WO2001066779A2 - L'arabitol ou le ribitol, marqueurs par selection positive - Google Patents

L'arabitol ou le ribitol, marqueurs par selection positive Download PDF

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WO2001066779A2
WO2001066779A2 PCT/US2001/007474 US0107474W WO0166779A2 WO 2001066779 A2 WO2001066779 A2 WO 2001066779A2 US 0107474 W US0107474 W US 0107474W WO 0166779 A2 WO0166779 A2 WO 0166779A2
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cells
nucleotide sequence
gene
transformed
seq
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PCT/US2001/007474
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WO2001066779A3 (fr
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Wayne Parrott
Peter Lafayette
Patrick Kane
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Univ. Of Georgia Research Foundation, Inc.
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Priority to AU2001240117A priority Critical patent/AU2001240117A1/en
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Publication of WO2001066779A3 publication Critical patent/WO2001066779A3/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
    • C12N9/0004—Oxidoreductases (1.)
    • C12N9/0006—Oxidoreductases (1.) acting on CH-OH groups as donors (1.1)
    • 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
    • C12N15/11—DNA or RNA fragments; Modified forms thereof; Non-coding nucleic acids having a biological activity
    • C12N15/52—Genes encoding for enzymes or proenzymes
    • 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)
    • C12N15/8201—Methods for introducing genetic material into plant cells, e.g. DNA, RNA, stable or transient incorporation, tissue culture methods adapted for transformation
    • C12N15/8209—Selection, visualisation of transformants, reporter constructs, e.g. antibiotic resistance markers
    • 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)
    • C12N15/8201—Methods for introducing genetic material into plant cells, e.g. DNA, RNA, stable or transient incorporation, tissue culture methods adapted for transformation
    • C12N15/8209—Selection, visualisation of transformants, reporter constructs, e.g. antibiotic resistance markers
    • C12N15/821—Non-antibiotic resistance markers, e.g. morphogenetic, metabolic markers

Definitions

  • transformation is generally understood in the biotech and chemical arts to refer to a stable incorporation of a foreign DNA or RNA into a cell which results in a permanent, heritable alteration in the cell. It is well known that when new genetic material is to be introduced into a population of cells by transformation, only a certain number of the cells are successfully transformed. It is then necessary to identify the genetically transformed cells so that these cells can be separated from the non- transformed cells of the population. Identification and separation of the transformed cells has traditionally been accomplished using "negative selection", whereby the transformed cells are able to survive and grow, while the non-transformed cells are subjected to growth inhibition or perhaps even killed by a substance which the transformed cells, by virtue of their transformation, are able to tolerate.
  • selection of the transformed cells typically takes place using a selection gene which codes for antibiotic or herbicide resistance.
  • the selection gene hich in itself generally has no useful function in the transformed plant (and may in fact be undesirable in the plant) is coupled to or co-introduced with the desired gene to be incorporated into the plant, so that both genes are incorporated into the population of cells, or rather into certain of the cells in the population, since it is difficult, if not impossible, in practice to transform all of the cells.
  • the cells are then cultivated on or in a medium containing the antibiotic or herbicide to which the genetically transformed cells are resistant by virtue of the selection gene, thereby allowing the transformed cells to be identified, since the non- transformed cells-which do not contain the antibiotic or herbicide resistance gene in question— are subjected to growth inhibition or are killed.
  • the non-transformed cells may die because of the presence of antibiotics or herbicides in the growth medium.
  • the population of cells is a coherent tissue there is a risk that not only the non-transformed cells but also the transformed cells may die, due to the fact that the death of the non-transformed cells may cut off the supply of nutrients to the transformed cells or because the damaged or dying non- transformed cells may excrete toxic compounds.
  • Another disadvantage of negative selection is that the presence of an unnecessary gene, for example antibiotic resistance, may be undesirable.
  • antibiotic resistance may be undesirable.
  • Positive selection is a selection system whose operating principle is converse to negative selection. Rather than conferring resistance to a negative or toxic substance, positive selection involves conferring onto the transformed cell a metabolic, or other, competitive advantage over nontransformed cells. Positive selection systems identify and select genetically transformed cells without damaging or killing the nontransformed cells in the population and without co-introduction of antibiotic or herbicide resistance genes. As alluded to above, there is increasing concern that genes conferring resistance to antibiotics and/or herbicides may disperse and be incorporated into agriculturally destructive weeds and other plants, as well as pathogenic bacteria. Indeed, transgenic plants have been banned in the European Union. As a result, more and more investigative efforts are being made to develop positive selection systems for use in plants and other cell types.
  • the subject invention relates to a positive selection system that involves conferring to transferred cells the ability to metabolize arabitol, ribitol, and/or mannitol.
  • One aspect of the subject invention pertains to a gene construct comprising a gene of interest and a selectable marker gene.
  • a specific aspect pertains to supplying to a population of cells at least one marker compound which is directly or indirectly active in the transformed cells containing the gene of interest and is inactive or less active in the non-transformed cells whereby the transformed cells are provided with a selective advantage.
  • the selective advantage is one wherein the expression of the gene of interest or the positive selecting gene leads to an increase in the activity of an enzyme found endogenously in the population of cells such that the activity of the enzyme in the transformed cells is greater than the activity of the enzyme in non- transformed cells.
  • the marker compound supplied to the population of cells is selected from the group consisting of arabitol, ribitol, mannitol or a derivative or variant thereof.
  • a further aspect pertains to transformed cells selected according to the above- recited method. Moreover, an additional aspect pertains to plants derived from said transformed cells.
  • the invention includes both positive selection and negative selection including the use of a gene coding for antibiotic or herbicide resistance.
  • Yet a further aspect of the invention relates to genetically transformed cells comprising a gene of interest and selectable marker gene wherein the selectable marker gene induces a positive effect in the transformed cells and gives said cells a selective advantage when a population of cells including the transformed cells and nontransformed cells is supplied with a compound.
  • another aspect of the invention includes a method of selecting genetically transformed cells from a population of cells comprising a) introducing into the genome of a cell a gene of interest and a selectable marker gene; b) obtaining transformed cells; c) supplying to the population of cells a marker compound wherein said transformed cells have a selective advantage over non-transformed cells due to expression or transcription of the gene of interest or the selectable marker gene in the presence of the marker compound; and d) selecting said transformed cells from the population of cells wherein said selectable marker gene comprises a ribitol or D-arabitol dehydrogenase, a ribitol or D- arabitol kinase, a ribitol or D-arabitol transporter gene, or a combination thereof, and the compound is arabitol, ribitol or a derivative precursor thereof.
  • an additional aspect of the subject invention pertains to polynucleotide molecules that encode proteins having the biological activity of ribitol or arabitol dehydrogenase, ribitol or arabitol kinase, ribitol or arabitol transporter, or ribitol or arabitol repressor.
  • the aspect pertains to a polynucleotide as shown in SEQ ID NOS: 1 and 2, or functional fragments and variants thereof.
  • another aspect of the subject invention pertains to a polypeptide encoded by the polynucleotide molecules of the subject invention.
  • a further aspect of the subject invention pertains to cells transformed with the polynucleotide molecules of the subject invention.
  • transformed bacteria fungi, yeast, animal and plant cells. More specifically exemplified are transformed bacteria and plant cells.
  • Figure 1 shows a schematic of the isolation and cloning of the E. coli rtl operon.
  • the final position denotes if the plasmid had an insert cloned into its multiple cloning site: a '-' means no insert, and G refers to a GUS construct.
  • SEQ ID NO:l represents the nucleotide sequence of the arabitol dehydrogenase gene from E. coli strain C.
  • SEQ ID NO: 2 represents a polynucleotide molecule which comprises a nucleotide sequence encoding the rtl operon from E. coli strain C.
  • Bases 96 to 848 encode for ribitol dehydrogenase.
  • Bases 859 to 2463 encode for ribitol kinase.
  • Bases 2565 to 3839 encode for ribitol transporter.
  • SEQ ID NO: 3 represents the amino acid sequence of E. coli strain C ribitol dehydrogenase.
  • SEQ ID NO: 4 represents the amino acid sequence of E. coli strain C ribitol kinase.
  • SEQ ID NO: 5 represents the amino acid sequence of E. coli strain C ribitol transporter.
  • gene of interest refers to any nucleotide sequence, which is to be incorporated into the cells to produce genetically transformed cells.
  • Introduction of nucleotide sequence into plants, microorganisms and animals is widely practiced, and there are no limitations upon the nucleotide sequences whose presence may be detected by use of the positive selection method described herein.
  • the presence of the gene of interest in the genetically transformed cells may be determined without the above-mentioned disadvantages associated with traditional negative selection systems.
  • selectable marker gene refers to any nucleotide sequence that is preferably co-introduced with a gene of interest, wherein a selective advantage is conferred to a cell transformed with said selectable marker gene.
  • the gene of interest is directed to one or more functional genes that are chosen to provide a new plant trait, to enhance an existing plant trait, or to otherwise modify expression of plant phenotypes exhibited by the plant.
  • Such traits include herbicide resistance, pesticide resistance, disease resistance, enviromnental tolerance (e.g., heat, cold, drought, salinity), morphology, growth characteristics, nutritional content, taste yield, horticultural characteristics, consumer (quality) traits, and the like.
  • a functional gene to be introduced may be a structural gene which encodes a polypeptide which imparts the desired phenotype.
  • the functional gene may be a regulatory gene which might play a role in transcnptional and/or translational control to suppress, enhance, or otherwise modify the transcription and/or expression of an endogenuous gene within the plant. It will be appreciated that control of gene expression can have a direct impact on the observable plant characteristics.
  • sense and anti-sense constructs referred to above often have all or a portion of the transcript of the native gene operably linked to a promoter sequence at the 5' end of the transcribable segment, and operably linked to the 3" sequence of another gene (including polyadenylation sequences) at the 3' end of the transcribable segment.
  • the promoter sequence could be one of the many plant active sequences already described.
  • other plant-active promoter sequences could be derived specifically to be linked to the transcribable segment.
  • the promoter can be endogenous to a particular plant species, or can be from an exogenous source such as a cauliflower mosaic virus 35S promoter (Odell et al., Nature 313:810-812 (1985)), the ubiquitin 1 promoter, or the Smas promoter.
  • the 3' end sequence to be added can be derived from another plant gene, or less preferably from any other eukaryotic gene.
  • a gene of interest is co-introduced with a selectable marker gene refers to the fact that the sequences are coupled to each other or otherwise introduced together in such a manner that the presence of the selectable marker gene in a cell indicates that the gene of interest has been introduced into the cell.
  • the two nucleotide sequences are typically, although not necessarily, part of the same genetic construct and are introduced by the same vector.
  • a genetic construct containing the two nucleotides sequences will typically, but not necessarily, contain regulatory sequences enabling expression of each nucleotide sequence for example, promoter and transcription temiinators.
  • cells within the context of the present invention is intended to refer to any type of cells from which individual genetically transformed cells may be identified and isolated using the method of the invention, and includes cells of plants, animals and microorganisms such as bacteria, fungi, yeast, etc. Furthermore, the term cell is includes protoplasts. Particularly preferred cells are plant cells and bacteria.
  • transformed plant cells and plants, seeds or progeny derived therefrom include: fruits such as tomato, mango, peach, apple, pear, strawberry, banana and melon; field crops such as canola, sunflower, tobacco, soybean and sugar beet; small grain cereals such as wheat, barley, rice, corn, and cotton; ornamentals; forages such as alfalfa, clover, forage grasses; forest trees; and vegetables crops such as potato, carrot, lettuce, cabbage and onion. Most preferably are soybean and corn.
  • the term "population of cells” refers to any group of cells which has be subjected to genetic transformation.
  • the population may be a tissue, an organ or a portion thereof, a population of individual cells in or on a substrate, for example, a culture of microorganism cells, or a whole organism, for example, an entire plant.
  • selecting refers to the process of identifying and/or isolating genetically transformed cells from the non-transformed cells in a population of cells using the methods disclosed herein.
  • the gene of interest and the selectable marker gene may be introduced independently.
  • the same bacteria may be used for incorporation of both genes and incorporating a relatively large number of copies of the gene of interest into the cells, whereby the probability is relatively high that cells which are shown to express the selectable marker gene also will contain and express the gene of interest.
  • Independent introduction of two or more genes resulting in co-expression of the genes in the same cell is generally expected to have low probability, and the improved selection frequencies obtained by the positive selection method described herein are therefore expected to be especially advantageous in such systems.
  • marker compound may be any compound or nutrient in inactive or precursor form wliich in the absence of, for example, expression of the selectable marker gene exists in a form which is substantially biologically inactive with respect to the cells in question, but which when the selectable marker gene is expressed or transcribed is hydrolyzed or otherwise activated or metabolized so as to provide the genetically transformed cells containing the gene of interest with a selective advantage, and thereby allowing the cells to be selected.
  • Preferred compounds include, but are not limited to, arabitol or ribitol and derivatives or precursors thereof, and alternatively mannitol and derivatives and precursors thereof.
  • a “derivative" of arabitol or ribitol refers to any compounds capable of being utilized by, binding to, being a substrate for, or a product of any protein involved, either directly or indirectly, in the metabolism of arabitol or ribitol.
  • the marker compound used in the invention need not be one which is activated directly by a polypeptide encoded by the selectable marker gene. It may be activated indirectly, for example whereby the selectable marker gene has an indirect effect upon the marker compound in genetically transformed cells but not in non-transformed cells.
  • the selectable marker gene may be one which upon expression in the transformed cells, for example, indirectly increases the activity of an enzyme which is endogenous to the population of cells, thereby leading to a greater enzyme activity and activation of the compound in question in the genetically transformed cells.
  • selective advantage includes the terms selective, metabolic and physiological advantage and means that the transformed cells are able to grow more quickly than disadvantaged (non-transformed) cells, or are advantageously able to utilize substrates (such as nutrient precursors, etc.) which disadvantaged cells are not able to utilize, or are able to detoxify substrates which are toxic or otherwise growth inhibitory to disadvantaged cells or a combination thereof.
  • substrates such as nutrient precursors, etc.
  • the non- transformed cells do not necessarily suffer any severe disadvantage in the sense of being damaged or killed or as is the case with negative selection using antibiotics or herbicides.
  • the positive selection as used in the context of the present invention refers to the use of a selectable marker gene which produces or increases a positive effect of an added compound on the transformed cells.
  • a protein which is "involved in the metabolism of a marker compound” is typically, but not exclusively, an enzyme which may be responsible directly or indirectly for the production or utilization of the marker compound or its derivatives or precursors.
  • the protein may also be involved in the metabolism of a marker compound if it binds to it, transfers it from one site to another within or transport into the cell or tissue or organism or otherwise sequesters it thereby altering its local availability.
  • a region of nucleotide sequence which "regulates the activity of a gene encoding a protein” may alter the level of expression of an endogenous gene by being a .promoter, or having a promoter activity therefor, and by being introduced in or near its vicinity. By “near” is meant up to 10,000 kb.
  • indirect regulation may arise by altering the binding of RNA polymerase to the promoter of a structural gene encoding a protein, or complementary binding of the nucleotide sequence to at least a part of the structural gene, thus typically reducing the quantity of the protein in the cell.
  • the present positive selection method in vivo is of particular relevance, for example, in connection with transformation performed on whole plants or on plant parts, in which the plants or parts comprise both transformed and non-transformed cells, since selection of the transformed cells is achieved without directly damaging the neighboring non-transformed cells.
  • the transformed cells thus have a selective "advantage" compared to the non-transformed cells (e.g. the ability to thrive and grow; in plants, e.g., the ability to form shoots, etc.), but the non-transformed cells do not suffer any severe disadvantage in the sense of being damaged or killed, as in the case with negative selection using antibiotics or herbicides.
  • the selective advantage possessed by the transformed cells may typically be a difference or advantage allowing the transformed cells to be identified by simple visual means, i.e. without the use of a separate assay to determine the presence of a marker gene.
  • a population of cells may be cultivated on or in a medium containing at least one compound which may be inactive and which is directly or indirectly activated in the transformed cells, the compound being inactive in non-transformed cells or less active in non-transformed cells than in transformed cells, such that the transformed cells are provided with a selective advantage allowing them to be selected from the cell population.
  • the population of cells may also be cultivated on or in a medium containing a compound which is made available for the transformed cells by expression or transcription of the nucleotide sequence, the compound not being available for the non- transformed cells or being less available for non-transformed cells, such that the transformed cells are provided with a selective advantage.
  • the cells may also be transformed with a selectable marker gene which may encode a permease or other transport factor which allows the marker compound to cross the cell membrane and enter the transformed cells or to cross another (organelle) membrane, so that "activation" of an inactive compound involves selective uptake of the compound by transformed cells, and uptake by non-transformed cells is not possible or takes place to a lesser extent.
  • a selectable marker gene which may encode a permease or other transport factor which allows the marker compound to cross the cell membrane and enter the transformed cells or to cross another (organelle) membrane, so that "activation" of an inactive compound involves selective uptake of the compound by transformed cells, and uptake by non-transformed cells is not possible or takes place to a lesser extent.
  • the positive selection gene may alternatively direct its product to a compartment in which the inactive compound is located, for example, outside the plasma membrane or into the vacuole or the endoplasmic reticulum.
  • a compound used for selection purposes may in addition have both a positive and a negative effect.
  • certain carbon sources in sufficiently high concentrations can be toxic to most plants, but in cells containing arabitol or ribitol metabolizing enzymes, the negative effect is eliminated and the cells further obtain the benefit of being able to use these compounds as a carbohydrate source.
  • a single compound and a single or group genes together provide a combined positive and negative selection system, although such a system may also be established using two or more genes which together are responsible for inhibition of the negative effects of a compound and manifestation of the positive effects of the compound in the transformed cells.
  • the cells may be transformed with any nucleotide sequence which it is desired to incorporate therein to.
  • a nucleotide sequence may encode genes providing for viral, fungal, bacterial or nematode resistance.
  • the protein encoded by the gene of interest or preferably the selectable marker gene is preferably an enzyme involved in arabitol or ribitol metabolism.
  • Such enzymes include ribitol or D-arabitol dehydrogenease, ribitol or D-arabitol kinase, or D-ribitol or D-arabitol transporter gene. Scangos and Reiner, Journal of Bacteriology, 134:492-500 (1978).
  • Examples of compounds which can exert a physiological effect upon entering the cell, but which are not easily taken up into the cell or a cell compartment, are strongly hydrophilic or hydrophobic compounds, in particular charged compounds, large molecules such as polymers, in particular proteins, peptides, oligo- and polysaccharides, including plant hormones, phosphorylated metabolites such as phosphorylated carbohydrates, phosphorylated vitamins, phosphorylated nucleosides, including cytokinins, and compounds which are conjugated to carboxylic acid- containing carbohydrates or amino acids, including plant hormone conjugates.
  • the basic method of the present invention may be modified so that, instead of activating an inactive compound or nutrient in the transformed cells, selection may be performed by blocking the metabolism or synthesis of a compound in these cells.
  • the non-transformed cells may in certain cases contain or produce a certain amount of the polypeptide in question.
  • the activating polypeptide is an enzyme
  • the non-transformed cells may contain a certain native enzyme activity, the native enzyme being of the same type as the introduced activating enzyme.
  • the "inactive compound or nutrient" need not necessarily be completely inactive in the non- transformed cells, since it may be sufficient that the compound or nutrient is merely substantially less active in non-transformed cells than in transformed cells.
  • a qualitative difference between the transformed cells and the non-transformed cells with regard to activation of the initially inactive compound or nutrient may in certain cases be sufficient for selection purposes, h such cases inhibitors or substrates which compete with the native enzymes may be added.
  • inhibitors or substrates which compete with the native enzymes may be added.
  • inhibitors activated by the native enzyme resulting in self-catalyzed production of the active inhibitor to a level at which the native enzyme is substantially totally inhibited.
  • the transformation contemplates constructing a vector comprising a gene of interest and a selectable marker gene, placing the vector into a selected strain of Agrobacterium, and treating selected plant cells with the Agrobacterium under conditions sufficient to result in transfer of at least some of the vectors from the Agrobacterium to the plant cells, whereby the polynucleotide is expressed in the plant cells.
  • Regulatory sequences can include both promoter and termination sequences.
  • Possible regulatory sequences can include, but are not limited to, any promoter already shown to be constitutive for expression, such as those of viral origin (CaMV 19S and 35S, TMV, AMV) or so-called "housekeeping" genes (ubiquitin, actin, tubulin) with their corresponding termination/poly A + sequences.
  • seed-and/or developmentally-specific promoters such as those from plant fatty acid/lipid biosynthesis genes (ACPs, acyltransferases, desaturases, lipid transfer protein genes) or from storage protein genes (zein, napin, cruciferin, conglycinin, or lectin genes, for example), with their corresponding termination/poly A + sequences can be used for targeted expression.
  • the gene can be placed under the regulation of inducible promoters and their termination sequences so that gene expression is induced by light (rbcS-3A, cab-1), heat (hsp gene promoters) or wounding (mannopine, HGPGs).
  • a promoter may be used either in native or truncated form, and may be paired with its own or a heterologous termination polyA + sequence.
  • Plant tissue for use in transformation may be obtained from any suitable plant, i.e., known to be susceptible to transformation by known methods.
  • Appropriate plant tissue includes, but is not limited to, leaves, hypocotyls, cotyledons, stems, callus, single cells, and protoplasts.
  • transformed callus tissue is selected by growth on selection medium (e.g., medium which contains carbon source only utilizable by transformed plant cells).
  • Selection medium e.g., medium which contains carbon source only utilizable by transformed plant cells.
  • Transformed plants are regenerated and screened for the presence of the gene of interest. This involves analyzing tissue by at least one molecular or biological assays to determine which, if any, transformants contained the gene of interest. These assays include assays or observation of the tissue for growth, and assays of the tissue for the presence of gene of interest by, for example, a Southern assay or a PCR assay.
  • tissue can be analyzed for the expression of the gene of interest by looking for the polypeptide encoded by the polynucleotide, as for example via a Western blot analysis, and for the phenotype conferred to the plant by the gene of interest.
  • frequency of preferred codon usage refers to the preference exhibited by a specific host cell in usage of nucleotide codons to specify a given amino acid. To determine the frequency of usage of a particular codon in a gene, the number of occurrences of that codon in the gene is divided by the total number of occurrences of all codons specifying the same amino acid in the gene. Similarly, the frequency of preferred codon usage exhibited by a plant cell can be calculated by averaging frequency of preferred codon usage in a large number of genes expressed by the plant cell. It is preferable that this analysis be limited to genes that are highly expressed by the host cell.
  • plant cells can be genetically engineered, e.g., transformed with genetic contracts to attain desired expression levels of the gene of interest.
  • the DNA sequence of the gene of interest can be modified to comprise codons preferred by highly expressed genes to attain an A+T content in nucleotide base composition which is substantially that found in the transformed host cell. It is also preferable to form an initiation sequence optimal for said plant cell, and to eliminate sequences that cause destabilization, inappropriate polyadenylation, degradation and termination of RNA and to avoid sequences that constitute secondary structure hairpins and RNA splice sites.
  • the codons used to specify a given amino acid can be selected with regard to the distribution frequency of codon usage employed in highly expressed genes in the plant cell to specify that amino acid.
  • the distribution frequency of codon usage utilized in the synthetic gene is a determinant of the level of expression.
  • the selectable marker genes pertain to SEQ ID NO.: 1 and SEQ ID NO.:2 as well as fragments or functional mutants thereof that are capable of metabolizing a marker compound to confer a selective advantage.
  • Such fragments and mutants will be readily obtainable following the teachings herein coupled with the state of the art.
  • useful polynucleotides can be obtained under conditions of appropriate stringency.
  • the present invention further relates to variants of the present polynucleotides which encode for fragments, analogs and derivatives of the polypeptides having the sequences shown in SEQ ID NO.: 3, SEQ ID NO.:4, and SEQ TD NO.:5.
  • a variant of the polynucleotide may be a naturally occurring variant such as a naturally occurring allelic variant, or it may be a variant that is not known to occur naturally.
  • Such non-naturally occurring variants of the polynucleotide may be made by mutagenesis techniques, including those applied topolynucleotides, cells or organisms.
  • variants in this regard are variants that differ from the aforementioned polynucleotides by nucleotide substitutions, deletions or additions. The substitutions may involve one or more nucleotides.
  • the variants may be altered in coding or non- coding regions or both. Alterations in the coding regions may produce conservative or non-conservative amino acid substitutions, deletions or additions.
  • polynucleotides encoding polypeptides having the amino acid sequences shown in SEQ TD NO.: 3, SEQ TD NO.:4, and SEQ TD NO.:5; variants, analogs, derivatives and fragments thereof.
  • polynucleotides encoding one or more gene products of the ribitol or arabitol operons (e.g., RtlT, RtlK, RtlD, RtIR, AtlD proteins), or combinations thereof, and fragments, and variants, analogs and derivatives of the fragments, which have the amino acid sequences exemplified herein in which several, a few, 1 to 10, 1 to 5, 1 to 3, 2, 1 or no amino acid residues are substituted, deleted or added, in any combination.
  • silent substitutions, additions and deletions which do not alter the properties and activities of the proteins.
  • conservative substitutions are also especially preferred in this regard.
  • polynucleotides that are greater than 79%, preferably at least 85%, more preferably at least 90% identical to a polynucleotide encoding SEQ ID NO.: 1 and SEQ ID NO.:2, and polynucleotides which are complementary to such polynucleotides.
  • these particularly preferred polynucleotides those with at least 90%, 95%, 98% or at least 99% identity are especially preferred.
  • Particularly preferred embodiments in this respect are polynucleotides which encode polypeptides which retain substantially the same or even exhibit a reduction in the biological function or activity as the mature polypeptide encoded by the polynucleotides described above.
  • the present invention further relates to polynucleotides that hybridize to the herein above-described sequences.
  • the present invention especially relates to polynucleotides which hybridize under stringent conditions to the herein above-described polynucleotides.
  • a preferred level of stringency is such that hybridization will only occur if there is at least 85 %>, and preferably still 90%, and more preferably 95%, and even more preferably 97%) identity between the sequences.
  • identity and similarity are relationships between two polypeptide sequences or two polynucleotide sequences, as determined by comparing the sequences, h the art, identity also means the degree of sequence relatedness between two polypeptide or two polynucleotide sequences as determined by the match between two strings of such sequences. Both identity and similarity can be readily calculated (Computational Molecular Biology, Lesk, A.M., ed., Oxford University Press, New York, 1988; Biocomputing: Informatics and Genome Projects, Smith, D. W., ed., Academic Press, New York, 1993; Computer Analysis of Sequence Data, Part I, Griffin, A. M., and Griffin, H.
  • Typical computer program methods to determine identity and similarity between two sequences include, GCG program package (Devereux, J., et al., Nucleic Acids Research 12(1):387 (1984)), BLASTP, BLASTN, FASTA and TFASTA (Atschul, S. F. et al, J. Mol. Biol. 215:403 (1990)).
  • stringent conditions or “stringent hybridization conditions” includes reference to conditions under which a probe will hybridize to its target sequence, to a detectably greater degree than other sequences (e.g., at least 2-fold over background). Stringent conditions are sequence-dependent and will be different in different circumstances. By controlling the stringency of the hybridization and/or washing conditions, target sequences can be identified which are 100%> complementary to the probe (homologous probing). Alternatively, stringency conditions can be adjusted to allow some mismatching in sequences so that lower degrees of similarity are detected (heterologous probing). Generally, a probe is less than about 1000 nucleotides in length, preferably less than 500 nucleotides in length.
  • stringent conditions will be those in which the salt concentration is less than about 1.5M Na ion, typically about 0.01 to 1.0M Na ion concentration (or other salts) at pH 7.0 to 8.3 and the temperature is at least about 30° C for short probes (e.g., 10 to 50 nucleotides) and at least about 60°C for long probes (e.g., greater than 50 nucleotides).
  • Stringent conditions may also be achieved with the addition of destabilizing agents such as formamide.
  • Exemplary low stringency conditions include hybridization with a buffer solution of 30 to 35% formamide, IM NaCl, 1% SDS (sodium dodecyl sulfate) at 37° C, and a wash in IX to 2X SSC (20X SSC-3.0M NaCl/0.3M trisodium citrate) at 50 to 55° C.
  • Exemplary moderate stringency conditions include hybridization in 40 to 45% formamide, IM NaCl, 1% SDS at 37° C, and a wash in 0.5X to IX SSC at 55 to 60° C.
  • Exemplary high stringency conditions include hybridization in 50% formamide, IM NaCl, 1% SDS at 37° C, and a wash in 0.1X SSC at 60 to 65° C.
  • the T m is the temperature (under defined ionic strength and pH) at which 50% of a complementary target sequence hybridizes to a perfectly matched probe. T m is reduced by about 1° C. for each 1% of mismatching; thus, T m , hybridization and/or wash conditions can be adjusted to hybridize to sequences of the desired identity. For example, if sequences with 90% identity are sought, the T m can be decreased 10° C. Generally, stringent conditions are selected to be about 5° C lower than the thermal melting point (T m ) for the specific sequence and its complement at a defined ionic strength and pH.
  • Example 1 Transformation of E. coli with rtl operon and growth on ribitol medium
  • the K. pneumoniae fragments were released yia enzymatic digestion as recommended by the manufacturer (NEB, Beverly, MA), and blunted into the Stul site of pMECA (Thomson and Parrott 1998).
  • E. coli strain C which was obtained as stock number 3121 from the E. coli Genetic Stock Center at Yale University, and grown in 2B minimal broth supplemented with 2 g l "1 of ribitol.
  • Total genomic DNA was isolated according to Syn and Swarup (2000). The genomic DNA was subject to digestion by Cla ⁇ . Following T4 DNA ligation into the corresponding site of pHEX3 (Heuel et al. 1997) and transformation into DH10B, incubation took place in 5 ml of 2B minimal broth supplemented as described previously. After 24 hours, 1 ml was placed in 25 ml of the same medium.
  • bacterial colonies were obtained following plating an aliquot of the liquid medium onto plates with solid LB medium supplemented with 20 mg l "1 chloramphenicol. A single colony was grown in TB , and plasmid DNA isolated using a QuantumPrep kit (Biorad, Hercules, CA) and sequenced using a Model 377 automated DNA sequencer (PE Applied Biosystems, Forster City, CA) by the University of Georgia Molecular Genetics Instrumentation Facility. Sequence comparisons were made using the on-line BLAST programs of the National Center for Biotechnology Information (Bethesda, MD), and the GAP program of the Wisconsin Package, ver.
  • Ligated plasmids were transformed into DH10B and grown in 2B minimal broth supplemented with 2 g l "1 of ribitol.
  • the 2B medium was additionally supplemented with 50 mg l "1 each of L- leucine and L-isoleucine, and 1 mg 1 _1 thiamine.
  • the resulting plasmids were named pMECA-R and pBluescript-R. Plasmid maps were drawn with Plasmid 1.1 (Redasoft, Toronto, Canada).
  • pMECA growth rates and plasmid yields were compared for pMECA, pMECA-R, pBluescript, and pBluescript-R in DHIOB .
  • Both pMECA and pBluescript were grown in LB broth and in 2B minimal broth supplemented with 2 g 1 _1 glucose.
  • pMECA-R and pBluescript-R were grown in 2B minimal broth supplemented as described above.
  • Bacteria were inoculated into 2 ml of their respective media, allowed to grow for 17 or 41 hours, and plasmid DNA isolated as described previously. Plasmid yield was quantified with a DNA fluorometer (Hoefer Scientific, San Francisco, CA). Each treatment was repeated three times.
  • Plasmid yields were also quantified for pMECA-R and pBluescript-R containing an insert in their MCSs.
  • a Psi ⁇ /Ascl fragment from pTFG containing the cauliflower mosaic virus 35S promoter-GUS-nos terminator construct out of pTRA140 (Zheng et al. 1991) was ligated into the Pstl and Ascl sites of pMECA-R and a Pstl- Stul fragment of pTFG into the Pstl and EcoRV sites of pBluescript-R.
  • the ligated plasmids were transformed into DHIOB, cultured, isolated, and quantified as described above.
  • the ribitol operon from E. coli C contains 4 genes, in order as follows: rtlR, rtlD, rtlK, and rtlT.
  • the first is a repressor, and contains the promoter for the operon.
  • RtlD codes for NAD-dependent ribose dehydrogenase which converts ribose to D- ribulose.
  • RtlK codes for ATP-dependent ribulose kinase, which converts D-ribulose to D-ribulose-5 -phosphate, and which can be metabolized by all E. coli strains.
  • rtlT codes for a ribose-specific ion symporter protein (Heuel et al. 1998).
  • the bla gene is only 788 bp long, in contrast to rtlK, rtlD, and rtlT, which are collectively 3971 bp long. We were able to compensate to some extent for the size difference by eliminating some of the DNA flanking the bla gene. Nevertheless, pMECA-R is 31683 bp larger than pMECA, and pBluescript-R is 3032 bp larger than pBluescript. Replacing bla with rtlD, rtlK, and rtlT inevitably brought along enzyme sites which led' to the loss of uniqueness of enzyme sites within the pMECA and pBluescript MCSs. Nevertheless, pMECA-R still has 30 unique sites, while pBluescript-R has 18 unique sites. These are listed in Table 2.
  • Plasmid yields for DH10B are depicted i Figure 2. Heuel et al. (1998) reported that high-copy number plasmids containing dal or rbt were unstable under arabitol or ribitol selection, but we did not experience any such difficulties.
  • yields were higher in 2B minimal medium than in the standard LB broth. Yields of the ribitol version were essentially like those of the ampicillin version when grown in minimal medium. On a molar basis, yields in 2B minimal medium with ribitol are lower than those in 2B minimal medium with glucose, as the ribitol version ofpBluescri.pt is twice as large as the ampicillin version. Insertion of a GUS construct into the MCS did not significantly affect plasmid yield.
  • the K-12 strains in use today have an absolute requirement for essential nutrients in the growth medium, as the parent strain has been subject to extensive mutagenesis since its isolation in 1922 (Bachmann 1972). Since different K-12 strains have different growth requirements, minimal growth medium must be adjusted for each K-12 strain by adding the necessary nutrients that each particular strain requires.
  • pMECA A cloning plasmid with 44 unique restriction sites that allows selection of recombinants based on colony size.
  • Example 2 Isolation and Sequencing of Arabitol Dehydrogenase Total genomic DNA was isolated from E. coli strain C, digested with Pstl, the resulting fragments were ligated into pBluescript, and transformed into E. coli DHIOB. The E. coli was then grown on 2B Minimal Medium as described by LaFayette and Parrott (2001; A non antibiotic marker for amplification of plant transformation vectors in E. coli. Plant Cell Rep, In press), except that arabitol was substituted for ribitol.
  • the EZ::TN Insertion Kit from Epicentre Technologies was used. Primer sites on the TN transposon were used to determine which colonies had inserts in the arabitol operon, and which had them in the vector sequence. Plasmid was isolated from four colonies with transposon insertions in the arabitol operon, and the primer sites on the transposon used to amplify the insert fragments. These were sent for sequencing at the University of Georgia's Molecular Genetics Instrumentation Facility. The resulting sequences were assembled using BLAST to align the regions homologous to the enzyme counterparts in P. klebsiella. The sequence was determined to be the arabitol dehydrogenase gene (SEQ ID NO. 1). The second DNA strand was sequenced, and the resulting sequence was used to verify the sequence of the first strand.
  • Example 3 Transformation of Plant cells rbt or dal operon.
  • Somatic embryos of Jack, a Glycine max (L.) Merrill cultivar with high embryogenic capacity are induced from immature cotyledons, proliferated and maintained. See, as described by, Samoylov et al., Plant Cell Rep 18:49-54; Bailey et al., In Vitro-Plant. 29P:102-108 (1993); and Bailey et al., Plant Sci. 93:117-120 (1993).
  • clumps of globular-stage embryos are bombarded. The average clump diameter is 2 mm.
  • Plasmid DNA produced by the procedures in Examples 1 and/or 2 is isolated using an alkalinelysis/ PEGpurification procedure (Yeung and Lau, Biotechniques. 15(3):381-2 (1993)), and is preferably coupled with a known promoter according to standard protocols. Plasmid DNA is suspended at equimolar amounts in a final concentration of 1 ⁇ g/L and precipitated onto 1- ⁇ m gold particles according to conventional protocols (see, e.g., Christou et al., Plant Physiology 87:671-674 (1988). The Bio-Rad PDS 1000H is used for bombardment. Each plate is bombarded twice using 650-psi rupture discs supplied by Bio-Rad in a 700-mm mercury vacuum.
  • embryos are transferred to an open Petri dish and desiccated for 15 min and then mashed gently with a spatula. Ten plates of somatic embryos (1 g per plate) are bombarded. Following bombardment, embryos are dried for 30 min in a covered Petri dish. The embryos are subsequently transferred to MSD20 medium (Bailey et al., 1993, supra).
  • MSD20 medium Green et al., 1993, supra.
  • Agrobacterium harboring a vector containing SEQ ID NO 1 or nucleotide sequences encoding the polypeptides shown in SEQ ID NOS: 3, 4, and/or 5 are used to transfer shoot segments according to standard protocols.
  • Example 4 Selection of Transgenic Plant cells using Arabitol or Ribitol as Selectable Markers and Plant Regeneration
  • the arabitol, ribitol, mannitol is provided in equimolar amounts with the sucrose in the MSD20 medium. Transfers to fresh medium are made every 3 weeks.
  • surviving embryonic clusters are transfened to liquid FN medium (Samoylov et al, In Vitro Cell Dev. Biol- Plant 34:8-13 (1998)).
  • putative transgenic cell lines are separated and tracked. Cells are allowed to acclimate for 4 weeks with a transfer to fresh medium after 2 weeks. Then, the clusters are transferred to FN containing arabitol or ribitol (0-25 g/L) for 2 weeks of final selection.
  • the transgenic somatic embryos are germinated and converted using previously published methods (Bailey et al., 1993, supra).
  • the To plants are grown in 4-L pots in a sand: loam:bark mixture (1:1:1, w/w Hyponex MaryviUe, OH) under 23-h photoperiods (for vegetative growth) for 2 months in a glass greenhouse. Flowers are induced using 12- h photoperiods for the duration of the plants' life cycle.
  • the Ti plants are grown under similar conditions.
  • the final medium contains 100 ml of 2B stock I, 50 ml of 2B stock II, and 20 ml of 2B stock III per liter.

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Abstract

L'invention porte sur de nouveaux procédés et matériaux de sélection de cellules transgéniques et en particulier sur des méthodes de sélection positive consistant à conférer à certaines cellules la capacité de métaboliser certains composés dont de préférence l'arabitol, le ribitol, la raffinose, le saccharose, le mannitol ou leurs combinaisons. On peut de ce fait sélectionner des cellules transformées en les soumettant simplement à un milieu contenant de tels composés. Ladite invention, qui atténue les désavantages et problèmes des méthodes de sélection négative, tels que la destruction inutile des cellules transformées, et la dispersion dans l'environnement de gènes potentiellement nuisibles (par exemple gènes résistants aux antibiotiques ou aux herbicide), porte en outre sur de nouvelles séquences nucléotidiques relatives à l'opéron du E. Coli rtl et au gène de l'arabitol déshydrogénase, et sur des séquences d'acides aminés relatives à leurs produits géniques.
PCT/US2001/007474 2000-03-08 2001-03-08 L'arabitol ou le ribitol, marqueurs par selection positive WO2001066779A2 (fr)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994020627A1 (fr) * 1993-03-02 1994-09-15 Sandoz Ltd. Selection positive a base de mannose ou de xylose
WO1997044448A1 (fr) * 1996-05-17 1997-11-27 Pioneer Hi-Bred International, Inc. Elements promoteurs conferant une expression genique dans les racines de maniere preferentielle.

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994020627A1 (fr) * 1993-03-02 1994-09-15 Sandoz Ltd. Selection positive a base de mannose ou de xylose
WO1997044448A1 (fr) * 1996-05-17 1997-11-27 Pioneer Hi-Bred International, Inc. Elements promoteurs conferant une expression genique dans les racines de maniere preferentielle.

Non-Patent Citations (12)

* Cited by examiner, † Cited by third party
Title
BARTKUS J M ET AL: "CONSTRUCTION OF AN IMPROVED D-ARABINOSE PATHWAY IN ESCHERICHIA COLI K-12" JOURNAL OF BACTERIOLOGY, WASHINGTON, DC, US, vol. 165, no. 3, March 1986 (1986-03), pages 704-709, XP001051850 ISSN: 0021-9193 *
BRUNKER P ET AL: "Structure and function of the genes involved in mannitol, arabitol and glucitol utilization from Pseudomonas fluorescens DSM50106" GENE: AN INTERNATIONAL JOURNAL ON GENES AND GENOMES, ELSEVIER SCIENCE PUBLISHERS, BARKING, GB, vol. 206, no. 1, 5 January 1998 (1998-01-05), pages 117-126, XP004102880 ISSN: 0378-1119 *
HEUEL H ET AL: "Genes for D-arabinitol and ribitol catabolism from Klebsiella pneumoniae." MICROBIOLOGY (READING), vol. 144, no. 6, June 1998 (1998-06), pages 1631-1639, XP002200661 ISSN: 1350-0872 *
HEUEL HANSJOACHIM ET AL: "Substrate recognition domains as revealed by active hybrids between the D-arabinitol and ribitol transporters from Klebsiella pneumoniae." JOURNAL OF BACTERIOLOGY, vol. 179, no. 19, 1997, pages 6014-6019, XP002200662 ISSN: 0021-9193 *
LAFAYETTE P R ET AL: "A non-antibiotic marker for amplification of plant transformation vectors in E. coli." PLANT CELL REPORTS, vol. 20, no. 4, June 2001 (2001-06), pages 338-342, XP002200660 ISSN: 0721-7714 *
LINK C D ET AL: "GENOTYPIC EXCLUSION: A NOVEL RELATIONSHIP BETWEEN THE RIBITOL-ARABITOL AND GALACTITOL GENES OF E. COLI" MOLECULAR AND GENERAL GENETICS, SPRINGER VERLAG, BERLIN,, DE, vol. 189, 1983, pages 337-339, XP001051839 ISSN: 0026-8925 *
LINK C D ET AL: "INVERTED REPEATS SURROUND THE RIBITOL-ARABITOL GENES OF E.COLI C" NATURE, vol. 298, 1 July 1982 (1982-07-01), pages 94-96, XP001042180 ISSN: 0547-051X *
LOVINY T ET AL: "RIBITOL DEHYDROGENASE OF KLEBSIELLA-AEROGENES SEQUENCE OF THE STRUCTURAL GENE" BIOCHEMICAL JOURNAL, vol. 230, no. 3, 1985, pages 579-586, XP008003567 ISSN: 0264-6021 *
POSTMA P W ET AL: "PHOSPHOENOLPYRUVATE: CARBOHYDRATE PHOSPHOTRANSFERASE SYSTEMS OF BACTERIA" MICROBIOLOGICAL REVIEWS, AMERICAN SOCIETY FOR MICROBIOLOGY, WASHINGTON, DC, US, vol. 57, no. 3, September 1993 (1993-09), pages 543-594, XP001051826 ISSN: 0146-0749 *
SCANGOS G A ET AL: "RIBITOL AND D-ARABITOL CATABOLISM IN ESCHERICHIA COLI" JOURNAL OF BACTERIOLOGY, WASHINGTON, DC, US, vol. 134, no. 2, May 1978 (1978-05), pages 492-500, XP001051858 ISSN: 0021-9193 *
TRIMBUR D E ET AL: "ISOLATION AND CHARACTERIZATION OF ESCHERICHIA COLI MUTANTS ABLE TO UTILIZE THE NOVEL PENTOSE L-RIBOSE" JOURNAL OF BACTERIOLOGY, WASHINGTON, DC, US, vol. 173, no. 8, 1991, pages 2459-2464, XP002056778 ISSN: 0021-9193 *
WONG B ET AL: "D-ARABITOL METABOLISM IN CANDIDA ALBICANS: STUDIES OF THE BIOSYNTHETIC PATHWAY AND THE GENE THAT ENCODES NAD-DEPENDENT D-ARABITOL DEHYDROGENASE" JOURNAL OF BACTERIOLOGY, WASHINGTON, DC, US, vol. 175, no. 19, 1 October 1993 (1993-10-01), pages 6314-6320, XP002059303 ISSN: 0021-9193 *

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