WO2000018937A1 - Enzymes de glutathione-s-transferase issues du mais - Google Patents

Enzymes de glutathione-s-transferase issues du mais Download PDF

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Publication number
WO2000018937A1
WO2000018937A1 PCT/US1998/020502 US9820502W WO0018937A1 WO 2000018937 A1 WO2000018937 A1 WO 2000018937A1 US 9820502 W US9820502 W US 9820502W WO 0018937 A1 WO0018937 A1 WO 0018937A1
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seq
nucleic acid
host cell
gst enzyme
maize
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PCT/US1998/020502
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English (en)
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Brian Mcgonigle
Daniel P. O'keefe
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E.I. Du Pont De Nemours And Company
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Priority to AU10638/99A priority Critical patent/AU1063899A/en
Priority to EP98953210A priority patent/EP1117810A1/fr
Priority to CA002339349A priority patent/CA2339349A1/fr
Priority to PCT/US1998/020502 priority patent/WO2000018937A1/fr
Publication of WO2000018937A1 publication Critical patent/WO2000018937A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
    • C12N9/10—Transferases (2.)
    • C12N9/1085—Transferases (2.) transferring alkyl or aryl groups other than methyl groups (2.5)
    • C12N9/1088—Glutathione transferase (2.5.1.18)
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
    • C12N15/09—Recombinant DNA-technology
    • C12N15/63—Introduction of foreign genetic material using vectors; Vectors; Use of hosts therefor; Regulation of expression
    • C12N15/79—Vectors or expression systems specially adapted for eukaryotic hosts
    • C12N15/82—Vectors or expression systems specially adapted for eukaryotic hosts for plant cells, e.g. plant artificial chromosomes (PACs)
    • C12N15/8241—Phenotypically and genetically modified plants via recombinant DNA technology
    • C12N15/8261—Phenotypically and genetically modified plants via recombinant DNA technology with agronomic (input) traits, e.g. crop yield
    • C12N15/8271—Phenotypically and genetically modified plants via recombinant DNA technology with agronomic (input) traits, e.g. crop yield for stress resistance, e.g. heavy metal resistance
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
    • C12N15/09—Recombinant DNA-technology
    • C12N15/63—Introduction of foreign genetic material using vectors; Vectors; Use of hosts therefor; Regulation of expression
    • C12N15/79—Vectors or expression systems specially adapted for eukaryotic hosts
    • C12N15/82—Vectors or expression systems specially adapted for eukaryotic hosts for plant cells, e.g. plant artificial chromosomes (PACs)
    • C12N15/8241—Phenotypically and genetically modified plants via recombinant DNA technology
    • C12N15/8261—Phenotypically and genetically modified plants via recombinant DNA technology with agronomic (input) traits, e.g. crop yield
    • C12N15/8271—Phenotypically and genetically modified plants via recombinant DNA technology with agronomic (input) traits, e.g. crop yield for stress resistance, e.g. heavy metal resistance
    • C12N15/8274—Phenotypically and genetically modified plants via recombinant DNA technology with agronomic (input) traits, e.g. crop yield for stress resistance, e.g. heavy metal resistance for herbicide resistance

Definitions

  • This invention is in the field of plant molecular biology. More specifically, this invention pertains to nucleic acid fragments encoding maize glutathione-S-transferase (GST) enzymes involved in the detoxification of xenobiotic compounds in plants and seeds.
  • GST glutathione-S-transferase
  • Glutathione-S-transferases are a family of enzymes which catalyze the conjugation of glutathione, homoglutathione (hGSH) and other glutathione- like analogs via a sulfhydryl group, to a large range of hydrophobic, electrophilic compounds. The conjugation can result in detoxification of these compounds.
  • GST enzymes have been identified in a range of plants including maize (Wosnick et al., Gene (Amst) 16 (1) (1989) 153-160; Rossini et al., Plant Physiology (Rockville) 112 (4) (1996) 1595-1600; Holt et al., Planta (Heidelberg) 196 (2) (1995) 295-302), wheat (Edwards et al., Pestic. Biochem. Physiol. (1996) 54(2), 96-104), sorghum (Hatzios et al., J. Environ. Sci.
  • Glutathione S-transferases catalyze the nucleophilic attack of the thiol group of GSH to various electrophilic substrates.
  • GSTs Glutathione S-transferases
  • Their functions and regulation in plants has been recently reviewed (Marrs et al., Annu Rev Plant Physiol Plant Mol Biol 47:127-58 (1996); Droog, F. J Plant Growth Regul 16:95-107, (1997)). They are present at every stage of plant development from early embryogenesis to senescence and in every tissue class examined. The agents that have been shown to cause an increase in GST levels have the potential to cause oxidative destruction in plants, suggesting a role for GSTs in the protection from oxidative damage.
  • GSTs In addition to their role in the protection from oxidative damage, GSTs have the ability to nonenzymatically bind certain small molecules, such as auxin (Zettl et al. , PNAS 91 :689-693, (1994)) and perhaps regulate their bioavailability. Furthermore the addition of GSH to a molecule serves as an "address" to send that molecule to the plant vacuole (Marrs et al., Nature 375:397-400, (1995)). GSTs have also been implicated in the detoxification of certain herbicides. Maize GSTs have been well characterized in relation to herbicide metabolism. Three genes from maize have been cloned: GST 29 (Shah et al.
  • GST I a homodimer of GST 29
  • GST II a heterodimer of GST 29 and GST 27
  • GST III a homodimer of GST 26
  • GST IV a homodimer of GST 27
  • GST 27 is highly inducible by safener compounds (Jepson (1994) supra; Holt et al., Planta 196:295-302, (1995)) and overexpression of GST 27 in tobacco confers alachlor resistance to transgenic tobacco (Jepson, personal communication). Additionally, Bridges et al. (U.S. 5589614) disclose the sequence of a maize derived GST isoform II promoter useful for the expression of foreign genes in maize and wheat. In soybean, herbicide compounds conjugated to hGSH have been detected and correlated with herbicide selectivity (Frear et al., Physiol 20: 299-310 (1983); Brown et al. , Pest Biochem Physiol 29: 112-120, (1987)). This implies that hGSH conjugation is an important determinant in soybean herbicide selectivity although this hypothesis has not been characterized on a molecular level.
  • nucleic acid fragments encoding soybean GST to use in screening in assays, the creation of herbicide-tolerant transgenic plants, and altered production of GST enzymes depend on the heretofore unrealized isolation of nucleic acid fragments that encode all or a substantial portion of a soybean GST enzyme.
  • the present invention provides nucleic acid fragments isolated from maize encoding all or a substantial portion of a GST enzyme.
  • the isolated nucleic acid fragment is selected from the group consisting of (a) an isolated nucleic acid fragment encoding all or a substantial portion of the amino acid sequence selected from the group consisting of SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 18, SEQ ID NO:20, SEQ ID NO:22, and SEQ ID NO:24; (b) an isolated nucleic acid fragment that is substantially similar to an isolated nucleic acid fragment encoding all or a substantial portion of the amino acid sequence sequence selected from the group consisting of SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO:
  • the instant invention relates to chimeric genes encoding maize GST enzymes or to chimeric genes that comprise nucleic acid fragments as described above, the chimeric genes operably linked to suitable regulatory sequences, wherein expression of the chimeric genes results in altered levels of the encoded enzymes in transformed host cells.
  • the present invention further provides a transformed host cell comprising the above described chimeric gene.
  • the transformed host cells can be of eukaryotic or prokaryotic origin.
  • the ' invention also includes transformed plants that arise from transformed host cells of higher plants, and from seeds derived from such transformed plants, and subsequent progeny.
  • the invention provides methods of altering the level of expression of a maize GST enzyme in a host cell comprising the steps of; (i) transforming a host cell with the above described chimeric gene and; (ii) growing the transformed host cell produced in step (i) under conditions that are suitable for expression of the chimeric gene wherein expression of the chimeric gene results in production of altered levels of a plant GST enzyme in the transformed host cell relative to expression levels of an untransformed host cell.
  • the present invention provides methods of obtaining a nucleic acid fragment encoding all or substantially all of the amino acid sequence encoding a maize GST enzyme comprising either hybridization or primer-directed amplification methods known in the art and using the above described nucleic acid fragment.
  • a primer-amplification-based method uses SEQ ID NOS.: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, or 23. The product of these methods is also part of the invention.
  • Another embodiment of the invention includes a method for identifying a compound that inhibits the activity of a maize GST enzyme encoded by the nucleic acid fragment and substantially similar and complementary nucleic acid fragments of SEQ ID NOS.: 1-24.
  • the method has the steps: (a) transforming a host cell with the above described chimeric gene; (b) growing the transformed host cell under conditions that are suitable for expression of the chimeric gene wherein expression of the chimeric gene results in production of the GST enzyme; (c) optionally purifying the GST enzyme expressed by the transformed host cell; (d) contacting the GST enzyme with a chemical compound of interest; and
  • This method may further include conducting step (d) in the presence of at least one electrophilic substrate and at least one thiol donor.
  • the isolated nucleic acid fragments of this method are chosen from the group represented by SEQ ID NOS.: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23, and the maize GST enzyme is selected from the group consisting of SEQ ID NOS.: 2, 4, 6, 8,10, 12, 14, 16, 18, 20, 22, and 24.
  • the invention further provides a method for identifying a chemical compound that inhibits the activity of the maize GST enzyme as described herein, wherein the identification is based on a comparison of the phenotype of a plant transformed with the above described chimeric gene contacted with the inhibitor candidate with the phenotype of a transformed plant that is not contacted with the inhibitor candidate.
  • the isolated nucleic acid fragment of this method is selected from the group consisting of SEQ ID NOS.: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23 and the maize GST enzyme is selected from the group consisting of SEQ ID NOS.: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24.
  • the invention provides a method for identifying a substrate for the maize GST enzyme.
  • the method comprises the steps of: (a) transforming a host cell with a chimeric gene comprising the nucleic acid fragment as described herein, the chimeric gene encoding a maize GST enzyme operably linked to at least one suitable regulatory sequence; (b) growing the transformed host cell of step (a) under conditions that are suitable for expression of the chimeric gene resulting in production of the GST enzyme; (c) optionally purifying the GST enzyme expressed by the transformed host cell; (d) contacting the GST enzyme with a substrate candidate; and (e) comparing the activity of maize GST enzyme with the activity of maize GST enzyme that has been contacted with the substrate candidate and selecting substrate candidates that increase the activity of the maize GST enzyme relative to the activity of maize GST enzyme in the absence of the substrate candidate.
  • step (d) of this method is carried out in the presence of at least one thiol donor.
  • the isolated nucleic acid fragment of this method is selected from the group consisting of SEQ ID NOS.: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23, 25 and the maize GST enzyme is selected from the group consisting of SEQ ID NOS.: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24.
  • methods are provided for identifying a maize GST substrate candidate wherein the identification of the substrate candidate is based on a comparison of the phenotype of a host cell transformed with a chimeric gene expressing a maize GST enzyme and contacted with a substrate candidate with the phenotype of a similarly transformed host cell grown without contact with a substrate candidate.
  • the isolated nucleic acid fragment of this method is selected from the group consisting of SEQ ID NOS.: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23 and the maize GST enzyme is selected from the group consisting of SEQ ID NOS.: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24.
  • sequence descriptions and sequences listings attached hereto comply with the rules governing nucleotide and/or amino acid sequence disclosures in patent applications as set forth in 37 C.F.R. ⁇ 1.821-1.825.
  • the Sequence Descriptions contain the one letter code for nucleotide sequence characters and the three letter codes for amino acids as defined in conformity with the IUPAC-IYUB standards described in Nucleic Acids Research 75:3021-3030 (1985) and in the Biochemical Journal 219 (No. 2j:345-373 (1984) which are herein incorporated by reference.
  • SEQ ID NO: 1 is the nucleotide sequence comprising the cDNA insert in clone bmsl.pk0023.g8 encoding a maize GST.
  • SEQ ID NO:2 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone bmsl.pk0023.g8.
  • SEQ ID NO:3 is the nucleotide sequence comprising the cDNA insert in clone cs.pk0010.c5 encoding a maize GST.
  • SEQ ID NO:4 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone cs.pk0010.c5.
  • SEQ ID NO: 5 is the nucleotide sequence comprising the cDNA insert in clone cebl.pk0017.a5 encoding a maize GST.
  • SEQ ID NO:6 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone cebl.pk0017.a5.
  • SEQ ID NO: 7 is the nucleotide sequence comprising the cDNA insert in clone cc71se-a.pk0001.g2 encoding a maize class III GST.
  • SEQ ID NO:8 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone cc71se-a.pk0001.g2.
  • SEQ ID NO:9 is the nucleotide sequence comprising the cDNA insert in clone cc71se-b.pk0014.b8 encoding a maize class III GST.
  • SEQ ID NO: 10 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone cc71se-b.pk0014.b8.
  • SEQ ID NO:l 1 is the nucleotide sequence comprising the cDNA insert in clone ceb5.pk0051.f8 encoding a maize class III GST.
  • SEQ ID NO: 12 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone ceb5.pk0051.f8.
  • SEQ ID NO: 13 is the nucleotide sequence comprising the cDNA insert in clone crln.pk0003.bl encoding a maize class III GST.
  • SEQ ID NO: 14 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone crln.pk0003.bl.
  • SEQ ID NO: 15 is the nucleotide sequence comprising the cDNA insert in clone crln.pk0014.g8 encoding a maize class III GST.
  • SEQ ID NO: 16 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone crln.pk0014.g8.
  • SEQ ID NO: 17 is the nucleotide sequence comprising the cDNA insert in clone m.l5.5.d06.sk20 encoding a maize class II GST.
  • SEQ ID NO: 18 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone m.l5.5.d06.sk20.
  • SEQ ID NO: 19 is the nucleotide sequence comprising the cDNA insert in clone crln.pk0040.el2 encoding a maize class II GST.
  • SEQ ID NO:20 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone crln.pk0040.el2.
  • SEQ ID NO:21 is the nucleotide sequence comprising the cD A insert in clone ceb5.pk0049.al 1 encoding a maize class III GST.
  • SEQ ID NO:22 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone ceb5.pk0049.al 1.
  • SEQ ID NO:23 is the nucleotide sequence comprising the cDNA insert in clone csl.pk0059.e2 encoding a maize class III GST.
  • SEQ ID NO:24 is the deduced amino acid sequence of the nucleotide sequence comprising the cDNA insert in clone csl.pk0059.e2.
  • the transformed E. coli ceb5.pk0051.f8/pET30(LIC)BL21(DE3) containing the gene ceb5.pk0051.f8 in a pET30(LIC) vector encoding a maize class III GST was deposited on 21 August 1997 with the American Type Culture Collection (ATCC), 12301 Parklawn Drive, Rockville, MY 20852, U.S.A., under the terms of the Budapest Treaty on the International Recognition of the Deposit of Micro-organisms for the Purpose of Patent Procedure. The deposit is designated as ATCC 98511.
  • the present invention provides novel GST nucleotide sequences and encoded proteins isolated from maize.
  • GST enzymes are known to function in the process of detoxification of a variety of xenobiotic compounds in plants, most notably, herbicides.
  • Nucleic acid fragments encoding. at least a portion of several maize GST enzymes have been isolated and identified by comparison of random plant cDNA sequences to public databases containing nucleotide and protein sequences using the BLAST algorithms well known to those skilled in the art.
  • sequences of the present invention are useful in the construction of herbicide-tolerant transgenic plants, in the recombinant production of GST enzymes, in the development of screening assays to identify compounds inhibitory to the GST enzymes, and in screening assays to identify chemical substrates of the GSTs.
  • Glutathione S-Transferase or “GST” refers to any plant derived glutathione S-transferase (GST) enzyme capable of catalyzing the conjugation of glutathione, homoglutathione and other glutathione-like analogs via a sulfhydryl group, to hydrophobic and electrophilic compounds.
  • GST includes amino acid sequences longer or shorter than the length of natural GSTs, such as functional hybrid or partial fragments of GSTs, or their analogues.
  • GST is not intended to be delimited on the basis of enzyme activity but may encompass amino acid sequences that possess no measurable enzyme activity but are substantially similar in to those sequences, known in the art to possess the above mentioned glutathione conjugating activity.
  • class refers to a grouping of the various GST enzymes according to amino acid identity.
  • GST class I GST class II
  • GST class III GST class IV
  • the grouping of plant GSTs into three classes is described by Droog et al. (Plant Physiology 107:1139-1146 (1995)). All available amino acid sequences were aligned using the Wisconsin Genetics Computer Group package (Wisconsin Package Version 9.0, Genetics Computer Group (GCG), Madison, WI), and graphically represented on a phylogenetic tree.
  • class one including the archetypical sequences from maize GST I (X06755) and GST III (X04375); class two including the archetypical sequence from Dianthus caryophyllus (M64628); and class three including the archetypical sequence soybean GH2/4 (M20363).
  • class IV GSTs with its archetypical sequence being In2-1 (X58573).
  • an "isolated nucleic acid fragment” is a polymer of RNA or DNA that is single- or double-stranded, optionally containing synthetic, non- natural or altered nucleotide bases.
  • An isolated nucleic acid fragment in the form of a polymer of DNA may be comprised of one or more segments of cDNA, genomic DNA or synthetic DNA.
  • substantially similar refers to nucleic acid fragments wherein changes in one or more nucleotide bases results in substitution of one or more amino acids, but do not affect the functional properties of the protein encoded by the DNA sequence. “Substantially similar” also refers to nucleic acid fragments wherein changes in one or more nucleotide bases does not affect the ability of the nucleic acid fragment to mediate alteration of gene expression by antisense or co-suppression technology.
  • Substantially similar also refers to modifications of "the nucleic acid fragments of the instant invention such as deletion or insertion of one or more nucleotide bases that do not substantially affect the functional properties of the resulting transcript vis-a-vis the ability to mediate alteration of gene expression by antisense or co-suppression technology or alteration of the functional properties of the resulting protein molecule. It is therefore understood that the invention encompasses more than the specific exemplary sequences.
  • antisense suppression and co- suppression of gene expression may be accomplished using nucleic acid fragments representing less that the entire coding region of a gene, and by nucleic acid fragments that do not share 100% identity with the gene to be suppressed.
  • a codon for the amino acid alanine, a hydrophobic amino acid may be substituted by a codon encoding another less hydrophobic residue (such as glycine) or a more hydrophobic residue (such as valine, leucine, or isoleucine).
  • a codon encoding another less hydrophobic residue such as glycine
  • a more hydrophobic residue such as valine, leucine, or isoleucine
  • changes which result in substitution of one negatively charged residue for another such as aspartic acid for glutamic acid
  • one positively charged residue for another such as lysine for arginine
  • substantially similar sequences encompassed by this invention are also defined by their ability to hybridize, under stringent conditions (0.1X SSC, 0.1% SDS, 65 °C), with the sequences exemplified herein.
  • Preferred substantially similar nucleic acid fragments of the instant invention are those nucleic acid fragments whose DNA sequences are at least 80% identical to the DNA sequence of the nucleic acid fragments reported herein.
  • nucleic acid fragments are at least 90% identical to the identical to the DNA sequence of the nucleic acid fragments reported herein. Most preferred are nucleic acid fragments that are at least 95% identical to the DNA sequence of the nucleic acid fragments reported herein.
  • a "substantial portion" of an amino acid or nucleotide sequence comprising enough of the amino acid sequence of a polypeptide or the nucleotide sequence of a gene to putatively identify that polypeptide or gene, either by manual evaluation of the sequence by one skilled in the art, or by computer- automated sequence comparison and identification using algorithms such as BLAST (Basic Local Alignment Search Tool; Altschul, S. F., et al., (1993) J. Mol. Biol.
  • oligonucleotide probes comprising 20-30 contiguous nucleotides may be used in sequence-dependent methods of gene identification (e.g., Southern hybridization) and isolation (e.g., in situ hybridization of bacterial colonies or bacteriophage plaques).
  • short oligonucleotides of 12-15 bases may be used as amplification primers in PCR in order to obtain a particular nucleic acid fragment comprising the primers.
  • nucleotide sequence comprises enough of the sequence to specifically identify and/or isolate a nucleic acid fragment comprising the sequence.
  • the instant specification teaches partial or complete amino acid and nucleotide sequences encoding one or more particular fungal proteins. The skilled artisan, having the benefit of the sequences as reported herein, may now use all or a substantial portion of the disclosed sequences for purposes known to those skilled in this art. Accordingly, the instant invention comprises the complete sequences as reported in the accompanying Sequence Listing, as well as substantial portions of those sequences as defined above.
  • the term "complementary" is used to describe the relationship between nucleotide bases that are capable to hybridizing to one another.
  • adenosine is complementary to thymine and cytosine is complementary to guanine.
  • the instant invention also includes isolated nucleic acid fragments that are complementary to the complete sequences as reported in the accompanying Sequence Listing as well as those substantially similar nucleic acid sequences.
  • Codon degeneracy refers to divergence in the genetic code permitting variation of the nucleotide sequence without effecting the amino acid sequence of an encoded polypeptide. Accordingly, the instant invention relates to any nucleic acid fragment that encodes all or a substantial portion of the amino acid sequence encoding the GST enzymes as set forth in SEQ ID Nos: SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 18, SEQ ID NO:20, SEQ ID NO:22, and SEQ ID NO:24.
  • Synthetic genes can be assembled from oligonucleotide building blocks that are chemically synthesized using procedures known to those skilled in the art. These building blocks are ligated and annealed to form gene segments which are then enzymatically assembled to construct the entire gene.
  • “Chemically synthesized”, as related to a sequence of DNA means that the component nucleotides were assembled in vitro. Manual chemical synthesis ' of DNA may be accomplished using well established procedures, or automated chemical synthesis can be performed using one of a number of commercially available machines. Accordingly, the genes can be tailored for optimal gene expression based on optimization of nucleotide sequence to reflect the codon bias of the host cell. The skilled artisan appreciates the likelihood of successful gene expression if codon usage is biased towards those codons favored by the host. Determination of preferred codons can be based on a survey of genes derived from the host cell where sequence information is available.
  • Gene refers to a nucleic acid fragment that expresses a specific protein, including regulatory sequences preceding (5' non-coding sequences) and following (3' non-coding sequences) the coding sequence.
  • Native gene refers to a gene as found in nature with its own regulatory sequences.
  • Chimeric gene refers any gene that is not a native gene, comprising regulatory and coding sequences that are not found together in nature. Accordingly, a chimeric gene may comprise regulatory sequences and coding sequences that are derived from different sources, or regulatory sequences and coding sequences derived from the same source, but arranged in a manner different than that found in nature.
  • Endogenous gene refers to a native gene in its natural location in the genome of an organism.
  • a “foreign” gene refers to a gene not normally found in the host organism, but that is introduced into the host organism by gene transfer. Foreign genes can comprise native genes inserted into a non-native organism, or chimeric genes.
  • a “transgene” is a gene that has been introduced into the genome by a transformation procedure.
  • Coding sequence refers to a DNA sequence that codes for a specific amino acid sequence.
  • Suitable regulatory sequences refer to nucleotide sequences located upstream (5' non-coding sequences), within, or downstream (3' non-coding sequences) of a coding sequence, and which influence the transcription, RNA processing or stability, or translation of the associated coding sequence. Regulatory sequences may include promoters, translation leader sequences, introns, and polyadenylation recognition sequences.
  • Promoter refers to a DNA sequence capable of controlling the expression of a coding sequence or functional RNA.
  • a coding sequence is located 3' to a promoter sequence.
  • the promoter sequence consists of proximal and more distal upstream elements, the latter elements often referred to as enhancers.
  • an “enhancer” is a DNA sequence which can stimulate promoter activity and may be an innate element of the promoter or a heterologous element inserted to enhance the level or tissue-specificity of a promoter. Promoters may be derived in their entirety from a native gene, or be composed of different elements derived from different promoters found in nature, or even comprise synthetic DNA segments.
  • promoters may direct the expression of a gene in different tissues or cell types, or at different stages of development, or in response to different environmental conditions. Promoters which cause a gene to be expressed in most cell types at most times are commonly referred to as
  • the "translation leader sequence” refers to a DNA sequence located between the promoter sequence of a gene and the coding sequence.
  • the translation leader sequence is present in the fully processed mRNA upstream of the translation start sequence.
  • the translation leader sequence may affect processing of the primary transcript to mRNA, mRNA stability or translation efficiency. Examples of translation leader sequences have been described (Turner, R. and Foster, G.D. (1995) Molecular Biotechnology 3:225).
  • the "3' non-coding sequences” refer to DNA sequences located downstream of a coding sequence and include polyadenylation recognition sequences and other sequences encoding regulatory signals capable of affecting mRNA processing or gene expression.
  • the polyadenylation signal is usually characterized by affecting the addition of polyadenylic acid tracts to the 3' end of the mRNA precursor.
  • the use of different 3' non-coding sequences is exemplified by Ingelbrecht et al. ((1989) Plant Cell 7:671-680).
  • RNA transcript refers to the product resulting from RNA polymerase- catalyzed transcription of a DNA sequence. When the RNA transcript is a perfect complementary copy of the DNA sequence, it is referred to as the primary transcript or it may be a RNA sequence derived from posttranscriptional processing of the primary transcript and is referred to as the mature RNA.
  • Messenger RNA (mRNA) refers to the RNA that is without introns and that can be translated into protein by the cell.
  • cDNA refers to a double-stranded DNA that is complementary to and derived from mRNA.
  • Sense RNA transcript that includes the mRNA and so can be translated into protein by the cell.
  • Antisense RNA refers to a RNA transcript that is complementary to all or part of a target primary transcript or mRNA and that blocks the expression of a target gene (U.S. Pat. No. 5,107,065).
  • the complementarity of an antisense RNA may be with any part of the specific gene transcript, i.e., at the 5' non-coding sequence, 3' non-coding sequence, introns, or the coding sequence.
  • “Functional RNA” refers to antisense RNA, ribozyme RNA, or other RNA that is not translated yet has an effect on cellular processes.
  • operably linked refers to the association of nucleic acid sequences on a single nucleic acid fragment so that the function of one is affected by the other.
  • a promoter is operably linked with a coding sequence when it is capable of affecting the expression of that coding sequence (i.e., that the coding sequence is under the transcriptional control of the promoter).
  • Coding sequences can be operably linked to regulatory sequences in sense or antisense orientation.
  • expression refers to the transcription and stable accumulation of sense (mRNA) or antisense RNA derived from the nucleic acid fragment of the invention. Expression may also refer to translation of mRNA into a polypeptide.
  • Antisense inhibition refers to the production of antisense RNA transcripts capable of suppressing the expression of the target protein.
  • “Overexpression” refers to the production of a gene product in transgenic organisms that exceeds levels of production in normal or non-transformed organisms. “Co-suppression” refers to the production of sense RNA transcripts capable of suppressing the expression of identical or substantially similar foreign or endogenous genes (U.S. Pat. No. 5,231,020).
  • altered levels refers to the production of gene product(s) in transgenic organisms in amounts or proportions that differ from that of normal or non- transformed organisms.
  • “Mature” protein refers to a post-translationally processed polypeptide; i.e., one from which any pre- or propeptides present in the primary translation product have been removed.
  • Precursor protein refers to the primary product of translation of mRNA; i.e., with pre- and propeptides still present. Pre- and propeptides may be but are not limited to intracellular localization signals.
  • a "chloroplast transit peptide” is an amino acid sequence which is translated in conjunction with a protein and directs the protein to the chloroplast or other plastid types present in the cell in which the protein is made.
  • “Chloroplast transit sequence” refers to a nucleotide sequence that encodes a chloroplast transit peptide.
  • a “signal peptide” is an amino acid sequence which is translated in conjunction with a protein and directs the protein to the secretory system (Chrispeels, J.J., (1991) Ann. Rev. Plant Phys. Plant Mol. Biol. 42:21-53). If the protein is to be directed to a vacuole, a vacuolar targeting signal (supra) can further be added, or if to the endoplasmic reticulum, an endoplasmic reticulum retention signal (supra) may be added. If the protein is to be directed to the nucleus, any signal peptide present should be removed and instead a nuclear localization signal included (Raikhel (1992) Plant Phys.100:1621-1632).
  • Transformation refers to the transfer of a nucleic acid fragment into the genome of a host organism, resulting in genetically stable inheritance. Host organisms containing the transformed nucleic acid fragments are referred to as “transgenic” organisms. Examples of methods of plant transformation include Agrobacterium-mediated transformation (De Blaere et al. (1987) Meth. Enzymol. 143:211) and particle-accelerated or “gene gun” transformation technology (Klein et al. (1987) Nature (London) 327:10-13; U.S. Pat. No. 4,945,050).
  • the term "herbicide-tolerant plant” as used herein is defined as a plant that survives and preferably grows normally at a usually effective dose of a herbicide. Herbicide tolerance in plants according to the present invention refers to detoxification mechanisms in a plant, although the herbicide binding or target site is still sensitive.
  • Thiol donor refers to a compound that contains the structure RSH (where
  • suitable thiol donors may include, but are not limited to, Glutathione and homoglutathione.
  • Electrophilic substrate refers to a compound that is amenable to conjugation with glutathione or homoglutathione via a sulfhydryl group. Electrophilic substrates include a wide variety of compounds including pesticides, anti-pathogenic compounds such as fungicides and profungicides, pheramones, and herbicides. Within the context of the present invention electrophilic substrates with herbicidal activity may include, but are not limited to, chlorimuronethyl, alachlor, and atrazine, l-chloro-2,4-dinitrobenzene (CDNB), ethacrynic acid, t-stilbene oxide, and l,2-epoxy-3-(p-nitrophenoxy)propane.
  • CDNB l-chloro-2,4-dinitrobenzene
  • Thiol donor refers to a compound that contains the structure RSH (where R is not equal to H).
  • suitable thiol donors may include, but are not limited to, Glutathione and homoglutathione.
  • Electrophilic substrate refers to a compound that is amenable to conjugation with glutathione or homoglutathione via a sulfhydryl group. Electrophilic substrates include a wide variety of compounds including pesticides, anti-pathogenic compounds such as fungicides and profungicides, pheramones, and herbicides.
  • electrophilic substrates with herbicidal activity may include, but are not limited to, chlorimuronethyl, alachlor, and atrazine, l-chloro-2,4-dinitrobenzene (CDNB), ethacrynic acid, t-stilbene oxide, and l,2-epoxy-3-(p-nitrophenoxy)propane.
  • CDNB l-chloro-2,4-dinitrobenzene
  • ethacrynic acid ethacrynic acid
  • t-stilbene oxide t-stilbene oxide
  • l,2-epoxy-3-(p-nitrophenoxy)propane l,2-epoxy-3-(p-nitrophenoxy)propane.
  • the nucleic acid fragments of the instant invention may be used to isolate cDNAs and genes encoding homologous enzymes from the same or other plant species. Isolation of homologous genes using sequence-dependent protocols is well known in the art. Examples of sequence-dependent protocols include, but are not limited to, methods of nucleic acid hybridization, and methods of DNA and RNA amplification as exemplified by various uses of nucleic acid amplification technologies (e.g., polymerase chain reaction, ligase chain reaction).
  • genes encoding other GST enzymes could be isolated directly by using all or a portion of the instant nucleic acid fragments as DNA hybridization probes to screen libraries from any desired plant using methodology well known to those skilled in the art.
  • Specific oligonucleotide probes based upon the instant nucleic acid sequences can be designed and synthesized by methods known in the art (Maniatis).
  • the entire sequences can be used directly to synthesize DNA probes by methods known to the skilled artisan such as random primers DNA labeling, nick translation, or end-labeling techniques, or RNA probes using available in vitro transcription systems.
  • primers can be designed and used to amplify a part of or full-length of the instant sequences.
  • the resulting amplification products can be labeled directly during amplification reactions or labeled after amplification reactions, and used as probes to isolate full length cDNA or genomic fragments under conditions of appropriate stringency.
  • two short segments of the instant nucleic acid fragments may be used in polymerase chain reaction protocols to amplify longer nucleic acid fragments encoding homologous genes from DNA or RNA.
  • the polymerase chain reaction may also be performed on a library of cloned nucleic acid fragments wherein the sequence of one primer is derived from the instant nucleic acid fragments, and the sequence of the other primer takes advantage of the presence of the polyadenylic acid tracts to the 3' end of the mRNA precursor encoding plant genes.
  • the second primer sequence may be based upon sequences derived from the cloning vector.
  • the skilled artisan can follow the RACE protocol (Frohman et al., (1988) PNAS USA 55:8998) to generate cDNAs by using PCR to amplify copies of the region between a single point in the transcript and the 3' or 5' end.
  • Primers oriented in the 3' and 5' directions can be designed from the instant sequences.
  • 3' RACE or 5' RACE systems BBL
  • specific 3' or 5' cDNA fragments can be isolated (Ohara et al., (1989) PNAS USA 86:5613; Loh et al., (1989) Science 243:217).
  • Products generated by the 3' and 5' RACE procedures can be combined to generate full-length cDNAs (Frohman, M.A. and Martin, G.R., (1989) Techniques 7:165).
  • Synthetic peptides representing portions of the instant amino acid sequences may be synthesized. These peptides can be used to immunize animals to produce polyclonal or monoclonal antibodies with specificity for peptides or proteins comprising the amino acid sequences. These antibodies can be then be used to screen cDNA expression libraries to isolate full-length cDNA clones of interest (Lerner, R.A. (1984) Adv. Immunol. 36: 1 ; Maniatis).
  • nucleic acid fragments of the instant invention may be used to create transgenic plants in which the disclosed GST enzymes are present at higher or lower levels than normal or in cell types or developmental stages in which they are not normally found: This would have the effect of altering the level of GST enzyme available as well as the herbicide tolerant-phenotype of the plant.
  • Overexpression of the GST enzymes of the instant invention may be accomplished by first constructing chimeric genes in which the coding region are operably linked to promoters capable of directing expression of a gene in the desired tissues at the desired stage of development.
  • the chimeric genes may comprise promoter sequences and translation leader sequences derived from the same genes. 3' Non-coding sequences encoding transcription termination signals must also be provided.
  • the instant chimeric genes may also comprise one or more introns in order to facilitate gene expression.
  • any combination of any promoter and any terminator capable of inducing expression of a GST coding region may be used in the chimeric genetic sequence.
  • Some suitable examples of promoters and terminators include those from nopaline synthase (nos), octopine synthase (ocs) and cauliflower mosaic virus (CaMV) genes.
  • One type of efficient plant promoter that may be used is a high level plant promoter.
  • Such promoters, in operable linkage with the genetic sequence for GST, should be capable of promoting expression of the GST such that the transformed plant is tolerant to an herbicide due to the presence of, or increased levels of, GST enzymatic activity.
  • High level plant promoters that may be used in this invention include the promoter of the small subunit (ss) of the ribulose-1 ,5- bisphosphate carboxylase from example from soybean (Berry-Lowe et al., J. Molecular andApp. Gen., 1:483-498 1982)), and the promoter of the chlorophyll a/b binding protein. These two promoters are known to be light- induced in plant cells (See, for example, Genetic Engineering of Plants, an Agricultural Perspective, A. Cashmore, Plenum, New York (1983), pages 29-38; Coruzzi, G. et al., 77ze Journal of Biological Chemistry, 258:1399 (1983), and Dunsmuir, P. et al., Journal of Molecular and Applied Genetics, 2:285 (1983)).
  • Plasmid vectors comprising the instant chimeric genes can then constructed.
  • the choice of plasmid vector depends upon the method that will be used to transform host plants. The skilled artisan is well aware of the genetic elements that must be present on the plasmid vector in order to successfully transform, select and propagate host cells containing the chimeric gene. The skilled artisan will also recognize that different independent transformation events will result in different levels and patterns of expression (Jones et al., (1985) EMBOJ. 4:2411-2418; De Almeida et al., (1989) Mol. Gen. Genetics 275:78-86), and thus that multiple events must be screened in order to obtain lines displaying the desired expression level and pattern.
  • Such screening may be accomplished by Southern analysis of DNA blots (Southern, J. Mol. Biol. 98, 503, (1975)). Northern analysis of mRNA expression (Kroczek, J. Chromatogr. Biomed. Appl, 618 (1-2) (1993) 133-145), Western analysis of protein expression, or phenotypic analysis.
  • the chimeric genes described above may be further supplemented by altering the coding sequences to encode enzymes with appropriate intracellular targeting sequences such as transit sequences (Keegstra, K., Cell 55:247-253 (1989)), signal sequences or sequences encoding endoplasmic reticulum localization (Chrispeels, J.J., Ann. Rev. Plant Phys. Plant Mol. Biol. 42:2 -53 (1991)), or nuclear localization signals (Raikhel, N.
  • chimeric genes designed for co-suppression of the instant GST enzymes can be constructed by linking the genes or gene fragments encoding the enzymes to plant promoter sequences.
  • chimeric genes designed to express antisense RNA for all or part of the instant nucleic acid fragments can be constructed by linking the genes or gene fragment in reverse orientation to plant ⁇ promoter sequences.
  • Either the co-suppression or antisense chimeric genes could be introduced into plants via transformation wherein expression of the corresponding endogenous genes are reduced or eliminated.
  • Plants transformed with the present GST genes will have a variety of phenotypes corresponding to the various properties conveyed by the GST class of proteins. Glutathione conjugation catalyzed by GSTs is known to result in sequestration and detoxification of a number of herbicides and other xenobiotics (Marrs et al., Annu. Rev. Plant Physiol. Plant Mol. Biol. 47:127-58 (1996)) and thus will be expected to produce transgenic plants with this phenotype.
  • GST proteins are known to be induced by various environmental stresses such as salt stress (Roxas, et al, Stress tolerance in transgenic seedlings that overexpress glutathione S-transferase. Annual Meeting of the American Society of Plant Physiologists, (March 1997), abstract 1574, Final Program, Plant Biology and Supplement to Plant Physiology, 301), exposure to ozone (Sharma et al., Plant Physiology, 105 (4) (1994) 1089-1096), and exposure to industrial pollutants such as sulfur dioxide (Navari-Izzo et al., Plant Science 96 (1-2) (1994) 31-40). It is contemplated that transgenic plants, tolerant to a wide variety of stresses, may be produced by the present method by expressing foreign GST genes in suitable plant hosts.
  • the instant GST enzymes produced in heterologous host cells can be used to prepare antibodies to the enzymes by methods well known to those skilled in the art.
  • the antibodies are useful for detecting the enzymes in situ in cells or in vitro in cell extracts.
  • Preferred heterologous host cells for production of the instant GST enzymes are microbial hosts. Microbial expression systems and expression vectors containing regulatory sequences that direct high level expression of foreign proteins are well known to those skilled in the art. Any of these could be used to construct chimeric genes for production of the instant GST enzymes. These chimeric genes could then be introduced into appropriate microorganisms via transformation to provide high level expression of the enzymes.
  • Vectors or cassettes useful for the transformation of suitable host cells are well known in the art.
  • the vector or cassette contains sequences directing transcription and translation of the relevant gene, a selectable marker, and sequences allowing autonomous replication or chromosomal integration.
  • Suitable vectors comprise a region 5' of the gene which harbors transcriptional initiation controls and a region 3 ' of the DNA fragment which controls transcriptional termination. It is most preferred when both control regions are derived from genes homologous to the transformed host cell, although it is to be understood that such control regions need not be derived from the genes native to the specific species chosen as a production host.
  • Initiation control regions or promoters which are useful to drive expression of the genes encoding the GST enzymes in the desired host cell are numerous and familiar to those skilled in the art. Virtually any promoter capable of driving these genes is suitable for the present invention including but not limited to CYC1, HIS3, GAL1, GAL10, ADH1, PGK, PHO5, GAPDH, ADC1, TRPl, URA3, LEU2, ENO, TPI (useful for expression in Saccharomyces); AOX1 (useful for expression in Pichid); and lac, trp, ⁇ P L , ⁇ P ⁇ , T7, tac, and trc (useful for expression in E. coli).
  • Termination control regions may also be derived from various genes native to the preferred hosts. Optionally, a termination site may be unnecessary, however, it is most preferred if included.
  • Example 5 An example of a vector for high level expression of the instant GST enzymes in a bacterial host is provided (Example 5).
  • the instant maize GST enzymes can be used as a targets to facilitate design and/or identification of inhibitors of the enzymes that may be useful as herbicides or herbicide synergists. This is desirable because the enzymes described herein catalyze the sulfhydryl conjugation of glutathione to compounds toxic to the plant. Conjugation can result in detoxification of these compounds. It is likely that inhibition of the detoxification process will result in inhibition of plant growth or plant death. Thus, the instant maize GST enzymes could be appropriate for new herbicide or ' herbicide synergist discovery and design.
  • nucleic acid fragments of the instant invention may also be used as probes for genetically and physically mapping the genes that they are a part of, and as markers for traits linked to expression of the instant enzymes. Such information may be useful in plant breeding in order to develop lines with desired phenotypes or in the identification of mutants.
  • the instant nucleic acid fragments may be used as restriction fragment length polymorphism (RFLP) markers.
  • Southern blots Mantonis
  • Mantonis Maniatis
  • the resulting banding patterns may then be subjected to genetic analyses using computer programs such as MapMaker
  • nucleic acid fragments of the instant invention may be used to probe Southern blots containing restriction endonuclease-treated genomic DNAs of a set of individuals representing parent and progeny of a defined genetic cross. Segregation of the DNA polymorphisms is noted and used to calculate the position of the instant nucleic acid sequence in the genetic map previously obtained using this population (Botstein et al., (1980) Am. J. Hum. Genet. 52:314-331).
  • nucleic acid probes derived from the instant nucleic acid sequences may also be used for physical mapping (i.e., placement of sequences on physical maps; see Hoheisel et al., In: Nonmammalian Genomic Analysis: A Practical Guide, Academic press 1996, pp. 319-346, and references cited therein).
  • nucleic acid probes derived from the instant nucleic acid sequences may be used in direct fluorescence in situ hybridization (FISH) mapping.
  • FISH fluorescence in situ hybridization
  • nucleic acid amplification-based methods of genetic and physical mapping may be carried out using the instant nucleic acid sequences. Examples include allele-specific amplification, polymorphism of PCR-amplified fragments (CAPS), allele-specific ligation, nucleotide extension reactions, Radiation Hybrid Mapping and Happy Mapping.
  • the sequence of a nucleic acid fragment is used to design and produce primer pairs for use in the amplification reaction or in primer extension reactions. The design of such primers is well known to those skilled in the art.
  • EXAMPLE 1 Composition of cDNA Libraries; Isolation and Sequencing of cDNA Clones cDNA libraries representing mRNAs from various maize tissues were prepared. The characteristics of the libraries are described in Table 1.
  • cDNA libraries were prepared in Uni-ZAPTM XR vectors according to the manufacturer's protocol (Stratagene Cloning Systems, La Jolla, CA). The Uni-ZAPTM XR libraries were converted into plasmid libraries according to the protocol provided by Stratagene. Upon conversion, cDNA inserts were contained in the plasmid vector pBluescript. cDNA inserts from randomly picked bacterial colonies containing recombinant pBluescript plasmids were amplified via polymerase chain reaction using primers specific for vector sequences flanking the inserted cDNA sequences. Amplified insert DNAs were sequenced in dye-primer sequencing reactions to generate partial cDNA sequences (expressed sequence tags or "ESTs"; see Adams, M. D. et al., (1991) Science 252:1651). The resulting ESTs were analyzed using, a Perkin Elmer Model 377 fluorescent sequencer.
  • BLAST Basic Local Alignment Search Tool; Altschul, S. F., et al., (1993) J. Mol. Biol. 215:403-410; see also www.ncbi.nlm.nih.gov/BLAST/) searches for similarity to sequences contained in the BLAST "nr" database (comprising all non-redundant GenBank CDS translations, sequences derived from the 3-dimensional structure Brookhaven Protein Data Bank, SWISS-PROT protein sequence database, EMBL, and DDBJ databases).
  • GenBank CDS GenBank CDS translations
  • sequences derived from the 3-dimensional structure Brookhaven Protein Data Bank SWISS-PROT protein sequence database
  • EMBL EMBL
  • DDBJ databases DDBJ databases
  • Example 5 describes the sequencing strategy for the above described clones.
  • a chimeric gene comprising a cDNA encoding a maize GST enzyme in sense orientation can be constructed by polymerase chain reaction (PCR) of the cDNA clone using appropriate oligonucleotide primers. Cloning sites (Ncol or Smal) can be incorporated into the oligonucleotides to provide proper orientation
  • Amplification is then performed in a 100 ⁇ L volume in a standard PCR mix consisting of 0.4 mM of each oligonucleotide and 0.3 pM of target DNA in 10 mM Tris-HCl, pH 8.3, 50 mM KC1, 1.5 mM MgCl 2 , 200 mM dGTP, 200 mM dATP, 200 mM dTTP, 200 mM dCTP and 0.025 unit DNA polymerase.
  • Reactions are carried out in a Perkin-Elmer Cetus ThermocyclerTM for 30 cycles comprising 1 min at 95 °C, 2 min at 55 °C and 3 min at 72 °C, with a final 7 min extension at 72 °C after the last cycle.
  • the amplified DNA is then digested with restriction enzymes Ncol and Smal and fractionated on a 0.7% low melting point agarose gel in 40 mM Tris-acetate, pH 8.5, 1 mM EDTA.
  • the appropriate band 0 can be excised from the gel, melted at 68 °C and combined with a 4.9 kb Ncol-Smal fragment of the plasmid pML103.
  • Plasmid pML103 has been deposited under the terms of the Budapest Treaty at ATCC (American Type Culture Collection, 12301 Parklawn Drive, Rockville, MD 20852), and bears accession number ATCC 97366.
  • the DNA segment from pML103 contains a 1.05 kb Sall-Ncol promoter fragment of the maize 27 kD zein gene and a 0.96 kb Smal-Sall fragment from the 3' end of the maize 10 kD zein gene in the vector pGem9Zf(+) (Promega Corp 7113 Benhart Dr, Raleigh, NC).
  • Vector and insert DNA can be ligated at 15 °C overnight, essentially as described (Maniatis). The ligated DNA may then be used to transform E.
  • Bacterial transformants can be screened by restriction enzyme digestion of plasmid DNA and limited nucleotide sequence analysis using the dideoxy chain termination method DNA Sequencing Kit; U. S. Biochemical).
  • the resulting plasmid construct would comprise a chimeric gene encoding, in the 5' to 3* direction, the maize 27 kD zein promoter, a cDNA fragment encoding a plant GST enzyme, and the 10 kD zein 3' region.
  • the chimeric gene described above can then be introduced into corn cells by the following procedure.
  • Immature corn embryos can be dissected from developing caryopses derived from crosses of the inbred corn lines H99 and LH132 (Indiana Agric. ⁇ xp. Station, Indiana, USA). The embryos are isolated 10 to 11 days after pollination when they are 1.0 to 1.5 mm long. The embryos are then placed with the axis-side facing down and in contact with agarose-solidified N6 medium (Chu et al., (1975) Sci. Sin. Peking 18:659-668). The embryos are kept in the dark at 27 °C.
  • Friable embryogenic callus consisting of undifferentiated masses of cells with somatic proembryoids and embryoids borne on suspensor structures proliferates from the scutellum of these immature embryos.
  • the embryogenic callus isolated from the primary explant can be cultured on N6 medium and sub-cultured on this medium every 2 to 3 weeks.
  • the plasmid, p35S/Ac obtained from Dr. Peter ⁇ ckes, Hoechst Ag, v Frankfurt, Germany
  • This plasmid contains the Pat gene (see European Patent Publication 0 242 236) which encodes phosphinothricin acetyl transferase (PAT).
  • the enzyme PAT confers resistance to herbicidal glutamine synthetase inhibitors such as phosphinothricin.
  • the pat gene in p35S/Ac is under the control of the 35S promoter from Cauliflower Mosaic Virus (Odell et al. (1985) Nature 313:810-812) and the 3M region of the nopaline synthase gene from the T-DNA of the Ti plasmid of Agrobacterium tumefaciens.
  • the particle bombardment method (Klein et al., (1987) Nature 327:70-73) may be used to transfer genes to the callus culture cells. According to this method, gold particles ((1 ⁇ m in diameter) are coated with DNA using the following technique.
  • plasmid DNAs are added to 50 uL of a suspension of gold particles (60 mg per mL).
  • Calcium chloride 50 ⁇ L of a 2.5 M solution
  • spermidine free base 20 ⁇ L of a 1.0 M solution
  • the suspension is vortexed during the addition of these solutions.
  • the tubes are briefly centrifuged (5 sec at 15,000 rpm) and the supernatant removed.
  • the particles are resuspended in 200 ⁇ L of absolute ethanol, centrifuged again and the supernatant removed.
  • the ethanol rinse is performed again and the particles resuspended in a final volume of 30 uL of ethanol.
  • An aliquot (5 ⁇ L) of the DNA-coated gold particles can be placed in the center of a flying disc (Bio-Rad Labs, 861 Ridgeview Dr, Medina, OH).
  • the particles are then accelerated into the corn tissue with a PDS-1000/He (Bio-Rad Labs, 861 Ridgeview Dr, Medina, OH), using a helium pressure of 1000 psi, a gap distance of 0.5 cm and a flying distance of 1.0 cm.
  • the embryogenic tissue is placed on filter paper over agarose- solidified N6 medium. The tissue is arranged as a thin lawn and covered a circular area of about 5 cm in diameter.
  • the petri dish containing the tissue can be placed in the chamber of the PDS-1000/He approximately 8 cm from the stopping screen.
  • the air in the chamber is then evacuated to a vacuum of 28 inches of Hg.
  • the macrocarrier is accelerated with a helium shock wave using a rupture membrane that bursts when the He pressure in the shock tube reaches 1000 psi.
  • Seven days after bombardment the tissue can be transferred to N6 medium that contains gluphosinate (2 mg per liter) and lacks casein or proline. The tissue continues to grow slowly on this medium. After an additional 2 weeks the tissue can be transferred to fresh N6 medium containing gluphosinate.
  • Plants can be regenerated from the transgenic callus by first transferring clusters of tissue to N6 medium supplemented with 0.2 mg per liter of 2,4-D. After two weeks the tissue can be transferred to regeneration medium (Fromm et al., (1990) Bio/Technology 8:833-839).
  • EXAMPLE 4 Expression of Chimeric Genes in Tobacco Cells (Dicotyledon ' ) Cloning sites (Xbal or Smal) can be incorporated into the oligonucleotides to provide proper orientation of the DNA fragment when inserted into the digested vector pBI121 (Clonetech Inc., 6500 Donlon Rd, Somis, CA) or other appropriate transformation vector. Amplification could be performed as described above and the amplified DNA would then be digested with restriction enzymes Xbal and Smal and fractionated on a 0.7% low melting point agarose gel in 40 mM Tris- acetate, pH 8.5, 1 mM EDTA.
  • the appropriate band can be excised from the gel, melted at 68 °C and combined with a 13 kb Xbal-Smal fragment of the plasmid pBI121 and handled as in Example 3.
  • the resulting plasmid construct would comprise a chimeric gene encoding, in the 5' to 3' direction, right border region, the nos promoter linked to the NPT II gene and a nos terminator region followed by a cauliflower mosaic virus 35S promoter linked to a cDN ' A fragment encoding a plant GST enzyme and the nos terminator 3' region flanked by the left border region.
  • the resulting plasmid could be mobilized into the ⁇ gr ⁇ bacterium strain BA4404/pAL4404 (Hoekema et al.
  • EXAMPLE 5 Expression Of Chimeric Genes In Microbial Cells And Purification Of Gene Product Example 5 illustrates the expression of isolated full length genes encoding either class I, II or III GST proteins in E. coli.
  • LIC ligation independent cloning
  • the vector was then used to transform BL21(DE3) competent E. coli hosts.
  • Primers with a specific 3' extension designed for ligation independent cloning were designed to amplify the GST gene (Maniatis). Amplification products were gel-purified and annealed into the LIC vector after treatment with T4 DNA polymerase (Novagen). Insert-containing vectors were then used to transform NovaBlue competent E. coli cells and transformants were screened for the presence of viable inserts. Clones in the correct orientation with respect to the T7 promoter were transformed into BL21(D ⁇ 3) competent cells (Novagen) and selected on LB agar plates containing 50 ⁇ g/mL kanamycin.
  • Expressed protein was purified using the HIS binding kit (Novagen) according to the manufacturer ' s instructions. Purified protein was examined on 15-20% SDS Phast Gels (Bio-Rad Laboratories, 861 Ridgeview Dr, Medina, OH) and quantitated spectrophotometrically using BSA as a standard. Protein data is tabulated below in Table 3.
  • the GST enzymes expressed and purified as described in Example 5 were screened for their ability to metabolize a variety of substrates. Substrates tested included the three herbicide electrophilic substrates chlorimuron ethyl, alachlor, and Atrazine, and four model electrophilic substrates, l-chloro-2, 4-dinitro- benzene (CDNB), ethacrynic acid, t-stilbene oxide, and l,2-epoxy-3-(p-nitro- phenoxy) propane. The enzymes were purified as described in Example 5 and used in the following assay.
  • the conjugation reaction with each electrophilic substrate was performed by incubating 0.3 to 30 ⁇ g enzyme in 0.1 M MOPS (pH 7.0) containing 0.4 mM of the electrophilic substrate.
  • the reaction was inititated by the addition of glutathione to a final concentration of 4 mM. After 5 to 30 min, the reaction was terminated by the addition of 45 ⁇ L acetonitrile, micro fuged for 10 min to remove precipitated protein, and then the supernatent was removed and added to 65 ⁇ l of water.
  • the gradient started with 5% solvent B. progressing from 5% to 75% solvent B between 1 and 10 min. and from 75% to 95% solvent B between 10 and 12 min. Control reactions without enzyme were performed to correct for uncatalyzed reaction. Quantitation of metabolites were based on an assumption that the extinction coefficient of the conjugate was identical to that of the electrophilic substrate.
  • Table 4 shows the activity of each enzyme measured in with the seven different substrates. Activities are related to the activities of the

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Abstract

Cette invention concerne des fragments d'acides nucléiques isolés codant la totalité ou une grande partie des enzymes de glutathione-S-transférase (GST) qui sont issues du maïs et qui jouent un rôle dans la détoxification de composés xénobiotiques dans les plantes et les graines. Cette invention concerne également la construction de gènes chimériques qui codent la totalité ou une grande partie des enzymes de GST issues du maïs, des cellules hôtes transformées à l'aide de ces gènes ainsi que des procédés de production recombinante d'enzymes de GST issues du maïs. Cette invention concerne en outre des procédés de construction de plantes transgéniques possédant des niveaux modifiés d'enzymes de GST, ainsi que des cribles permettant d'identifier des substrats d'enzymes de GST issues du maïs et des inhibiteurs d'enzymes de GST issues du maïs.
PCT/US1998/020502 1998-09-30 1998-09-30 Enzymes de glutathione-s-transferase issues du mais WO2000018937A1 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
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WO2000047747A2 (fr) * 1999-02-10 2000-08-17 E.I. Du Pont De Nemours And Company Glutathion-s-transferases du mais
WO2004048577A1 (fr) * 2002-11-22 2004-06-10 Biovitrum Ab Utilisation d'inhibiteurs de la gst a3-3 et de la gst a1-1 pour le traitement du cancer

Citations (2)

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WO2004048577A1 (fr) * 2002-11-22 2004-06-10 Biovitrum Ab Utilisation d'inhibiteurs de la gst a3-3 et de la gst a1-1 pour le traitement du cancer

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