredoxins (U.S. Patent Application No. 10) / 005,429, filed December 3, 2001)), the contents of which are incorporated herein by reference. The polynucleotides of the present invention can be stacked with any gene or combination of genes, and the combinations generated can include multiple copies of one or more of the polynucleotides of interest. The desired combination may affect one or more features; that is, certain combinations can be created to modulate gene expression that affects the activity of cytokinins. The modulation of cytokinin sensory activity provided by the present application can be combined with methods and constructs for modulating cytokinin levels, such as those described in co-pending US Pat. N °: 60 / 610,656, 60 / 637,230 and 60 / 696,405; 1 1 / 094,917; 10 / 817,483; and 09 / 545,334, incorporated herein by reference; and in U.S. Patent Publication. No. 2003/0074698 (Schmulling et al.) And U.S. Pat. No. 6,617,497 (Morris). The polynucleotides of the present invention can also be stacked with desirable characteristics for resistance to diseases or herbicides (eg, fumonisin detoxification genes (U.S. Patent No. 5,792,931), avirulence and resistance genes. to diseases (Jones et al. (1994) Science 266: 789; Martin et al. (1993) Science 262: 1432; Mindrinos et al. (1994) Cell 78: 1089); mutants of acetolactate synthetase (ALS) leading to herbicide resistance, such as S4 and / or Hra mutations, glutamine synthetase inhibitors such as phosphinothricin or basta (for example, the bar gene), and resistance to glyphosate (EPSPS gene)); and desirable characteristics for processing products or processes such as high oil content (e.g., U.S. Patent No.: 6,232,529); modified oils (e.g., fatty acid desaturases genes (U.S. Patent No. 5,952,544; WO 94/1 1516)); modified starches (for example, ADPG pyrophosphorylases (AGPase), starch synthetase SS), starch branching enzymes (SBE) and starch debranching enzymes (SDBE)); and polymers or bioplastics (e.g., U.S. Patent No. 5,602,321, beta-ketothiolase, polyhydroxybutyrate synthetase, and acetoacetyl-CoA reductase (Schubert et al (1988) J. Bacteriol., 170: 5837-5847). they facilitate the expression of polyhydroxyalkanoates (PHA)), the contents of which are incorporated herein by reference. You could also combining the polynucleotides of the present invention with polynucleotides that affect agronomic characteristics, such as male sterility (e.g., see U.S. Patent No. 5,583,210), stem strength, flowering time or characteristics of transformation technology such as cell cycle regulation or gene targeting (eg, WO 99/61619; WO 00/17364; WO 99/25821), the contents of which are incorporated herein by reference. These stacked combinations can be created by any method, including for example, crossing plants with any conventional methodology or TopCross or genetic transformation. If the characteristics were stacked by genetic transformation of the plants, the polynucleotide sequences of interest can be combined at any time and in any order. For example, a transgenic plant comprising one or more of the desired characteristics may be used as a target to introduce other characteristics through a subsequent transformation. The characteristics can be introduced simultaneously into a cotransformation protocol with the polynucleotides of interest provided by any combination of transformation cassettes. For example, if two sequences are introduced, the two sequences may be contained in separate transformation cassettes (trans) or they may be contained in the same transformation cassette (cís). The expression of the sequences of interest can be directed by the same promoter or by different promoters. In certain cases, it may be desirable to introduce a transformation cassette which will suppress the expression of the polynucleotide of interest. This can be accompanied by any combination of other suppression cassettes or overexpression cassettes to generate the desired combination of characteristics in the plant. Is considered in addition that the polynucleotide sequences can be stacked at the desired genomic location using a site-specific recombination system. See, for example, W099 / 25821, W099 / 25854, WO99 / 25840, W099 / 25855 and W099 / 25853; also US Patents Nos .: 6,552,248, 6,624,297, 6,573,425, 6,455,315 and 6,458,594, the contents of which are incorporated herein by reference. In addition, two protein coding regions can be operably linked in the same reading frame to produce a fusion protein. Some modifications can be made to facilitate the cloning, expression or incorporation of a fusion protein. Such modifications are well known to those skilled in the art and include, for example, the addition of a methionine at the amino terminus to provide a start site or additional amino acids (eg, poly His) at both ends to create sequences of purification in convenient locations. You can also enter restriction sites or termination codons. Expression of heterologous DNA sequences in a plant host depends on the presence of operatively linked regulatory elements that are functional within the plant host. The choice of the promoter sequence will determine when and where within the plant that the heterologous DNA sequence will be expressed. When continuous expression is desired in all the cells of a plant, constitutive promoters are used. Conversely, when gene expression is desired in response to a stimulus, inducible promoters are the regulatory element of choice. If an expression is desired in specific tissues or organs, promoters are preferably tissue-based. That is, these promoters can direct expression in specific tissues or organs. Other 5 'regulatory sequences may be included and / or 3 'with respect to the central promoter sequences in the expression cassettes of the transformation vectors to obtain variable levels of expression of the heterologous nucleotide sequences in a transgenic plant. See, for example, U.S. Pat. N °: 5,850,018. Regulatory sequences may also be useful for controlling a temporal and / or spatial expression of endogenous DNA. Some examples of the invention comprise nucleotide sequences that favor the initiation of transcription in specific tissues, including the vascular tissue and the meristematic tissue of roots and / or shoots, and in callus tissue. An example of a promoter region sequence of a histidine kinase of the present invention, AtCKI2, is shown in SEQ ID NO: 29. A "promoter" refers to a regulatory DNA region that usually comprises a TATA box capable of directing RNA polymerase II to initiate RNA synthesis at the appropriate transcription initiation site for a particular coding sequence. A promoter may further comprise other recognition sequences generally located 5 'to the TATA box, called 5' promoter elements, which affect the rate of transcription initiation. If it is considered that having identified the nucleotide sequences for the promoter region described herein, the isolation and identification of other regulatory elements in the 5 'untranslated region located 5' to the region belongs to the state of the art. particular promoter identified herein. Therefore, the promoter region described herein is generally defined as comprising 5 'regulatory elements, such as those responsible for a preferred tissue expression and temporally preferred coding sequence, enhancers and the like. In the same way, the promoter elements that allow expression in the desired tissue can be identified, isolated and used with other nuclear promoters to confirm expression with preference for tissues. Promoter elements can also be identified and isolated for use with other nuclear promoters. The term "operably linked", as used herein, includes reference to a functional linkage between a promoter and a second sequence, wherein said promoter sequence initiates and intervenes in the transcription of the DNA corresponding to the second sequence. Generally, operably linked means that the nucleic acid sequences are linked contiguously and, when necessary, they are linked to two regions that encode proteins that are contiguous and are in the same reading frame. An endogenous promoter is operably linked to the endogenous coding region that it regulates. The term "tissue-preferred" promoter refers to a sequence that preferentially initiates transcription in certain tissues, such as leaves, roots or seeds. The promoter with preference for tissues may also direct expression in certain tissue types in one or more organs; for example, in vascular tissues of roots or leaves. The isolated promoter sequence of the present invention can be modified to provide a range of expression levels of the heterologous nucleotide sequence. It can be used less than the entire promoter region and still retain the ability to direct an expression with preference for tissues. However, it is considered that it is possible to decrease the levels of mRNA expression with the deletion of portions of the promoter sequence. Therefore, the promoter can be modified to be a weak or strong promoter. Generally, a promoter that drives the expression of a coding sequence at a low level is proposed as a "weak promoter". A level "low" refers to levels between approximately 1 / 10,000 transcripts and approximately 1 / 100,000 transcripts and approximately 1 / 500,000 transcripts., a strong promoter directs the expression of a coding sequence at a high level or at levels between about 1/0 transcripts and about 1/100 transcripts and about 1/1000 transcripts. In general, at least about 20 nucleotides of an isolated promoter sequence will be used to direct the expression of a nucleotide sequence. It is considered that to increase the levels of transcription, enhancers can be used in combination with the promoter regions of the invention. Enhancers are nucleotide sequences that act by increasing the expression of a promoter region. Enhancers are known in the art and include the region of enhancer SV40, enhancer element 35S and the like. The fragments of the promoter nucleotide sequence described herein are also encompassed by this invention. Said fragments will comprise at least about 20 contiguous nucleotides, preferably at least about 50 contiguous nucleotides, more preferably at least about 75 contiguous nucleotides, even more preferably at least about 100 contiguous nucleotides of the promoter nucleotide sequence as described herein. Said fragments will usually comprise the TATA recognition motif of the promoter sequence. Such fragments can be obtained using restriction enzymes to clivate the natural promoter nucleotide sequences described herein.; synthesizing a nucleotide sequence by using PCR technology. See in particular, Mullis et al. (1987) Methods Enzymol. 155: 335-350 and Erlich, ed. (1989) PCR Technology (Stockton Press, New York). Said fragments include, for example, sequences capable of directing an expression with preference for tissues, elements responsible for temporal or tissue specificity, elements that respond to a phytohormone and sequences useful as probes to identify similar sequences. Biologically active variants of the promoter sequence are also comprised in the composition of the present invention, including variants due to site-directed mutagenesis. A regulatory "variant" is a modified form of a regulatory sequence in which one or more bases have been modified, deleted or added. For example, a common way of removing part of a DNA sequence is to use an exonuclease in combination with DNA amplification to produce unidirectional nested deletions of double-stranded DNA clones. There is a commercial item set for this purpose that is sold under the Exo-Size ™ trade name (New England Bíolabs, Beverly, Mass.). Briefly, this method comprises the incubation of exonuclease III with DNA to progressively remove the nucleotides in the 3 'to 5' direction in the 5 'overlays, cohesive ends or nicks in the DNA annealing. However, exonuclease III can not remove the nucleotides in the superpositions of 4 3 'bases. The timed digestion of a clone with this enzyme produces unidirectional nested deletions. An example of a regulatory sequence variant is a promoter formed by one or more deletions in a larger promoter. It is possible to suppress the 5 'portion of a promoter to the TATA box near the transcription initiation site without canceling the promoter activity, as described by Zhu et al., The Plant Cell 7: 1681 -89 (1995). Said variants should retain the promoter activity, in particular the ability to direct expression in specific tissues. The promoter activity can be measured by Northern blot analysis, measurements of reporter activity when using transcriptional fusions and the like. See, for example, Sambrook ef al. (1989) Molecular Cloning: A Laboratory Manual (2nd ed. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.), incorporated herein by reference. The nucleotide sequence for the promoter of the invention, as well as fragments and variants thereof, can be provided in expression cassettes together with heterologous nucleotide sequences for expression in the plant of interest, more particularly in specific tissues of the plant . Said expression cassette is provided with a plurality of restriction sites to insert the nucleotide sequence under the transcription control of the promoter. These expression cassettes are useful for genetic manipulation of any plant in order to obtain the desired phenotypic response. This can be achieved by increasing the expression of endogenous or exogenous products in the specific tissues of interest. Alternatively, the expression of one or more endogenous products, in particular enzymes or cofactors, can be reduced. The promoter region of the invention can be isolated from any plant, including, by way of example, corn (Zea mays), cañola (Brassica napus, Brassica rapa ssp.), Alfalfa. { Medicago sativa), rice. { Oryza sativa), rye (Sécale cereale), sorghum (Sorghum bicolor, Sorghum vulgare), sunflower (Helianthus annuus), wheat (Triticum aestivum) and soybean (Glycine max). Promoter sequences from other plants can be isolated according to well known techniques based on their sequence homology with promoter sequences that are describe in the present. In these techniques, all or a portion of the promoter sequence known as a probe that will hybridize selectively with the other sequences present in a population of cloned fragments of genomic DNA (i.e., genomic libraries) of a chosen body. There are methods available in the art for hybridization of nucleic acid sequences. The following examples are offered as illustrations and should not be construed as limitations. EXAMPLE 1 Histidine kinases of Arabidopsis Signal transduction systems intervene in the perception of environmental and hormonal stimuli and the subsequent subsequent activation of appropriate cellular responses. The strategic location of these systems at the beginning of the signaling cascades makes them ideal candidates for the modulation of complex characteristics. The stimuli described by being perceived by such systems in plants include osmolarity, ethylene and cytokinin, while in bacteria they include nitrogen, phosphate and salts, and in cyanobacteria they include salts and low temperatures. A typical two-component system consists of a histidine kinase with sensory activity and a response regulator. The amino acid sequence of ZmCKI2 (SEQ ID NO: 8) is homologous to the Arabidopsis protein CKI2 (SEQ ID NO: 14) in the histidine kinase and response regulator domains, with a general sequence similarity of 55% for all the protein (GAP; BLOSUM matrix 62). The Arabidopsis CKI2 was originally isolated in a test with activation tags for the gain-of-function mutants that present a constitutive response to cytokinin in absence of the hormone (Kakimoto (1996) Science 274: 982-985). CKI2 can modulate the transduction of cytokinin signals through a unique mechanism in relation to other cytokinin receptors previously described. The protein AtCKI2 is a histidine kinase that functions as one of the components in signal transduction systems. The coding region of AtCK / 2 contains eleven introns, with an additional intron within the 5 'untranslated region. The longest open reading frame could be translated into a protein of 922 amino acid residues. The product of the translation of one of the predicted open reading frames of Oryza sativum (Os6G44410) was similar to CKI2 throughout its amino acid sequence and was called OsCA / 2 (see Figure 2 and SEQ ID N °: 23) . The AtCKI2 protein contains three regions with sequence identity with the protein domains previously described. The histidine kinases whose activity has been demonstrated contain five motifs, the boxes H, N, G1, F and G2, which are essential for phosphorylation, hydrolysis and binding to ATP (Stock et al., 2000). The histidine kinases of hybrid-type receptors contain a second region, the regulatory region of responses, which is similar to the signaling targets of prototypical cascades of two-component signal transduction. The response regulators contain four motifs that contain residues essential for phosphorylation (Stock et al., 2000). The CKI2 translation products predicted from both Arabidopsis and rice contain signature residues from the histidine kinase and regulatory regions of responses that are evident in the histidine kinases of hybrid type receptors (Figure 3A and 3B) of divergent organisms. In plants, cytokinin and ethylene receptors that respond to hormones were described as histidine kinases of hybrid type receptors (Schaller et al., 2002). However, the CKI2 protein is distinct from these hormone receptors in that they do not exhibit sequence similarity with the protein cytokinin or ethylene binding domains described for their amino terminal ends (Schaller and Bleecker, 1995; Yamada et al., 2001). In addition, the data indicates that CKI2, similar to ETR1, may contain multiple subsequent targets in the cascade. A third region was identified, near the amino terminus of CKI2, which presented sequence similarity with the PER / ANRT / SIM (PAS) superfamily of domains already described and contains signature residues that were identified in a comparison of PAS domains (Fig. 3C) (Taylor and Zhulin, 1999). There is a putative PAS nuclear sequence that is 59% identical (23 of 39 residues) to Arabidopsis and rice sequences. Three regions adjacent to the PAS domain of CKI2 were identified with a repeated motif of a hydrophobic residue and a predicted alpha-helical tertiary structure. The unique PAS type domain of CKI2 is necessary for its ability to modulate cytokinin reactivity. Based on an improved trap-line and the determination of the expression profile, CKI2 expression can respond to hypoxic growth conditions or to the application of hydrogen peroxide (Desikan et al., 2001, Baxter-Burrell et al., 2003). The existence of transcription self-regulation has been demonstrated for some bacterial and plant histidine kinases (Urao et al., 1999, Bijlsma and Groisman, 2003, Rashotte et al., 2003) and therefore CKI2 could serve as an integrator. of said environmental stimuli in the transduction of phytohormone signals. Consistent with this hypothesis, it has been shown that the PAS domains of some proteins have oxygen sensing or redox potential (Taylor and Zhulin, 1999, Gilles-Gonzalez and González, 2004). The presence of a PAS domain of type CKI2 in some cyanobacterial histidine kinases allows use these model organisms to possibly identify and characterize the CKI2 stimulus. The majority of receptor histidine kinases are located on the membrane with transmembrane regions identifiable at their terminal amino termini (West and Stock, 2001; Hwang et al. , 2002). Unlike other histidine kinases of Arabidopsis, it appears that AtCKI2 lacks the amino-terminal transmembrane regions based on prediction algorithms of structures. To provide experimental evidence of its subcellular location in vivo, constructs were created to produce an almost full length or amino terminal region of CKI2 fused in the GFP translation. Similar to the GFP control, the fluorescence of the CKI2 (5-355): GFP fusion protein was localized both in the cytosol and in the nucleus during transient expression in onion epidermal cells. In contrast, the fluorescence of a GFP fusion protein with the amino-terminal region of AHK1, AHK1 (1 -500): GFP, which contains identifiable transmembrane regions (Urao et al., 1999), was apparently localized in the membrane plasma Various qualitative similarities between the loss mutant of Arabidopsis, ck2-2, and the triple mutant cre1ahk2ahk3 (Nishimura et al. (2004) Plant Cell 16: 1365-1377) have already been observed. Root growth is affected in both, with a general reduction in the rate of root growth and alterations in the radicular architecture. The general vegetative growth had been reduced; the mutants had smaller leaves, a reduced height of the plants and a delay in the transition to reproductive development. In Arabidopsis, AtCKI2 is preferentially expressed in a manner similar to the expression domains specific for other cytokinin receptors; the tissues of roots, immature leaves and inflorescences present the levels of detectable higher expression. The endogenous transcript of CKI2 could not be detected by Northern hybridization using total RNA transfer. The use of RT-PCR allowed to amplify two adjacent regions of the 5 'coding sequence of C / 2, corresponding to the unique amino terminus of CKI2, from cDNA derived from RNA specific to roots, leaves, stems or inflorescences. When the 18S rRNA primers were used as internal controls, the cycle-dependent accumulation of the CKI2 product could be observed in a reproducible manner in fewer cycles in root and inflorescence samples, which implies the existence of a higher level of endogenous expression in these tissues. Transgenic Arabidopsis plants comprising a transcription fusion of the AtCKI2 promoter (SEQ IDN: 29), the coding region of the GUS reporter gene and the PINII transcription termination region showed a histochemical staining for GUS activity predominantly in the vasculature of immature leaves, in the vasculature of the roots, hypocotyl and in the radicular meristem. In germinating seedlings, GUS activity was only detectable 48 hours after its transfer to light with a diffuse pattern in all the cotyledons and at the root end. The region with GUS activity at the tip of the root may include the radicular meristem, but the area of elongation of the roots near the tip of the root did not show activity of the reporting gene. At 72 hours after the transfer, GUS activity appeared in the vascular bundle of the root, within regions that presumably had completed their cell differentiation (Scheres et al., 2002). In addition, GUS activity became more evident in the vasodilatation of the cotyledons and was observed in the shoot meristem and adjacent hypocotyl. The spatial activity of GUS at the tip of the root was summarized in the development of lateral roots; the GUS activity it was evidenced first by all the primordium but then it was restricted to the distal tip and to the vascular bundle near the main root. Although it was not detectable in the leaf emerges, the activity of the PROCKI2: GUS transgene was observed diffusely in all leaf tissue, including the vasculature, in the early stages of development. The activity was detectable in the floral meristem and was observed diffusely in all the floral organs, being more pronounced in the vasculature. Within the gynoecium, GUS activity was not observed for a short period in the anthesis and was not detectable in ovules, developing seeds or in embryos. The expression at the tip end of the C / 2 root appears to be quite different from the expression of other Arabidopsis histidine kinases. This is especially interesting since it has been shown that this region is a site of accumulation of both cytokinin and auxin according to immunolocalization analysis and with informant genes (Scheres et al., 2002, Aloni et al., 2004). Therefore, CKI2 is not present during the primary events of organogenesis, which excludes its participation in a developmental role, but is expressed in regions of hormone integration and can serve as a cellular constituent to participate in the perception of such stimuli. . Among the response regulators examined, the unique expression pattern at the tip of the CKI2 root is only shared by ARR5 (D'Agostino et al., 2000, Aloni et al., 2004). In the absence of other two-component receptors in this region, CKI2 could serve as a primary initiator of two-component signal transduction, resulting in activation of the transcription of ARR5. In other types of tissue, such as meristems and shoot vasculature, for which the expression of Many histidine quasase receptors, signaling two components could be modulated with any of the described receptors. This pattern of GUS expression in cells in active division is consistent with the function of CKI2 in the cytokine sensor activity. The vascular location of GUS expression directed by the AtCKI2 promoter is similar to that of AtCREI, AHK2 and AHK3, all of which are known for their participation in cytokinin sensing activity, as demonstrated by Higuchi et al. ((2004) Proc. Nati. Acad. Sc., USA 1 01: 8821 -8826; and Nishimura et al. ((2004) Plant Cell 1 6: 1 365-1 377). ZmCKI2 localization studies in immature maize cob tissues showed a clear expression of ZmCKI2 in the vascular bundles, which again implies a role of cytokinin sensory activity during the transport of the hormone through the vascular bundles. The activity of PROCK GUS was also evaluated in response to the exogenous application of hormones in both seedlings and callus tissue. Five-day seedlings were incubated in the presence of either cytokinin or auxin and stained to observe GUS activity. Based on the trials with various concentrations of GUS substrate, it did not appear that the spatial or quantitative activity of the transgene was affected by a period of hormone treatment of either one or three hours. To examine the chronic exposure to the application of hormones, hypocotyl segments of transgenic PROcw'GUS were grown in darkness on a callus-inducing medium (MIC). In the seedlings grown in the dark with five days of growth, the activity in the regions of the tip of the root and the shoot meristem was similar to the seedlings cultivated with light. However, the GUS activity was relatively diffuse within the cotyledons, it was only evident in the region adjacent to the meristem within the hypocotyl and was not detectable in the hypocotyl vasculature or in the root. The hypocotyls were trimmed and after seven days of growth on MIC, the GUS activity was evident in the vasculature of the entire hypocotyl, as well as in small foci that apparently correlated with tissue proliferation regions. Next, the hypocotyl segments were transferred to various proportions of cytokinin to auxin and then the activity was evaluated at seven, fourteen and twenty-one days. The GUS activity was similar with each of the hormone treatments throughout the course and recalled the observable activity in plant. Although not observed in developing bud tissue, GUS activity was evident at the apex of the root and in the vascular bundle, except in the region immediately adjacent to the root meristem, from individual developing roots. AtCKI2 can also interact with the two-component canonical signaling intermediates as evidenced by the two yeast hybrid assays. The two-hybrid assay in heterologous yeast has been used successfully to identify the signaling targets of Arabidopsis histidine kinases (Urao et al., 2000) and this assay was used to define the CKI2-dependent signaling cascades. The details of the assay will be described later in Example 4. Fragments of the CKI2 coding sequence, which contain either the amino terminus and PAS, or the histidine kinase and response regulator regions (both in combination and individually), to the GAL4 DNA binding domain (GAL4BD) of the coding sequence for use in a two hybrid assay. Among all the fusion proteins examined (six in total), only one (GAL4BD: CKI2 (590-922) produced positive colonies from the primary test that were reassessed successfully in auxotrophic and colorimetric growth assays.

Clones representing two independent genes, PROTEIN 3 FROM PHOSPHOTRANSFERENCE OF ARABIDOPSIS HISTIDINE (AHP3, At5G39340) and At3G28690, a putative serine / threonine protein kinase, were identified from the library with GAL4BD: CKI2 (590-922). AHPs are the signaling targets described for canine receptor histidine kinases, such as CRE1, AHK1 and ETR1 (Grefen and Harter, 2004). The full-length proteins of four AHPs that can be obtained were then evaluated and showed auxotrophic and histidine colorimetric positive activity, which indicates that AtCKI2 could interact with each of these proteins and also support the role of this histidine kinase in the proteins. Two-component signal transduction cascades. The At3G28690 is homologous of PROTEIN KINASE 1 OF ARABIDOPSIS (APK1) (Hirayama and Oka, 1992) and APK2 (Ito et al., 1997) previously published and is called APK3. The original test allowed us to identify a fusion of truncated proteins APK3, APK3 (262-476), which only contains a part of the canonical kinase domain and the carboxyl terminal region. When comparing the results with this truncation, the fusion proteins with either full-length APK3 or a second truncated protein, APK3 (15-476), failed to interact positively with GAL4BD: CKI2 (590-922) in the two-assay hybrids This suggests that its amino terminus may interfere with the interaction of CKI2. This observation could be due to the presence of a self-inhibitory domain, as shown for the unrelated SOS2 protein kinase (Zhu, 2002). The APK3 has been classified as a Cytoplasmic Receptor-like Kinase (RLCK) VI I (Family 1 .2.2) in Arabidopsis. See Purdue University website on Functional Genomics of Plant Phosphorylation (plantsp.qenomics.purdue.edu) Preliminary experiments suggest that endogenous APK3 is expressed at a level relatively low Its use continues in the modulation of cytokinin-dependent growth responses by transgenic and mutant analyzes. The first insertion allele of CKI2, ck2-2, was identified in a test for cytokinin-independent growth phenotypes of callus tissue labeled for activation. The Cki2-1 calluses could produce shoot tissue in the absence of exogenous cytokinin, but this phenotype was not observed in the progeny of the regenerated plants (Kakimoto, 1996, 1998). The T-DNA of cki2-1 was inserted into the 5 'region of the coding sequence, which would likely produce a truncated mRNA expressed constitutively, where the translation product lacked the 84 amino terminal amino acid residues (CKI2 ( 85-922)) (Kakimoto, 2002). A T-DNA insertion line, designated cki2-2 in the present, was characterized as a mutant putative cki2 allele. The left border of the T-DNA insert could be amplified by PCR, and the hemizygous plants backcrossed twice with wild-type Arabidopsis (Columbia Access). An evident mutant phenotype (see its description below) cosegregated with plants that were homozygous for T-DNA insertion. The segregation ratio of the mutant phenotype, 4.2: 1 (wild type: mutant), had been deviated in relation to the expected ratio of 3: 1 (Chi square test, p = 0.05) for a recessive mutant allele of a only gene, which could be due to a little penetrating negative effect on the development of the gametophyte. The lack of observable GUS activity in female sporophytic or gametophytic tissue suggests that these defects may be limited to the development of stamens or pollen. The left border of the allele insertion site c / a'2-2 is located within the eleventh exon of CKI2 (Figure 4A). This insertion site, confirmed using cDNA derived from ck2-2, would result in a translation product in which the 53 carboxyl terminal residues of the endogenous CKI2 had been replaced by 33 residues derived from the left border of the T-DNA. Two critical motifs for the formation of the active site of phosphorylation of the regulatory domain of responses (Figure 3) in the translation product cki2-2 would have been lost. Northern hybridizations and RT-PCR indicate that the expression of the flanking coding sequence (At5G10730) did not appear to be affected in cki2-2. Southern hybridization of the genomic DNA of cki2-2 with a 35S promoter fragment of the cauliflower mosaic virus, which is contained in the T-DNA of pROK2 (Baulcombe et al., 1986), suggested that an insertion had occurred. in tandem within the CKI2 coding sequence. Therefore, although it was possible that cki2-1 was not affected in terms of protein function, cki2-2 represents a functional null allele with respect to the response regulating activity. However, the cki2-2 protein can retain the histatin kinase activity and the partially functional protein can still affect the subsequent signaling pathways. The ability of the ETR1 region of the histidine kinase to function as an independent domain (Gamble et al., 1998) and the phenotypic differences observed in the mutant versions of histidine kinase or regulatory responses of CKI 1 in protoplast assays (Hwang and Sheen, 2001) support this proposal. In addition, Nakamura et al. (1999) demonstrated that the regulatory domain of CKI 1 responses could facilitate the trans-dephosphorylation of two AHP proteins and that the regulatory domains of some bacterial histidine kinases are essential to define the specificity of protein interaction or regulation of the histidine kinase activity (Bijlsma and Groisman, 2003). It is very feasible that insertion mutants cki2 affect in a different to cytokinin signaling through one of these mechanisms. Since these potential effects would take place after translation, probably no detectable differences are observed in the expression of the reporter gene, such as ARR6 inducible by cytokinin. The mutant phenotype ck2-2 could be described as a general reduction in the rate of plant growth and development. The Ck2-2 seedlings could be identified on the basis of a light green color in relation to the wild type, which was evident throughout its life cycle. The flowering time had been prolonged in the cki2-2 plants, where the transition to flowering took place 12-1 5 days after the wild type, although the amount of vegetative leaves present during the transition (approximately twelve) was the same. The mature cki2-2 plants showed a reduction both in size and height, with an average of 25% of the length of the primary bud of wild type, and showed an evident decrease in the internodal elongation. On the basis of the growth of seedlings on plates, the root growth of cki2-2 was reduced in relation to the wild type. The onset of lateral roots seemed to be temporarily delayed in the mutant; however, unlike the wild type, the growth of primary adventitious roots could exceed that of the main root axis during the early stage of development. No major morphological defects were observed in the root, vegetative or floral organs of cki2-2 and the skotomorphonic or etiolated response of the cki2-2 seedlings grown in the dark had not been altered. AtCKI2 had previously been associated with hormone signal transduction based on a line marked by activation, and current observations suggest a certain overlap of expression domains with the described cytokinin receptors. To evaluate the differences in the answers hormone-dependent, cki2-2 seedlings were evaluated for their physiological and molecular responses to the cytokinin benzyladenine (BA) and to the auxin indoleacetic acid (IAA). Primary radicular growth is inhibited in wild-type plantlets in response to increasing concentrations of cytokinin and auxin (Inoue et al., 2001); these phenotypic responses were also observed in cki2-2 seedlings. However, due to the relatively reduced root growth of cki2-2, this effect was less pronounced. The activation of hormone-dependent transcription of specific genes induced by cytokinin and auxin was analyzed (D'Agostino et al., 2000, Hagen and Guilfoyle, 2002), ARR6 and IAA5 respectively, in both wild type and cki2-2 . Wild-type and ck2-2 seven-day seedlings were treated with BA or IAA, and hormone-dependent induction of reporter gene expression could be observed with semi-quantitative RT-PCR. The results indicate that cki2-2 seedlings respond to the exogenous application of cytokinin and auxin in physiological and molecular assays in plant, which suggests that the loss of CKI2 activity does not completely nullify the ability of the plant to perceive these hormones . Individual mutants of the cytokinin hormone receptors, CRE1 and AHK3, do not present large morphological defects when cultured under normal growth conditions but are demonstrably hyposensitive to cytokinin in callus growth assays (Inoue et al., 2001; Ueguchi et al. al., 2001; Higuchi et al., 2004; Nishimura et al., 2004). To further explore this observation, an AHK3 T-DNA insertion line, designated ahk3-4 (Figure 4B) was obtained herein, and transgenic lines were created that constitutively expressed the full-length coding sequence AHK3 with the promoter of UBIQUITINA de Zea mays (PROUBQ) - Se confirmed the exonic location of the T-DNA of ahk3-4 and the constitutive expression of the transgenic lines was demonstrated using Northern hybridization. Duplicate, independent samples of hypocotyl tissue were cut from wild type, mutant or transgenic Arabidopsis lines (wild type, ahk3-4, PROUBQ: AHK3, ahk1 -1, PROUBO: AHK1, cki2-2, PROUBQ: CKI2, PROUBQ : CKI2 (1 -363) and PROUBQ: CKI2 (353-922)) and were cultured on plates containing different proportions of cytokinin: auxin. The following trans-zeatin concentrations were used in the gradient: 0.0; 0.01; 0.05; 0.1; 0.5; 1.0 pg / ml with 0.2 pg / ml indolebutyl acid. The plants of the mutant and transgenic lines did not present any evident morphological defect under normal growth conditions. Under the callus growth conditions evaluated, no significant differences were observed in root formation between calluses derived from the wild type, mutant and transgenic. On the contrary, differences were observed in the formation of shoots during the growth of the callus tissue in relation to the wild-type callus. With a constant concentration of auxins, the callus ahk3-4 required a higher concentration of cytokinin than the wild-type callus to produce a verdure of tissues and formation of significant shoots. Conversely, the constitutive expression of AHK3 resulted in green callus tissue and formation of shoots at a lower concentration of cytokinin relative to the wild type was initiated. Accordingly, the relative level of expression of functional AHK3 may affect some of the callus tissue responses to the exogenous cytokinin application but would not appear to alter the development of the plants due to endogenous cytokinin levels.

We determined the effects of altering the endogenous expression of histidine kinase? ?? , which lacks the described CHASE domain of cytokinin binding, in hypocotyl growth assays to serve as a potential negative control. It has been suggested that AHK1 functions as an osmosensor in Arabidopsis (Urao et al., 1999), possibly as a constitutively active histidine kinase, and would not hypothetically affect cytokinin-dependent callus growth. An ahkl mutant, indicated as ahk1-1 in the present (Figure 4C), was identified by examining a population of T-DNA insertion lines. Transgenic PROUBQ-'AHK1 lines were created and selected based on the detectable expression of the transgene by Northern hybridization. As with the histidine kinase of AHK3 receptors, no significant morphological defects were observed in the mutant and transgenic lines under normal growth conditions. Similarly, in the callus growth assay, the hormone-dependent growth of mutant callus ahk 1-1 and transgenic callus PROUBQ AHKI could not be differentiated from wild-type callus. These results suggest that alterations in the endogenous expression of AHK1 do not affect, in a positive or negative way, the growth of callus, which shows that not all the histidine kinases of Arabidopsis can modulate the capacity of response to cytokinin. In similar experiments, the ability of CKI2 to affect callus growth was examined. Transgenic lines were created that constitutively express the C / 2 genomic coding sequence, confirmed by Northern hybridization. These lines did not show evident morphological or growth defects under normal conditions.

Cultured callus tissue of these mutant ck2-2 and transgenic PROUBQ 'CKI2 lines was plated on plates containing increasing proportions of cytokinin to auxin. In general, the callus tissue of cki2-2 appeared to be less prolific than the wild type. Similar to the mutant callus ahk3-4, it appeared to be hyposensitive to cytokinin concentration based on tissue greenness and shoot formation. The constitutive expression of CK / 2 resulted in the growth of callus that appeared to be hypersensitive to cytokinin, but relatively less pronounced than the transgenic PROUBQ: AHK3. To further explore the positive growth effects of CKI2 expression, the transgenic tissue expressing either the amino terminal coding sequences and SBP was evaluated. { PROUBQ: A T-CKI2 (1-363)), OR the histidine kinase and the response regulator (PROUBQ: A T-CKI2 (353-922)), due to their differences in the growth of calluses. The expression of these two constructions did not seem to detectably affect the ability of the callus tissue to respond to hormones. Accordingly, analogous to the negative pleiotropic effects observed in normal growth conditions and similarly to the hyposensitivity of the callus ahk3-4, the corns cki2-2 are less reactive to the exogenous concentration of cytokinin than the wild type. The hypersensitive cytokinin effects of CK / 2 expression, observed only under the conditions of callus growth, are phenotypically similar to the constitutive expression of AHK3 and recall the description of the line marked for CKI2 activation (Kakimoto, 1996). This phenotype can not be duplicated with the expression of only the coding regions of histidine kinase and regulator of CKI2 responses.

EXAMPLE 2 Maize histidine kinases The ZmCKI2 polynucleotide sequence (SEQ I D N °: 7) was obtained with a rice protein homology search using the sequence of the Arabidopsis protein CKI2. A superior rice candidate was used to search the genomic sequences of maize available in the public sequence databases. To produce the ZmCKI2 polynucleotide sequence, the sequences of the partially identified 5 'and 3' ends of corn were assembled in a contig and the regions of the missing medium were filled by physical cloning using the information from the sequences of the ends. In particular, RNA was extracted from immature corn cob tissue and a pool of cDNA was prepared from the RNA using reverse transcription. The ZmCKI2 cDNA was cloned by direct PCR from this cDNA pool. The other polynucleotides of the invention encoding maize histidine kinases were obtained using a similar approach. ZmHK2, ZmHK3 and ZmCKI2 were physically cloned from the pool of the prepared cDNA with immature corn cob RNA as described above. The sequence for ZmCREI (SEQ ID N °: 1 -3) was completed by detection with BAC and displacement with primers. The genomic sequence of a selected BAC clone was sent to the Sequence Annotation Viewer and shown to contain a partial coding sequence for the 5 'end of ZmCREI. This coding sequence showed a perfect overlap with the complete insertion sequence for a selected EST encoding the 3 'end of ZmCRE I. The coding sequence identified from the BAC clone and the complete insertion sequence from the EST were assembled to obtain a full-length coding sequence for ZmCRE I.

The sequence for ZmCKH (SEQ I D N °: 26-28) was obtained based on the partial sequence information gathered by genome displacement. Based on the partial sequence information for ZmCKM identified by BLAST searches, primers were designed that allowed to amplify ubn fragment of ~ 3 kb. The confirmation of the sequence was made with around 400 bp by both ends of this sequence and, when this sequence was used in BLAST searches, a genomic fragment of 7008 bp was identified. This genomic sequence was sent to predict the cDNA to Sequence Annotation Viewer and was predicted to contain the coding sequence for ZmCKH. As observed with the Arabidopsis histidine kinase, AtCKM, the ZmCKM coding region falls within the same region as the AHK1 osmosensor (Fig 5). This sequence similarity indicates that ZmCKM could be related to the cytokinin signaling as proposed for AtCKM, or in the osmosensor as proposed for AHK1. The homology searches also revealed that the ZmCKH sequence shows similarity to cold-inducible histidine kinase from Catharanthus roseus. A partial ZmCKM cDNA was used to explore its cell-type specific expression in immature B73 ears. Similar to ZmCKI2, it was found that the expression of this gene in the ear was confined to the vasculature. The results of the paired comparisons of the amino acid sequences of the amino acid sequences ZmHK2, ZmHK3 and ZmCREI with each of the amino acid sequences of AtCRE I, AtAHK2 and AtAHK3 are shown in Table 1. The results of the paired comparisons of amino acid sequences of the amino acid sequence ZmCKI2 with each of the amino acid sequences AtCKI2 and OsCKI2 are provided in Table 2.

To determine the percent sequence identities presented in Tables 1 and 2, the amino acid sequences were aligned with GAP in paired combinations using the BLOSUM62 scoring matrix. In addition, Figure 1 provides a multiple alignment of amino acid sequences of the amino acid sequences ZmHK2, ZmHK3, ZmCKI2 and ZmCREI with other histidine kinases of hybrid type receptors. The sequence identities of Tables 1 and 2 and the relatively high level of conservation of the amino acid sequences within the five boxes of histidine kinase (H, N, G1, F, G2, see Figures 1 and 3) provide a additional support to identify the sequences of the present invention as functional histidine kinases. Table 1. Percentage amino acid sequence identities between histidine or nase s of rece to re s Table 2. Percentage amino acid sequence identities between receptor histidine kinases Still further, both the ZmHK2 and ZmHK3 proteins of the present invention contain the conserved cytokinin-binding CHASE domain shown in Figure 1, further supporting their role in cytokinin sensing activity. Yonekura-Sakakibara et al. ((2004) Plant Physiol. 1 34: 1654-1661) demonstrated that similar ZmHK2 and ZmHK3 proteins are related to cytokinin sensory activity. The nucleotide and amino acid sequences of the proteins ZmHK2 (AB102956) and ZmHK3 (AB102957) used by Yonekura-Sakakibara et al. they are similar, but not identical, to the respective sequences ZmHK2 (SEQ ID N °: 4-6) and ZmHK3 (SEQ I D N °: 30-32) of the present invention. Example 3 METHODS OF USE OF THE POLYUCLEOTIDES OF THE INVENTION The polynucleotides of the invention can be used to alter the phenotype of plants. For example, the histidine kinase with cytokinin sensing activity of the present invention, when expressed under the direction of a promoter with preference for tissues in transgenic corn, will allow greater sensor activity of the available levels of cytokinin, which will lead to responses improved to cytokinin in certain tissues. The combination of the cytokinin sensing activity with a cytokinin biosynthesis gene (such as, sopentenyl transferase) in the expression, preferably by tissues in transgenic maize, will improve the responses to the greater amount of cytokinin produced. An increase in available cytokinin sensing activity could also be combined with a lower expression of a cytokinin degrading enzyme, such as a cytokinin oxidase, in certain tissues. If the cytokinin sensing activity is subsensible, the cytokinin responses can be reduced; This could be useful, for example, in roots, since cytokinins normally inhibit root growth. In addition, by introducing into a plant a polynucleotide of the invention comprising a functional histidine kinase coding sequence, histidine kinase can be overexpressed in the plant, thus inducing a typical response of the plant to environmental or hormonal stimuli in the absence of said stimuli. For example, overexpression of CKI 1 or CKI2 in Arabidopsis induces typical cytokinin responses, such as bud formation from of callus, cell proliferation and the like, in the absence of cytokinin in the medium (Kakimoto (1996) Science 274: 982-985). For example, female reproductive tissue and / or the photosynthesis apparatus can be selected for overexpression of a histidine kinase. In the first case, the greater perception of cytokinin could lead to a greater growth of the ears, and in the second one it could lead to a reduction or delay of the senescence. Still further, the polynucleotides of the invention, which comprise full-length or part-length histidine kinase coding sequences., can be used to subsensitize the expression of histidine kinases in a plant through the use of antisense and / or RNAi constructs. By subsensitizing histidine kinases in this way, the normal response of a plant to an environmental or hormonal stimulus can be inhibited. For example, the subsensitization of ZmCKI2 in roots by the use of a promoter with preference for roots can alter the normal responses of cytokinin in roots and consequently give rise to a greater root growth. In addition, the polynucleotides of the invention can be employed in methods for identifying other components of signal transduction cascades. In the trials of two yeast hybrids, the use of specific protein domains encoded by the polynucleotides of the invention will allow the identification of proteins interacting in vivo with the histidine kinases of the invention. These proteins that intervene in the interaction can be crucial to modify certain complex characteristics. In addition, these domains can be used as the starting point to construct protein interaction maps in the corresponding signal transduction pathways. This information will help in the identification of a protein or a gene in a path that should be the target to regulate a characteristic of interest in a plant.

EXAMPLE 4 Two-hybrid assays in yeast The two-hybrid yeast assays described in Example 1 were carried out in the following manner. Polyadenylated mRNA was isolated from aerial tissue of Arabidopsis using the set of elements for FastTrack ™ mRNA (Invitrogen, Carlsbad, CA, USA). A first strand of cDNA was created using a set of elements for cDNA synthesis (Stratagene, La Jolla, CA, USA), then cloned into pGADT7 (Clontech, Palo Alto, CA, USA) and then the cDNA library was transformed into yeast strain AH 109 (Clontech). The fragments of AtCKI2 were amplified by PCR, inserting the Sfil and BamHI sites at the 3 'and 5' ends, respectively, were cloned into a derivative of pGBKT7 (Clontech), pRSASKI 11, and sequenced. PRSASKI derivatives 1, which contain AT-CKI2 (5-367), pRM242; AT-CKI2 (357-922), pRM291; AT-CKI2 (5-205), pRM362; AT-CKI2 (200-367), pRM363; AT-CKI2 (357-61 5), pRM431; AT-CKI2 (590-922), pRM430, in Y187UH, a derivative of Y187 (Clontech) with the GAL4:: HIS reporter gene inserted in the ura locus and then self-reactivation of the HIS informant was evaluated. Y187UH, which contains the derivatives of pRSASKI ll, was paired with AH 109, which contains the cDNA library, and was allowed to grow on a synthetic medium that did not contain leucine, uracil, histidine and adenine. Plasmid DNA was isolated from the viable transformants using the set of elements for plasmids in yeast EZ (GenoTechnology, St. Louis, MO, USA) and the pGADT7 insert was amplified by PCR using vector-specific primers flanking the cloning site. The fragments of the PCR were sequenced and the vectors containing unique genes were transformed into Y187UH, with the respective pRSASKI derivative, to confirm histotin auxotrophy and activity? galactosidase AT-AHP coding sequences were inserted into the Sfil / BamHI sites of pGADT7 such as pRM751 (AHP1), pRM660 (AHP2), pRM661 (AHP3), pRM736 (AHP5). EXAMPLE 5 Transformation and regeneration of corn transgenic plants Immature maize embryos from greenhouse donor plants were bombarded with a plasmid containing a corn histidine kinase polynucleotide of the invention operably linked to a ubiquitin promoter and the marker gene selectable PAT (Wohlleben et al. (1988) Gene 70: 25-37), which confers resistance to the herbicide Bialaphos. If desired, the maize promoters, zag2.1 (NCBI GenBank Accession No. X80206) or ckxl (US Patent Publication No.:2002 / 52500) may be used in place of the ubiquitin promoter. Alternatively, the selection marker gene is provided in a separate plasmid. The transformation is carried out in the following manner. The contents of the media are described below. Preparation of the white tissue The ears are stripped and the surfaces were sterilized with 30% Clorox bleach plus 0.5% Micro detergent for 20 minutes and washed twice with sterile water. The immature embryos were trimmed and placed with the embryonic axis down (the scutellum upwards), at a rate of 25 embryos per plate, on medium 560Y for 4 hours and then aligned within the 2.5 cm white zone as preparation for the bombing. Preparation of DNA A plasmid vector comprising a histidine kinase polynucleotide of the invention is ligated operatively to a promoter of the invention. ubiquitin. This plasmid DNA and the plasmid DNA containing the PAT selectable marker were precipitated on 1.1 μm tungsten particles. (average diameter) using the following CaCl2 precipitation procedure: 100 μ? of tungsten particles prepared in water 10 μ? (1 pg) of DNA in Tris EDTA buffer (1 pg of total DNA) 100 μ? of CaC12 2.5 M 10 μ? of 0.1 M spermidine Each reagent was added successively to the suspension of tungsten particles, maintaining the vortexing on an agitator for multiple tubes. The final mixture was sonicated briefly and allowed to incubate under constant agitation for 10 minutes. After the precipitation period, the tubes were centrifuged briefly, the liquid was removed and the pellet was washed with 500 ml of 100% ethanol and centrifuged for 30 seconds. Again the liquid was removed and 105 μ? of 100% ethanol to the final pellet of tungsten particles. For bombardment with the particle gun, the tungsten / DNA particles were sonicated briefly and plated 10 μ? in the form of spots on the center of each macrocarrier and allowed to dry for approximately 2 minutes before the bombardment. Treatment with the particle gun The sample plates were bombarded at level No. 4 of the particle gun No. HE34-1 or No. HE34-2. All samples received a single shot at 650 psi, with a total of ten aliquots taken from each prepared particle / DNA tube.

Subsequent treatment After bombardment, the embryos were maintained on 560Y medium for 2 days, then transferred to 560R selection medium containing Bialaphos 3 mg / liter and subcultured every 2 weeks. After approximately 10 weeks of selection, the callus-resistant callus clones were transferred to medium 288J to initiate regeneration of the plant. After the maturation of the somatic embryos (2-4 weeks), these well-developed somatic embryos were transferred to a medium for germination and then taken to the culture room with light. Approximately 7-10 days later, the developing seedlings were transferred to hormone-free 272V medium in tubes for 7-10 days until the seedlings were well established. The plants were then transferred to inserts in boxes (equivalent to 2.5"pots) containing potting soil and cultivated for 1 week in the growth chamber, after another 1-2 weeks were grown in the greenhouse, then transferred to the classic 600 pots (1, 6 gallons) were grown to maturity.The plants were monitored and scored according to the increases or decreases in histidine kinase activity and / or levels of the histidine kinase protein. Cultivation The bombardment medium (560Y) comprises basal salts N6 4.0 g / l (SIGMA C-1416), mixture of vitamins Eriksson 1.0 ml / l (1000X SIGMA-151 1), thiamin HCI 0.5 mg / l, sucrose 120.0 g / l, 2,4-D 1, 0 mg / l and L-proline 2.88 g / l (brought to volume with H20 Dl after adjusting the pH to 5.8 with KOH); Gelhte 2.0 g / l (added after bringing to volume with H20 D-l); and silver nitrate 8.5 mg / l (added after sterilizing the medium and cooling to room temperature). The selection medium (560R) comprises N6 4.0 g / l basal salts (SIGMA C- 1416), mix of Eriksson's vitamins 1.0 ml / l (1000X SIGMA-1 51 1), thiamin HCI 0.5 mg / l, sucrose 30.0 g / l and 2,4-D 2.0 mg / l (brought to volume with H20 Dl after adjusting the pH to 5.8 with KOH); Geirite 3.0 g / l (added after bringing to volume with D-l H20); and silver nitrate 0.85 mg / l and Bialaphos 3.0 mg / l (both were added after sterilizing the medium and cooling to room temperature). The regeneration medium (288J) comprises MS salts 4.3 g / l (GIBCO 1 1 1 1 7-074), MS stock solution 5.0 ml / l (0, 100 g of nicotinic acid, thiamine HCl 0 , 02 g / l, pyridoxine HCl 0, 1 g / l and glycine 0.40 g / l brought to volume with polished H20 Dl) (Murashige and Skoog (1962) Physiol. Plant 1 5: 473), myo-inositol 100 mg / l, zeatin 0.5 mg / l, sucrose 60 g / l and abscisic acid 1.0 ml / l 0.1 mM (brought to volume with H 0 Dl polished after adjusting the pH to 5,6); 3.0 g / l Geirite (added after bringing to volume with H20 D-1); and indoleacetic acid 1.0 mg / l and Bialaphos 3.0 mg / l (added after sterilizing the medium and cooling to 60 ° C). The hormone-free medium (272V) comprises MS salts 4.3 g / l (GIBCO 1 1 1 1 7-074), MS stock solution 5.0 ml / l (nicotinic acid 0, 100 g / l, thiamin HCl 0.02 g / l, pyridoxine HCl 0, 10 g / l and glycine 0.40 g / l brought to volume with polished H20 Dl), myo-inositol 0.1 g / l and sucrose 40.0 g / l (taken to volume with polished H2O Dl after adjusting the pH in 5,6); and Bactoagar 6 g / l (added after bringing to volume with polished H20 D-l), sterilized and cooled to 60 ° C. Bombardment and culture medium The bombardment medium (560Y) comprises basal salts N6 4.0 g / l (SIGMA C-1416), Eriksson's mixture of 1.0 ml / l (1 000X SIGMA-51), thiamin HCl 0.5 mg / l, sucrose 120.0 g / l, 2,4-D 1.0 mg / l and L-proline 2.88 g / l (brought to volume with H20 Dl after adjusting the pH to 5 , 8 with KOH); Geirite 2.0 g / l (added after bringing to volume with H20 D-1); and 8.5 silver nitrate mg / l (added after sterilizing the medium and cooling to room temperature). The selection medium (560R) comprises basal salts N6 4.0 g / l (SIGMA C-1416), mixture of Eriksson vitamins 1.0 ml / l (1000X SIGMA-51 1), thiamin HCI 0.5 mg / l, sucrose 30.0 g / l and 2,4-D 2.0 mg / l (brought to volume with H20 Dl after adjusting the pH to 5.8 with KOH); Geirite 3.0 g / l (added after bringing to volume with D-l H20); and silver nitrate 0.85 mg / l and Bialaphos 3.0 mg / l (both were added after sterilizing the medium and cooling to room temperature). The regeneration medium (288J) comprises MS salts 4.3 g / l (GIBCO 1 1 1 1 7-074), MS stock solution 5.0 ml / l (0, 100 g of nicotinic acid, thiamine HCl 0 , 02 g / l, pyridoxine HCl 0, 10 g / l and glycine 0.40 g / l brought to volume with polished H20 Dl) (Murashige and Skoog (1962) Physiol. Plant 5: 473), myo-inositol 100 mg / l, zeatin 0.5 mg / l, sucrose 60 g / l and abscisic acid 1.0 ml / l 0.1 mM (brought to volume with polished H20 Dl after adjusting the pH to 5.6); 3.0 g / l Geirite (added after bringing to volume with H20 D-1); and indoleacetic acid 1.0 mg / l and Bialaphos 3.0 mg / l (added after sterilizing the medium and cooling to 60 ° C). The hormone-free medium (272V) comprises MS salts 4.3 g / l (GIBCO 1 1 1 1 7-074), MS stock solution 5.0 ml / l (nicotinic acid 0, 100 g / l, thiamin HCl 0.02 g / l, pyridoxine HCl 0.0 g / l and glycine 0.40 g / l brought to volume with polished H20 Dl), myo-inositol 0.1 g / l and sucrose 40.0 g / l (taken to volume with polished H2O Dl after adjusting the pH in 5,6); and Bactoagar 6 g / l (added after bringing to volume with polished H20 D-l), sterilized and cooled to 60 ° C.

EXAMPLE 6 Production of maize plants transformed by Agrobacterium-mediated transformation For the Agrobacterium-mediated transformation of maize with a corn histidine kinase polynucleotide of the invention, the Zhao method was preferably used (US Pat. 5,981,840, and PCT Patent Publication WO 98/32326, the contents of which are incorporated herein by reference). Briefly, immature maize embryos are isolated and the embryos are contacted with a suspension of Agrobacterium, where the bacteria have the ability to transfer the corn histidine kinase polynucleotide of the invention to at least one cell of at least one of the embryos. immature (step 1: the infection step). The embryos are co-cultivated for a time with Agrobacterium (step 2: the step of cocultivation). After this period of co-cultivation an optional step of "rest" is contemplated. In this resting step, the embryos are incubated in the presence of at least one antibiotic known to inhibit the growth of Agrobacterium without the addition of a selective agent for the plant transformants (step 3: resting step). Next, the inoculated embryos are cultured on medium containing a selection agent and the growing transformed calli are recovered (step 4: the selection step). The calluses are then regenerated in plants (step 5: the selection step). EXAMPLE 7 Transformation of soybean embryos and regeneration of transformed soybean plants Soybean embryos were bombarded with a plasmid containing a histidine kinase polynucleotide of the invention operatively linked to a constitutive promoter, such as the constitutive soybean promoter SCP1 (WO 97/47756, U.S. Patent No.: 6,555,673), to evaluate the functionality or a seed-specific promoter for a transgenic modification of the sensory activity of Cytokinin as follows. Alternatively, the corn, zag2.1 or ckx promoters can be used in place of the SCP1 promoter. In order to induce the formation of somatic embryos, cotyledons of 3-5 mm in length can be grown dissected from immature seeds, of sterilized surface, of the soybean cultivar A2872, with light or dark, at 26 ° C on a medium of appropriate agar for 6-10 weeks. Somatic embryos that produce secondary embryos are trimmed and placed in a suitable liquid medium. After a repeated selection of the somatic embryo groupings that multiplied as embryos in the early globular stage, the suspensions are maintained as described below. The embryogenic soy suspension cultures can be maintained in 35 ml of liquid medium on a rotary shaker, 1 50 rpm, at 26 ° C with fluorescent light, with a program of 16: 8 hours of day / night. The cultures are subcultured every two weeks by inoculating approximately 35 mg of tissue into 35 ml of liquid medium. The cultures can then be transformed into embryogenic soybean suspension by the particle gun bombardment method (Klein et al. (1987) Nature (London) 327: 70-73, US Patent No. 4,945,050 ). The DuPont Biolistic PDS 1000 / HE equipment (feedback with helium) can be used for these transformations. A selectable marker gene that can be used to facilitate transformation into soy is a transgene composed of the 35S promoter of the cauliflower mosaic virus (Odell et al. (1985) Nature 31 3: 810-812), the the hygromycin phosphotransferase of plasmid pJR225 (from E. coli; Gritz et al (1983) Gene 25: 179-188) and the 3 'region of the nopaline synthetase gene of the T-DNA of the Ti plasmid of Agrobacterium tumefaciens. The expression cassette of interest, comprising the histidine kinase polypeptide operably linked to the ubiquitin promoter, can be isolated as a restriction fragment. This fragment can then be inserted into a single restriction site in the vector carrying the marker gene. To 50 pl of a suspension 60 mg / ml of gold particles of 1 pm is added (in the order given): 5 μ? of DNA (1 pg / μ?), 20 pl of spermidine (0.1 M) and 50 μ? of CaC (2.5 M). The particle preparation is stirred for three minutes, passed through a microcentrifuge for 10 seconds and the supernatant is removed. The particles coated with DNA are then washed once in 400 μ? of ethanol 70% and resuspend in 40 μ? of anhydrous ethanol. The DNA / particle suspension can be sonicated three times for one second at a time. Then five pl of the gold particles coated with DNA are loaded onto each macrocarrier disk. Approximately 300-400 mg of a two-week suspension culture is placed in an empty 60 x 1.5 mm petri dish and the residual liquid is removed from the tissue with a pipette. For each transformation experiment, approximately 5-10 tissue plates are bombarded. The membrane rupture pressure is defined at 1 1 00 psi and the chamber is evacuated to a vacuum of 28 inches of mercury. The fabric is placed approximately 3.5 inches away from the retention screen and is bombarded three times. After the bombardment, the tissue can be divided in half, placed back into the liquid and cultured as described above.

Five to seven days after the bombardment, the liquid medium can be exchanged for fresh medium and eleven to twelve days after the bombardment by fresh medium containing 50 mg / ml hygromycin. This selective medium can be changed weekly. Seven to eight weeks after the bombardment, green transformed tissue can be seen growing from necrotic, non-transformed embryogenic clusters. The isolated green tissue is removed and inoculated in individual bottles in order to generate new embryogenic cultures transformed into suspension, propagated by cloning. Each new line can be treated as an independent transformation event. These suspensions can be subcultured and maintained as clusters of immature embryos or can be regenerated into whole plants by maturation and germination of the individual somatic embryos. EXAMPLE 8 Transformation of sunflower meristematic tissue and regeneration of transgenic sunflower plants Sunflower meristematic tissues were transformed with an expression cassette containing a histidine kinase polynucleotide of the invention operatively linked to a ubiquitin promoter in the following manner (see also European Patent No.: EP 0 486233, incorporated herein by reference, and Malone-Schoneberg et al. (1 994) Plant Science 103: 199-207). Mature seeds of sunflower (Helianthus annuus L.) were dehulled using a single-head sheller of wheat. Seed surfaces were sterilized for 30 minutes in a 20% Clorox bleach solution with the addition of two drops of Tween 20 per 50 ml of solution. The seeds were washed twice with sterile distilled water.

Split embryo axis explants were prepared using a modification of the procedures described by Schrammeijer et al. (Schrammeijer et al. (990) Plant Cell Rep. 9: 55-60). The seeds were imbibed in distilled water for 60 minutes after the surface sterilization process. Then the cotyledons of each seed are split, producing a clean fracture in the plane of the embryonic axis. After trimming the tip of the root, the explants were dissected longitudinally between the primordial leaves. The two halves are placed, with the surface cut up, on medium GBA consisting of mineral salts of Murashige and Skoog (Murashige et al. (1962) Physiol. Plant., 1 5: 473-497), Shepard's vitamin supplement (Shepard (1980) in Emergent Techniques for the Genetic Improvement of Crops (University of Minnesota Press, St. Paul, Minnesota), adenine sulfate 40 mg / l, sucrose 30 g / l, 6-benzyl aminopurine (BAP) 0.5 mg / l, indole-3-acetic acid (IAA) 0.25 mg / l, gibberellic acid (GA3) 0, 1 mg /, pH 5.6, and Phytagar 8 g / l. The explants were subjected to microprojectile bombardment before treatment with Agrobacterium (Bidney et al. (1992) Plant Mol. Biol. 18: 301-31 3). Thirty to forty explants are placed in a circle in the center of a 60 X 20 mm plate for this treatment. About 4.7 mg of 1.8 mm tungsten microprojectiles are resuspended in 25 ml of sterile TE buffer (1 mM Tris HCl, 1 mM EDTA, pH 8.0) and then 1.5 ml aliquots were used. by bombing. Each plate is bombarded twice through a 1 50 mm Nytex mesh located 2 cm above the samples in a PDS 1000® particle acceleration device. The disarmed EHA105 strain of Agrobacterium tumefaciens is used in all transformation experiments. A binary plasmid vector comprising the expression cassette containing the polynucleotide of histidine kinase operably linked to a constitutive promoter, such as the constitutive promoter of soybean SCP1 to evaluate the functionality or to a seed specific promoter for a transgenic modification of the cytokinin sensing activity. Alternatively, corn promoters can be used, zag2.1 or ckxl instead of the SCP1 promoter. The binary plasmid vector is introduced into the Agrobacterium strain EHA105 by freeze-thawing as described by Holsters et al. (1978) Mol. Gen. Genet. 163: 181-187. This plasmid further comprises a selectable marker gene of kanamycin (ie, nptll). Bacteria for plant transformation experiments are grown overnight (28 ° C and continuous agitation at 100 RPM) in liquid YEP medium (yeast extract 10 gm / l, Bactopeptone 10 gm / l and NaCl 5 gm / l, pH 7 , 0) with the appropriate antibiotics needed to maintain the bacterial strain and the binary plasmid. The suspension is used when it reaches an OD 600 between approximately 0.4 and 0.8. The Agrobacterium cells are pelleted and resuspended to a final DO600 of 0.5 in an inoculation medium composed of 12.5 mM MES pH 5.7; NH4CI 1 gm / l and MgSO4 0.3 gm / l. Freshly bombarded explants are placed in an Agrobacterium suspension, mixed and left to stand for 30 minutes. The explants are then transferred to GBA medium and co-cultivated, with the surface cut down, at 26 ° C and 18 hours light. After three days of co-culture, the explants are transferred to 374B medium (GBA medium containing no growth regulators and a reduced sucrose level of 1%) supplemented with cefotaxime 250 mg / l and kanamycin sulphate 50 mg / l. The explants are grown for two to five weeks on selection medium and then transferred to fresh 374B medium containing no kanamycin for one to two weeks of continuous development. Explants with areas of Growth in differentiation, resistant to antibiotics that have not produced adequate shoots for their excision are transferred to GBA medium containing cefotaxime 250 mg / l for a second 3-day treatment with phytohormones. Leaf samples from green shoots, resistant to kanamycin, are evaluated by the presence of NPTI I by an ELISA and by the presence of transgene expression by evaluating histidine kinase activity as described elsewhere herein. Positive outbreaks for NPTI I are grafted onto sunflower seedlings grown in vitro from Pioneer's 6440 hybrid. Seed sterilized seeds are germinated in medium 48-0 (Murashige and Skoog salts of intermediate strength, 0.5% sucrose, Gelrite 0.3%, pH 5.6) and are cultured under the conditions described for the culture of explants The upper portion of the seedling is removed, a vertical cut of 1 cm is made in the hypocotyl and the transformed shoot is inserted in the cut. The whole area is wrapped with waxed paper to ensure the outbreak. The grafted plants can be transferred to land after a week of in vitro culture. The grafts in are kept under conditions of high humidity followed by a slow adaptation to the environment of the greenhouse. The transformed sectors of Trj plants (parenteral generation) that are maturing in the greenhouse are identified by NPTI I ELISA and / or by an analysis of the histidine kinase activity in leaf extracts, while the transgenic seeds harvested from Trj plants positive for NPTI I are identified by an analysis of histidine kinase activity of small portions of dry seed cotyledon.

EXAMPLE 9 Transient expression of histidine kinase The plasmid comprising a histidine kinase polynucleotide of the invention operatively linked to a plant promoter is precipitated on gold particles with polyethyzimine (PEI, Sigma No. P3143), while the transgenic expression cassette ( UBI :: moPAT ~ GFPm :: pinll) to be integrated is precipitated on gold particles using the standard Ca ++ method. Briefly, the coating of the gold particles with PEI is carried out in the following manner. First the gold particles are washed. Thirty-five mg of gold particles are weighed and placed in a microcentrifuge tube, for example with an average diameter of 1.0 micron (ASI No. 162-0010) and then 1.2 ml of absolute EtOH are added and vortex for one minute. The tube is set aside for 15 minutes at room temperature and then centrifuged at high speed using a microcentrifuge for 15 minutes at 4 ° C. The supernatant is discarded and an aliquot of 1.2 ml of fresh EtOH is added, vortexed for one minute, centrifuged for one minute and the supernatant discarded again (this is repeated twice). An aliquot of 1.2 ml of fresh EtOH is added and this suspension (gold particles in EtOH) can be stored at -20 ° C per week. To coat the particles with polyethylinimine (PEI, Sigma No. P3143), start with 250 μl of washed gold particles / EtOH, centrifuge and discard the EtOH. Wash once in 100 μl H2Odd to remove residual ethanol. 250 μl of 0.25 mM PEI is added, pulsed to suspend the particles and then the tube is immersed in a dry ice / EtOH bath to instantly freeze the suspension. It is lyophilized during night. At this point, the coated, dried particles can be stored at -80 ° C for at least 3 weeks. Before use, the particles are washed 3 times with aliquots of 250 μ? of 2.5 mM HEPES buffer, pH 7, 1, with sonication by pulses 1 x and then a rapid vortex before each centrifugation. Is suspended in a final volume of 250 μ? of HEPES buffer solution. Aliquots of 25 μ? in new tubes before joining the DNA. To join the uncoated DNA, the particles are sonicated by pulses, then add the DNA and mix everything up and down the pipette several times. Allow to sit for at least 2 minutes, centrifuge briefly (for example for 10 seconds), remove the supernatant and add 60 μ? of EtOH. Small amounts are placed on macrocarriers and bombarded according to the standard protocol. For the precipitation of Ca ++ and the bombardment the standard protocol for PDS-1000 is used. The two particle preparations are mixed and the mixture is bombarded into plant cells (some cells only receive a particle with the polynucleotide of histidine kinase, while some cells only receive a particle PAT-GFP, and other cells receiving both). The PEI-mediated precipitation results in a high frequency of transient expression cells and extremely low frequencies of recovery of stable transformants (relative to the Ca ++ method). Therefore, the cassette containing the polynucleotide of histidine kinase precipitated PEI transiently expressed and stimulates a burst of activity of histidine kinase polynucleotide, but this plasmid does not integrate. The plasmid PAT-GFP released from Ca + 7 gold particles is integrated and expresses the seleccionare marker at a frequency that results in a substantially improved recovery of transgenic events. EXAMPLE 10 Transient expression of a polynucleotide and a histidine kinase polypeptide Transient expression of the histidine kinase polynucleotide product can be obtained by distributing polyadenylated RNA protected by the 5 'end of histidine kinase, expression cassettes containing histidine kinase DNA or a histidine kinase protein. All these molecules can be distributed using a biolistic particle gun. For example, polyadenylated RNA protected by the 5'-end of histidine kinase can be easily obtained in vitro using the mMessage mMachine® array of elements from Armbion (Austin, TX, USA). The RNA is co-distributed, using the procedure described above, together with DNA comprising a gene or gene fragment of agronomic interest and a marker for selection / screening, such as Ubi :: moPAT ~ GFPm:: pinl. The cells that receive the RNA can be validated as transgenic clonal colonies because they will also express the PAT-GFP fusion protein (and therefore will show green fluorescence under appropriate illumination). Plants regenerated from these embryos can then be examined for the presence of the gene of agronomic interest.

EXAMPLE 1 1 Histidine kinase variants Nucleotide sequence variants of SEQ ID N °: 1, 3, 4, 6, 7, 9, 1 3, 1 5, 16, 18, 26, 28, 30 and 32 that do not alter the encoded amino acid sequence The histidine kinase sequences shown in SEQ ID No. 1, 3, 4, 6, 7, 9, 13, 15, 16, 18, 26, 28, 30 and 32 are used to generate variants of nucleotide sequences that possess a nucleotide sequence for the open reading frame with 70% , 76%, 81%, 86%, 92% and 97% approximately of nucleotide sequence identity when compared to the nucleotide sequences of the unaltered initial ORFs of SEQ ID N °: 1, 3, 4, 6 , 7, 9, 13, 1 5, 16, 18, 26, 28, 30 and 32, respectively. These functional variants are generated using a standard codon table. As long as the nucleotide sequence of the variants is altered, the amino acid sequence encoded by the open reading frame does not change. B. Amino acid sequence variants of SEQ ID N °: 2, 8, 14, 1 7, 23 and 27 Variations of the amino acid sequences of histidine kinases are generated. In this example, an amino acid is altered. Specifically, the open reading frames shown in SEQ I D No. 2, 8, 14, 17, 23 or 27 are reviewed to determine the appropriate amino acid alteration. The selection of the amino acid to be changed is made by consulting the alignment of the protein (with the other orthologs and other members of the gene family of various species). See Figure 1. An amino acid is selected that is not considered under a high selection pressure (it is not highly conserved) and that can be replaced with relative ease by an amino acid of similar chemical characteristics (ie, similar functional side chains). The use of the alignment of The proteins shown in Figure 1 can be changed to the appropriate amino acid. Thus, variants that possess 70%, 75%, 81%, 86%, 92% and 97% approximately of nucleic acid sequence identity with SEQ ID N °: 2, 8, 14, 17, 23 or 27 are generated using this method. C. Additional variants of the amino acid sequences of the polypeptides of SEQ ID N °: 2, 8, 14, 17, 23 and 27 In this example, artificial protein sequences are created that present 82%, 87%, 92% and 97% identity in relation to the reference protein sequence. This last effort requires the identification of conserved and variable regions of the alignment shown in Figure 1 and then the prudent application of a table of amino acid substitutions. These parts will be described in more detail later. Mainly, the determination of which of the amino acid sequences are altered is made on the basis of the conserved regions between the histidine kinases proteins or between the other histidine kinase proteins. See Figure 1. Based on the sequence alignment, the different regions of the histidine kinase with probability of being altered are represented with lowercase letters, while the conserved regions are represented with capital letters. It is considered that conservative substitutions can be made in the regions conserved below without altering function. In addition, the skilled person will understand that the functional variants of the histidine kinase sequence of the invention may contain minor alterations of unconserved amino acids in the conserved domain. The conserved regions of the histidine kinases of hybrid type receptors are evident in Figure 1 and are described in the preceding brief description of Figure 1.

Then artificial protein sequences are created that are different from the original in the ranges of 80-85%, 85-90%, 90-95%, and 95-100% identity. The mean points of these intervals are searched, with a deviation of plus or minus 1%, for example. The amino acid substitutions will be made by the Perl commercial script. The table of substitutions is shown in Table 3 below. Table 3. Table of substitutions First, any amino acid conserved in the protein is identified that should not be changed and "marked" to isolate it from the substitution. The initial methionine will of course be added to this list automatically. Then the changes are made. H, C and P are not changed under any circumstances. The changes will take place with isoleucine first, going from N-terminal to C-terminal. Then the leucine, and so on, progressing through the list until the desired target is obtained. Interim substitutions can be made so as not to cause an inversion of the changes. The list is ordered from 1 -1 7, so you can start with as many changes of isoleucine as necessary before leucine and so on until you get to methionine. It is clear that in this way it will not be necessary to change many amino acids. L, I and V will comprise a 50: 50 substitution of the two alternative optimal substitutions. Variants of amino acid sequences are obtained in writing. Perl script is used to calculate the percentage identities. The use of this procedure allows the generation of histidine kinase variants that possess a 82%, 87%, 92% and 97% approximately of amino acid identity with respect to the initial unaltered amino acid sequences of SEQ ID N °: 2, 8, 14, 17, 23 or 27. The article "a" and "a", as used herein, refers to one or more than one (ie, at least one) of the grammatical objects that constitute the object of the article. By way of example, "an element" means one or more elements. All publications and patent applications mentioned in the specification are indicative of the level of those skilled in the art to which this invention is directed. All publications and patent applications are incorporated herein by reference as if each publication or individual patent application was specifically and individually incorporated herein by way of reference. Although the foregoing invention has been described in some detail by way of illustration and example in order to provide greater clarity for its understanding, it is clear that certain changes and modifications are possible within the scope of the appended claims. CITATIONS Aloni R, Langhans, Aloni E, Ullrich Cl (2004) Role of cytokinin in the regulation of root gravítropism. Plant 220: 177-182 Anantharaman V, Aravind L (2001) The CHASE domain: a predicted ligand-binding module in plant cytokinin receptors and other eukaryotic and bacterial receptors. Trends Biochem Sci 26: 579-582 Baulcombe DC, Saunders GR, Bevan MW, Mayo MA, Hanison MJ (1986) Expression of biologically-active viral satellite RNA from the nuclear genome of transformed plants. Nature 321: 446-449 Baxter-Burrell A, Chang R, Springer P, Bailey-Serres J (2003) Gene and enhancer trap transposable elements reveal oxygen deprivation-regulated genes and their complex patterns of expression in Arabidopsis. Ann Bot (Lond) 91 Spec No: 129-141 Bijlsma JJ, Groisman EA (2003) Making informed decisions: regulatory interactions between two-component systems. Trends Microbiol 1 1: 359-366 D'Agostino IB, Deruere J, Kieber JJ (2000) Characterization of the response of the Arabidopsis response regulator gene family to cytokinin. Plant Physiol 124: 1706-1717 Desikan R, A-H-Mackerness S, Hancock JT, Neill SJ (2001) Regulation of the Arabidopsis transcriptome by oxidative stress. Plant Physiol 127: 1 59-172 Gamble RL, Coonfield ML, Schaller GE (1998) Histidine kinase activity of the ETR1 ethylene receptor from Arabidopsis. Proc Nati Acad Sci U S 95: 7825-7829 Gilles-Gonzalez MA, González G (2004) Signal transduction by heme-containing PAS-domain proteins. J Appl Physiol 96: 774-783 Grefen C, Harter K (2004) Plant two-component systems: principles, functions, complexity and cross talk. Plant 219: 733-742 Hagen G, Guilfoyle T (2002) Auxin-responsive gene expression: genes, promoters and regulatory factors. Plant Mol Biol 49: 373-385 Higuchi, Pischke MS, Mahonen AP, Miyawaki K, Hashimoto Y, Seki M, Kobayashi M, Shinozaki K, Kato T, Tabata S, Helariutta Y, Sussmian MR, Kakimoto T (2004) In plant functions of the Arabidopsis cytokinin receptor family. Proc Nati Acad Sci U S A 101: 8821 -8826 Hirayama T, Oka A (1992) Novel protein kinase of Arabidopsis thaliana (APK1) that phosphorylates tyrosine, serine and threonine. Plant Mol Biol 20: 653-662 Hwang l, Chen HC, Sheen J (2002) Two-component signal transduction pathways in Arabidopsis. Plant Physiol 129: 500-515 Hwang I, Sheen J (2001) Two-component circuitry in Arabidopsis cytokinin signal transduction. Nature 413: 383-389 Inoue T, Higuchi M, Hashimoto Y, Seki M, Kobayashi M, Kato T, Tabata S, Shinozaki K, Kakimoto T (2001) Identification of CRE1 as a cytokinin receptor from Arabidopsis. Nature 409: 1060-1063 Ito T, Takahashi N, Shimura Y, Okada K (1997) A serine / threonine protein kinase gene isolated by an in vivo binding procedure using the Arabidopsis floral homeotic gene product, AGAMOUS. Plant Cell Physiol 38: 248-258 Kakimoto T (1996) CKI 1, a histidine kinase homolog implicated in cytokinin signal transduction. Science 274: 982-985 Kakimoto T (2002) Gene encoding protein participating in signal transduction of cytokinin. WO 2001/16332 Mougel C, Zhulin IB (2001) CHASE: an extracellular sensing domain common to transmembrane receptors from prokaryotes, lower eukaryotes and plants. Trends Biochem Sci 26: 582-584 Nakamura A, Kakimoto T, Imamura A, Suzuki T, Ueguchi C, Mizuno T (1999) Biochemical characterization of a putative cytokinin-responsive His-kinase, CKI 1, from Arabidopsis thaliana. Biosci Biotechnol Biochem 63: 1627-1630 Nishimura C, Ohashi Y, Sato S, Kato T, Tabata S, Ueguchi C (2004) Histidine kinase homologs that act as cytokinin receptors possess overlapping functions in the regulation of shoot and root growth n Arabidopsis. Plant Cell 16: 1 365-1 377 Rashotte AM, Carson SD, To JP, Kieber JJ (2003) Expression profiling of cytokinin action in Arabidopsis. Plant Physiol 132: 1 998-201 1 Schaller GE, Bleecker AB (1995) Ethylene-binding sites generated in yeast expressing the Arabidopsis ETR1 gene. Science 270: 809-1 81 1 Schaller GE, Mathews DE, Gribskov M, Walker JC (2002) Two-Component Signaling Elements and Histidyl-Aspartyl Phosphorelays. In CR Somerville, EM Meyerowitz, eds, The Arabidopsis Book. American Society of Plant Biologists Scheres B, Benfey P, Dolan L (2002) Root Development. In CR Somerville, EM Meyerowitz, eds, The Arabidopsis Book. American Society of Plant Biologists, Rockville, MD Stock AM, Robinson VL, Goudreau PN (2000) Two-component signal transduction. Annu Rev Biochem 69: 183-21 5 Taylor BL, Zhulin IB (1999) PAS domains: internal sensors of oxygen, redox potential, and light. Microbiol Mol Biol Rev 63: 479-506 Ueguchi C, Sato S, Kato T, Tabata S (2001) The AHK4 gene involved in the cytokinin-signaling pathway as a direct receptor molecule in Arabidopsis thaliana. Plant Cell Physiol 42: 751-755 Urao T, Miyata S, Yamaguchi-Shinozaki K, Shinozaki K (2000) Possible His to Asp phosphorelay signaling in an Arabidopsis two-component system. FEBS Lett 478: 227-232 Urao T, Yakubov B, Satoh R, Yamaguchi-Shinozaki K, Seki M, Hirayama T, Shinozaki K (1999) A transmembrane hybrid-type histidine kinase in Arabidopsis functions as an osmosensor. Plant Cell 1 1: 1 743-1 754 West AH, Stock AM (2001) Histidine kinases and response regulator proteins in two-component signaling systems. Trends Biochem Sci 26: 369-376 Yamada H, Suzuki T, Terada K, Takei K, Ishikawa K, Miwa K, Yamashino T, Mizuno T (2001) The Arabidopsis AHK4 histidine kinase sa cytokinin-binding receptor that transduces cytokinin signáis across the membrane Plant Cell Physiol 42: 1017-1023 Zhu J (2002) Salt and drought stress signal transduction in plants. Annu Rev Plant Biol 53: 247-273

Claims

CLAIMS: 1. An isolated polynucleotide, CHARACTERIZED BECAUSE comprises a nucleotide sequence selected from the group consisting of: (a) a nucleotide sequence comprising the SEQ ID N °: 1, 3, 4, 6, 7, 9, 13, 15, 16, 18, 26, 28, 30, 32; (b) a nucleotide sequence encoding an amino acid sequence comprising SEQ ID N °: 2, 5, 8, 14, 17, 27 or 31; (c) a nucleotide sequence that is 90% identical to SEQ ID NO:

1 . 3, 7, 9, 13, 15, 16, 18, 26 or 28; (d) a nucleotide sequence encoding a polypeptide comprising at least 50 consecutive amino acids of SEQ ID NOS: 2, 8, 14, 17 or 27, wherein said polypeptide retains histidine kinase activity; and (e) a nucleotide sequence that hybridizes under severe conditions with the complement of SEQ ID N °: 1, 3, 7, 9, 13, 15, 16, 18, 26 or 28, wherein said severe conditions comprise hybridization in 50% formamide, 1 M NaCI, 1% SDS at 37 ° C and at least one wash in 0.1 X SSC at a temperature between 60 ° C and 65 ° C.

2. A method for modulating the cytokinin response of a plant, CHARACTERIZED BY comprising transforming said plant with a recombinant expression cassette comprising a polynucleotide of clause 1 operatively linked to a promoter that directs expression in a plant.

3. The method of clause 2, CHARACTERIZED BECAUSE said promoter is a constitutive promoter.

4. The method of clause 2, CHARACTERIZED BECAUSE the promoter is a promoter with preference for tissues.

5. The method of clause 4, CHARACTERIZED BECAUSE the promoter directs expression in female reproductive tissue.

6. The method of clause 2, CHARACTERIZED BECAUSE the promoter is a promoter inducible by cytokinin. 7. The method of clause 2, CHARACTERIZED BECAUSE said modulation results in a greater sensitivity to cytokinin. 8. The method of clause 2, CHARACTERIZED BECAUSE this plant is a monocot. 9. An isolated polypeptide, CHARACTERIZED BECAUSE it comprises an amino acid sequence selected from the group consisting of: (a) an amino acid sequence comprising SEQ ID N °: 2, 5, 8, 14, 17, 23, 27 or 31; (b) an amino acid sequence comprising at least 70% sequence identity with SEQ ID NO: 2, 8, 14, 17, 23 or 27, wherein said polypeptide retains histidine kinase activity; (c) an amino acid sequence encoded by a nucleotide sequence that hybridizes under severe conditions with the complement of 1, 3,

7. 9, 13, 1 5, 16, 18, 26 or 28, where said severe conditions comprise hybridization in 50% formamide, 1 M NaCl, 1% SDS at 37 ° C, and at least one wash in 0.1 X SSC a a temperature between 60 ° C and 65 ° C; and, (d) an amino acid sequence comprising at least 50 consecutive amino acids of SEQ ID NO: 2, 8, 14, 17, 23 or 27, wherein said polypeptide retains the kinase activity. 10. A method for modulating the histidine kinase activity in a plant, CHARACTERIZED BECAUSE it comprises providing said plant with a polypeptide of clause 9. eleven . A transformed plant, CHARACTERIZED BECAUSE comprises a polynucleotide operatively linked to a promoter that directs expression in a plant, wherein said polynucleotide comprises a nucleotide sequence selected from the group consisting of: (a) a nucleotide sequence comprising SEQ ID No. : 1, 3, 4, 6, 7, 9, 13, 15, 16, 18, 26, 28, 30 or 32; (b) a nucleotide sequence encoding an amino acid sequence comprising SEQ ID N °: 2, 5, 8, 14, 17, 23, 27 or 31; (c) a nucleotide sequence comprising at least 70% sequence identity with SEQ ID NO: 1, 3, 7, 9, 13, 15, 16, 18, 26 or 28, wherein said polynucleotide encodes a polypeptide with histidine kinase activity; (d) a nucleotide sequence encoding an amino acid sequence comprising at least 70% sequence identity with SEQ ID N °: 2, 8, 14, 17 or 27, wherein said polynucleotide encodes a polypeptide comprising activity histidine kinase; (e) a nucleotide sequence that hybridizes under severe conditions with the complement of SEQ ID N °: 1, 3, 7, 9, 13, 15, 16, 18, 26 or 28, where said severe conditions comprise hybridization in 50% formamide, 1 M NaCl, 1% SDS at 37 ° C, and at least one wash in 0.1 X SSC at a temperature between 60 ° C and 65 ° C; and (f) a nucleotide sequence that is completely complementary to at least one sequence selected from the group consisting of the nucleotide sequences of (a) - (e). 12. The plant of clause 1, CHARACTERIZED BECAUSE said plant is a monocot. 1 3. The plant of clause 1 2, CHARACTERIZED BECAUSE said monocotyledons are corn, wheat, rice, barley, sorghum or rye. 14. The plant of clause 11, CHARACTERIZED BECAUSE said plant is a dicotyledonous plant. 1 5. The plant of clause 14, CHARACTERIZED BECAUSE the dicot is soy, Brassica, sunflower, cotton, Arabidopsis or alfalfa. 16. The plant of clause 11, CHARACTERIZED BECAUSE said polynucleotide is stably incorporated in the genome of the plant. 1 7. A transformed cell, CHARACTERIZED BECAUSE it is from the plant of clause 1 1. 1

8. A transformed seed, CHARACTERIZED BECAUSE it is from the plant of clause 1 1. 1

9. A method for modulating the level or activity of a polypeptide in a plant, CHARACTERIZED BECAUSE it comprises transforming said plant with a construct comprising a fragment of SEQ ID NO: 1, 3, 4, 6, 7, 9, 13 , 1 5, 16, 18, 26, 28, 30 or 32, or a fragment of the complement of any of them, where the expression of said fragment interrupts the transcription or translation of the corresponding endogenous polynucleotide or of an endogenous polynucleotide that is a 90 % identical to it 20. The method of clause 1 9, CHARACTERIZED BECAUSE said polypeptide is a histidine kinase. SUMMARY Isolated polynucleotides encoding histidine kinase polypeptides with cytokinin sensing activity, and the polypeptides encoded by them. Expression cassettes comprising the polynucleotides of the invention and plants and plant cells transformed with the polynucleotides are described. Also described are methods of using the polynucleotides and histidine kinase polypeptides with cytokinin sensing activity to modulate histidine kinase activity and / or histidine kinase levels in plants and plant cells.