IMPROVED METHOD FOR <i>AGROBACTERIUM</i> MEDIATED TRANSFORMATION OF COTTON

Abstract: This invention relates to improved methods for the production of transgenic cotton plants, comprising cocultivating <i>Agrobacterium</i> cells comprising a DNA fragment of interest operably linked to at least one T-DNA border with cotton embryogenic callus in the presence of a plant phenolic compound.

Description: IMPROVED METHOD FOR AGROBACTERIUM MEDIATED TRANSFORMATION OF COTTON. This invention relates to the field of plant transformation, particularly to an improved method for Agrobactenum mediated transformation of cotton. Cotton is an important crop, grown primarily for its lint, which provides much of the high quality fiber for the textile industry. Cotton seed is also a valuable commodity, as it provides a source for oil, meal and seed hulls. About 90 % of cotton grown worldwide is Gossypium hirsutum L, whereas Gossypium barbadense accounts for the about 8 %. Improvement of various traits such as resistance to pests, stress or disease, fiber quality, reduced gossypol content, has been obtained by conventional breeding techniques, and further improvement of these and other traits can be achieved using molecular and genetic techniques. Several methods are available for the transformation of cotton including Agrobactenum mediated transformation of cotton expiants, such as isolated cotyledons, isolated hypocotyls and isolated hypocotyl transition zones, as well as direct gene transfer by microprojectile bombardment of meristimatic cotton tissues. Firoozabady et al. (1987, Plant Molecular Biology 10:105-116) described transformation of cotton cotyledon tissues by Agrobactenum tumefaciens and regeneration of transgenic plants. Umbeck et al. (1987, Bio/Technology 5: 263-266) reported results on cotton transformation via Agrobactenum using hypocotyls as expiants. PCT publication ("WO") 89/05344, US patent ("US") 5, 244,802 and US 5,583,036 provide methods for regeneration of cotton by tissue and suspension culture starting with expiants which are the hypocotyl, cotyledon or immature embryos Also taught are method to transform cotton and improve cotton by selective growth WO 89/12102 and US 5,164,310 relate to a novel method for transforming and rapidly regenerating plant tissue The method employs target tissues which are the shoot apices thereby expanding the species range for transformation and reducing the risk of somaclonal variation WO 98/15622 provides a method for the in vitro regeneration of fertile Gossypium plants in which cells from the transition region tissue of seedlings is excised and cultured A method for the production of transgemc Gossypium plants capable of transmitting a foreign gene to progeny is also described in which cells derived from the transition region tissue of seedlings are targeted for transformation WO 97/12512 provides a method for regenerating cotton plants from explant tissue which allows the generation of embryogenic callus from a cotton tissue explant, such as a hypocotyl, which is not cultivated on callus initiation media having exogenous plant hormones The method can be utilized in the transformation of cotton plants US 5,004,863 and US 5,159,135 and European patent publication "EP" 0 270 355 all disclose a method to achieve genetic transformation of cotton plants and lines, by subjecting immature cotton tissues such as hypocotyl segments in vitro to Agrobactenum mediated genetic transformation WO 97/43430 relates to a versatile method of rapidly regenerating cotton plants from expiants of apical and/or nodal meπstematic tissues which can be coupled with well known methods of transformation such as Agrobacterium- mediated transformation for the rapid production of genetically-engineered cotton varieties of agronomic importance WO 92/15675 and EP 0 531 506 describe a method for the particle-mediated transformation of cotton permitting the direct genetic engineering of elite cotton lines without the need for tissue culture or callus proliferation involving excision of the embryonic axes from germinating seeds and blasting particles carrying foreign genes into the embryonic axes Finer and Mc Mullen (1990 Plant Cell Reports 8 586-589) described transformation of cotton via particle bombardment of embryogemc suspension cultures McCabe and Martmell, (1993, Bio/Technology 11 596-598) have described transformation of elite cotton cultivars via particle bombardment of cotton meπstematic tissue from excised embryonic axes Hansen ef a/ (1994, Proc Natl Acad Sci 91 7603-7607) have described an Agrobactenum strain comprising a constitutive virG mutant (w/GN54D) leading to enhanced transformation efficiencies of isolated cotton cotyledons. Veluthambi et al (1989, Journal of Bacteriology 171 3696-3703) described a markedly increased transformation of cotton shoot tips by the simultaneous addition of acetosynngone and nopaline at the time of infection The cotton transformation methods of the prior art suffer from the major drawback, as indicated in Murray et al (1993, in Transgemc Plants Vol 2, Academic Press Inc p153-168) that the time required to regenerate a transgemc plant from an explant which has been cocultivated with Agrobactenum cells is extremely long Moreover, an additional problem arises from the fact that all described Agrobactenum mediated transformation methods of cotton require the generation of embryogemc callus from the explant containing the transformed cells, as an intermediate step in the regeneration of transgemc cotton plants Since not all transformed cells of the explant necessarily are competent for the initiation of embryogemc callus a loss of regeneration of a number of potentially transgemc cells, which consequently results in a low transformation efficiency, is observed with these methods An increase in starting numbers of putative transformed cotton expiants to compensate for this loss, results in an huge increase of the amount of labor to be invested in obtaining regenerated transgemc cotton plants WO 89/05344 has suggested in general terms that embryogemc callus may be used as appropriate starting material for Agrobactenum mediated transformation of cotton callus Nevertheless during the past decade no reports were made of successful production of transgemc cotton plants using cocultivation of embryogemc callus with Agrobactenum To some extent the problem has been alleviated by techniques in microprojectile bombardment of meπstematic tissue which results in a larger number of transgemc cotton lines Nonetheless, the generation of germhne transformed cotton plants, which are capable of passing on the transgene to their progeny, is infrequent The art is thus deficient in providing an efficient method, both in term of required time and transformation efficiency, for the generation of transgemc cotton plants which are capable of transferring the foreign incorporated DNA to their progeny plants Summary and objects of the invention In view of the foregoing shortcomings associated with prior art cotton transformation processes as well as other disadvantages not specifically mentioned above, it should be apparent that there still exists a need in the art for a method of transforming cotton which achieves the heretofore elusive combination of a high transformation efficiency in a relatively short period of time It is therefore a primary objective of the present invention to fulfill that need by providing a method for producing a transge c cotton plant, preferably a fertile transgemc plant, by /4gro£>ac.eπum-medιated transformation, comprising cocultivating Agrobactenum cells comprising a DNA fragment of interest operably linked to at least one T-DNA border with cotton embryogemc callus in the presence of a plant phenolic compound It is another object of the invention to provide a method for producing a transgemc cotton plant which eliminates the step of generating embryogemc callus from a cotton explant comprising the transformed cells, thereby both reducing the potential loss of transformed cotton lines from transformed plant cells which are not capable of generating embryogemc callus, and in this way enhancing transformation frequencies In a first aspect, the present invention relates to a method for producing a transgemc cotton plant comprising incubation of Agrobactenum cells comprising a DNA fragment of interest operably linked to at least one T-DNA border, with a plant phenolic compound prior to or during the co-cultivation of cotton embryogemc callus with the Agrobactenum cells. In another aspect, the present invention relates to a method for producing a transgemc cotton plant, comprising. i) cocultivating cotton embryoge c callus preferably derived from a hypocotyl of a cotton seedling, with Agrobactenum cells, the Agrobactenum cells comprising a DNA fragment of interest operably linked to at least one T-DNA border, in the presence of a plant phenolic compound, preferably selected from the group consisting of acetosyπngone, α-hydroxy-acetosynngone, sinapimc acid, syπngic acid, ferulic acid catechol, p-hydroxybenzoic acid, β- resorcylic acid, protocatechuic acid, pyrrogallic acid, gallic acid and vanillin, preferably present in a concentration range from about 50 μM to about 400 μM, for a time sufficient to generate embryogemc callus comprising a transformed cotton cell, preferably for about 3 to 4 days; n) regenerating a transgemc cotton plant from said transformed cell; and optionally in) crossing said transgemc cotton plant with another cotton plant In another aspect, the invention relates to the use of a plant phenolic compound, preferably acetosynngone for Agrobactenum mediated transformation of cotton embryogemc callus Detailed description of the invention The inventors have developed an improved and accelerated Agrobactenum mediated transformation method for the production of transge c cotton plants, comprising the use of a plant phenolic compound, such as acetosyπngone, duπng Agrobactenum mediated transformation of cotton embryogemc callus, preferably during the cocultivation stage of cotton embryogemc callus with Agrobactenum cells This method on average leads to a time reduction in the period starting from cocultivation towards the time point at which the transgemc cotton plant is sufficiently developed to be transferred to soil, preferably under greennouse conditions, of at least about 2 to 3 months Since the improved method of this invention comprises the use of embryogemc callus as starting tissue for the transformation, the step of generating embryogemc callus from the cotton explant comprising the transformed cells is eliminated Consequently, the potential loss of transformed cotton lines from transformed plant cells which are not capable to generate embryogemc callus is reduced, and transformation frequencies are enhanced Moreover, embryogemc callus, once initiated can be maintained straightforwardly (as long as somaclonal variation does not interfere with phenotype of regenerated plants) thus facilitating the management of the supply of starting material for transformation experiments Indeed, the inventors have surprisingly found that Agrobactenum mediated transformation of cotton embryogemc callus, necessitated the addition of a plant phenolic compound, such as but not limited to acetosyπngone, preferably at the cocultivation stage Nowhere in the prior art has it been suggested that the inclusion of such a plant phenolic compound, of all possible variables would lead to successful Agrobactenum mediated transformation of cotton embryogemc callus In one embodiment, the invention relates to the use of a plant phenolic compound during the ατo£>acte/7i-/π7-medιated transformation of cotton embryogemc callus "Plant phenolic compounds" or ' plant phenolics suitable for the invention are those substituted phenolic molecules which are capable to induce a positive chemotactic response, particularly those who are capable to induce increased wr gene expression in a Ti-plasmid containing Agrobactenum sp , particularly a Ti-plasmid containing Agrobactenum tumefaciens Methods for measuring chemotactic response towards plant phenolic compounds have been described by Ashby et al (1988 J Bactenol 170 4181 -4187) and methods to measure induction of vir gene expression are also well known (Stachel et al., 1985 Nature 318 624-629, Bolton et al 1986, Science 232 983-985) Preferred plant phenolic compounds are those found in wound exudates of plant cells One of the best known plant phenolic compounds is acetosynngone, which is present in a number of wounded and intact cells of various plants, albeit it in different concentrations However acetosynngone (3,5-dιmethoxy-4-hydroxyacetophenone) is not the only plant phenolic which can induce the expression of vir genes Other examples are α-hydroxy- acetosynngone, sinapimc acid (3 5 dιmethoxy-4-hydroxycιnnamιc acid), synngic acid (4-hydroxy-3,5 dimethoxybenzoic acid) ferulic acid (4-hydroxy-3- methoxycinnamic acid), catechol (1 ,2-dιhydroxybenzene), p-hydroxybenzoic acid (4-hydroxybenzoιc acid) β-resorcylic acid (2 4 dihydroxybenzoic acid), protocatechuic acid (3,4-dιhydroxybenzoιc acid), pyrrogallic acid (2,3,4 - tnhydroxybenzoic acid) , gallic acid (3 4 5-trιhydroxybenzoιc acid) and vanillin (3-methoxy-4-hydroxybenzaldehyde) and these phenolic compounds are known or expected to be able to replace acetosynngone with similar results As used herein, the mentioned molecules are also referred to as plant phenolic compounds Plant phenolic compounds can be used either alone or in combination with other plant phenolics Certain compounds such as osmoprotectants (e g L- proline or betaine), phytohormes, (inter alia NAA), opines or sugars, are expected to act synergistically when added in combination with plant phenolic compounds In a preferred embodiment the invention relates to a method for transforming a cotton plant, i e producing a transge c cotton plant by introduction of a DNA fragment of interest into the genome of the cells of a cotton plant, wherein the method comprises a) cocultivatmg cotton embryogemc callus with Agrobactenum cells, said Agrobactenum cells comprising a DNA fragment of interest operably linked to at least one T-DNA border in the presence of a plant phenolic compound, for a time sufficient to generate embryogemc callus comprising a transformed cotton cell and b) regenerating a transgemc cotton plant from said transformed cell The methods provided by the invention employ cotton embryogemc callus as starting material for the cocultivation with the Agrobactenum cells As used herein "cotton embryogemc callus" or embryogemc callus derived from a cotton expiants" refers to compact or solid callus tissue, cultivated on solid media derived from a cotton explant which can be regenerated into an intact cotton plant through somatic embryogenesis This definition of embryogemc cotton callus does not include embryoge c suspension cells cultured in liquid medium Methods to induce embryogemc callus from a cotton explant have been disclosed in the art, e g in WO 97/12512 It will be clear for the skilled artisan that the source of the cotton explant from which embryogemc callus has been derived is only of limited importance for the method of the current invention Embryogemc callus may be derived from any suitable cotton explant such as but not limited to hypocotyls, cotyledons, immature or mature embryos etc Preferably, the cotton embryogemc callus used in the transformation methods described herein, was obtained by incubation of cotton hypocotyl expiants on hormone free callus induction medium as described in WO 97/12512 "Cocultivation" is used herein to indicate the process of contacting between the embryogemc cotton callus and the Agrobactenum cells, prior to the addition of bacteπostatic or bacteriocidal compounds to inhibit or eliminate the Agrobacteπa The cocultivation stage of an Agrobactenum mediated transformation method thus refers to the time period between the initial contacting of the Agrobacteπa with the plant tissue until the time point where a bacteπostatic or bacteriocidal compound is added to the medium with the intention to remove or inhibit the Agrobactenum strains comprising the DNA fragment of interest "A DNA fragment of interest" is used herein to describe any DNA fragment which one would like to introduce into the genome of cells of a cotton plant, irrespective of whether it encodes a protein or polypeptide, RNA or not Indeed, a DNA fragment may be introduced mainly for tagging purposes The only prerequisite for the DNA fragment of interest is that it should be "operably linked to at least one T-DNA border" As used herein "a T-DNA border' encompasses a DNA fragment comprising an about 25 nucleotide long sequence capable of being recognized by the virulence gene products of an Agrobactenum strain, preferably an A tumefaciens or A rhizogenes strain, and sufficient for transfer of the operably linked DNA to eukaryotic cells, preferably plant cells, particularly sufficient for transfer and integration of the operably linked DNA into the genome of a eukaryotic cell, preferably a plant cell It is clear that this definition encompasses all naturally occurring T-DNA borders from wild-type plasmids, as well as any functional derivative thereof including chemically synthesized T-DNA borders Preferably the DNA of interest is located between two T-DNA borders, preferably on T-DNA vector capable of forming a hybrid Ti-plasmid by single cross-over through a fragment of DNA homology between the T-DNA vector and the helper Ti-plasmid The use of a plant phenolic compound according to the invention increases the transformation efficiency of Agrobactenum mediated DNA transformation of cotton embryogemc callus, and it is expected that this effect is independent of the chromosomal background of the Agrobactenum host, the type of Ti- plasmid, helper-plasmid or T-DNA vector used. Particularly preferred bacterial chromosomal backgrounds are provided by A. tumefaciens C58C1 (Van Larebeke et al , 1974, Nature 252 169-170), A136 (Watson et al., 1975, J. Bacteπol 123. 255-264) or LBA401 1 ( Klapwijk et al., 1980, J. Bacteπol 141 , 128-136). In a preferred embodiment, the Agrobactenum strain used to transform the plant tissue precultured with the plant phenolic compound contains a LL- succinamopme type Ti-plasmid, preferably disarmed such as pEHA101. The method of the invention can also be used in combination with particular Agrobactenum strains, to further increase the transformation efficiency, such as Agrobactenum strains wherein the vir gene expression and/or induction thereof is altered due to the presence of mutant or chimeπc v/rA or virG genes (e.g. Hansen et al., 1994, supra; Chen and Wmans, 1991 , J. Bactenol. 173: 1 139-1 144, Scheeren-Groot et al., 1994, J Bactenol 176' 6418-6246). In another embodiment, Agrobactenum strains comprising an extra virG gene copies, particularly the so-called super virG gene derived from pTiBo542, preferably linked to a multiple-copy plasmid, may be used to further increase the transformation efficiency The concentration of the plant phenolic compound in the cocultivation medium is also believed to have an effect on the transformation efficiency. However, within certain concentration ranges, the effect is minimal The optimal concentration range of plant phenolic compounds in the cocultivation medium may vary depending on the species or variety from which the cotton embryogemc callus is derived, but it is expected that about 100 μM is a suitable concentration for many purposes The optimal concentration may also depend on the nature of the specific plant phenolic compound used, particularly on its cell-division promoting strength It was found for instance that the optimal concentration for acetosynngone is approximately 100 μM, but concentrations as low as approximately 25 μM can be used to obtain a good effect on transformation efficiency Likewise, it is expected that higher concentrations up to approximately 400 μM will yield similar effects Comparable concentrations apply to other plant phenolic compounds, and optimal concentrations can be established easily by experimentation in accordance with this invention Typical co-cultivation times to generate an cotton embryogemc callus comprising transformed cells, are about 3 to about 4 days, but it is expected that a cocultivation time of one day may be sufficient to generate at least some transformed cells Further, it is expected that cocultivation times should not exceed about 7 days It is clear for the skilled artisan that in addition to inclusion of a plant phenolic compound during cocultivation of cotton embryogemc callus with Agrobactenum cells, the used Agrobactenum cells may also be preinduced by incubation with a plant phenolic compound for a time sufficient to induce the virulence genes of the Agrobactenum cells Moreover, it is expected that that preinduction of Agrobactenum cells with a plant phenolic compound for a time sufficient to induce the virulence genes of the Agrobactenum cells, might obviate the requirement for inclusion of a plant phenolic compound during the cocultivation stage Thus, in another preferred embodiment, the invention relates to a method for transforming a cotton plant, i e. producing a transgemc cotton plant by introduction of a DNA fragment of interest into the genome of the cells of a cotton plant, wherein the method comprises : a) incubating an Agrobactenum cell culture comprising a DNA fragment of interest operably linked to at least one T-DNA border, with a plant phenolic compound, for a time sufficient to induce virulence genes of said Agrobactenum cells, b) cocultivating embryogemc cellus derived from a cotton explant with said Agrobactenum cells incubated with said plant phenolic compound, so as to generate embryogemc callus comprising a transformed cotton cell; and c) regenerating a transgemc cotton plant from said transformed cell. Methods to preinduce the virulence genes of Agrobactenum cells by incubation with a plant phenolic compounds, as well as methods to determine whether the virulence genes of an Agrobactenum strain are induced, are available in the art, e.g. as described by Stachel et al., 1985 or Bolton et al., 1986. Optimized methods for induction of Agrobacteπa with plant phenolic compounds, particularly acetosynngone have been described e.g. by Vernade et al., (1988, J. of Bacteriology 170- 5822-5829) incorporated herein by reference. The time of incubation of agrobactenal cells with a plant phenolic compound sufficient to induce the virulence genes may range from a few hours to about two days prior to cocultivation, but typically about 1 day incubation prior to cocultivation will be sufficient Likewise concentration of the plant phenolic compound may range from about 50 μM to about 400 μM, but typically about 100 μM will be a preferred concentration for the plant phenolic compound. After cocultivation, the cotton embryogemc callus is preferably submitted to a selection regime to separate transformed cells from untransformed cells or to at least enrich for transformed cells To this end, the foreign DNA used in the method of this invention preferably also comprises a marker gene, the expression of which allows the separation of transformed cells from non-transformed cells. Such a marker gene generally encodes a protein which allows to phenotypically distinguish transformed cells from untransformed cells In the case of a selectable marker gene, resistance to an antibiotic or other chemical compound that is normally toxic for the cells is generally provided to the cell by expression of that marker gene In plants the selectable marker gene may thus also encode a protein that confers resistance to a herbicide, such as a herbicide comprising a glutamine synthetase inhibitor (e g. phosphinothncin) as an active ingredient. An example of such genes are genes encoding phosphinothncin acetyl transferase such as the sfr or sfry genes (EP 0 242 236, EP 0 242 246; De Block et al , 1987, EMBO J. 6. 2513-2518) However, it can also be that the distinguishable phenotype cannot be selected for, as is the case for marker genes normally referred to a screenable marker genes, including but not limited to, green fluorescent proteins (GFP) or β-glucuromdases (GUS) or β- lactamases well known in the art Moreover, using methods such as PCR-based DNA amplification methods, any DNA sequence, including part of the sequence of the DNA of interest, may be used as a tag for verification of the presence of the DNA fragment of interest. Selection of transformed embryogemc callus cells is preferably performed on solid media, but can also be supplemented or replaced by a selection phase in liquid medium It goes without saying that during the selection and, if required, the regeneration phase, the growth of Agrobactenum has to be inhibited, preferably the Agrobactenum cells have to be eliminated This can be achieved, as well known in the art, by inclusion into the media of an antibiotic, toxic to Agrobacteπa, such as but not limited to cefotaxime Regeneration of the transformed embryogemc callus into transgemc cotton plant lines, can performed according to methods which are well within the skills of the art, such as but not limited to the regeneration methods described In a preferred embodiment, small embryo s are selected for germination and development into mature plants during the regeneration phase, preferably by growing the embryogemc callus in liquid medium on a gyratory shaker, and withholding for germination that fraction of the liquid suspension of embryogemc calli or somatic embryos which pass through a sieve, such as a tea-sieve A transgemc " cotton plant line" as used herein, consists of a group of transgemc cotton plants, originating from one transformed embryogemc callus piece, obtained during the regeneration process In general, plants from one plant line are genetically identical, and originate from one transformation event, thus comprising the same transgenes integrated at the same genomic positions However, individual plants from one plant line can originate from independent transformation events when using /4grabacteπu/77-medιated DNA transfer, and may thus differ from one another When transformation frequencies are expressed by the number of plant lines / 100 initial embryogemc callus pieces, it may be that the actual transformation frequencies (transformation events/ 100 initial callus pieces) are even higher The methods of the invention are particularly suited for the transformation of all cotton plants from which embryogemc callus can be derived (both Gossypium hirsutum and Gossypium barbadense) particularly for Coker 312, Coker310 Coker 5Acala SJ-5, GSC251 10 FiberMax 819 , Siokra 1 -3, T25, GSA75 Acala SJ2 Acala SJ4 Acala SJ5 Acala SJ-C1 Acala B1644, Acala B1654-26 Acala B1654-43 Acala B3991 Acala GC356 Acala GC510, Acala GAM1 , Acala C1 , Acala Royale, Acala Maxxa, Acala Prema, Acala B638, Acala B1810, Acala B2724, Acala B4894, Acala B5002, non Acala "picker" Siokra, "stripper' variety FC2017, Coker 315, STONEVILLE 506, STONEVILLE 825, DP50, DP61 , DP90, DP77, DES1 19, McN235, HBX87, HBX191 , HBX107, FC 3027, CHEMBRED A1 , CHEMBRED A2, CHEMBRED A3, CHEMBRED A4, CHEMBRED B1 , CHEMBRED B2, CHEMBRED B3, CHEMBRED C1 , CHEMBRED C2, CHEMBRED C3, CHEMBRED C4, PAYMASTER 145, HS26, HS46, SICALA PIMA S6 and ORO BLANCO PIMA and plants with genotypes derived thereof The obtained transformed cotton plant can be used in a conventional breeding scheme to produce more transformed cotton plants with the same characteristics or to introduce the DNA fragment of interest into other varieties of the same or related cotton species, and methods further comprising such breeding activities are also included within the scope of the invention. The following Examples describe the methods of the invention in detail Unless stated otherwise in the Examples, all recombinant DNA techniques are carried out according to standard protocols as described in Sambrook et al. (1989) Molecular Cloning A Laboratory Manual, Second Edition, Cold Spπng Harbor Laboratory Press, NY and in Volumes 1 and 2 of Ausubel et al. (1994) Current Protocols in Molecular Biology, Current Protocols, USA Standard materials and methods for plant molecular work are described in Plant Molecular Biology Labfax (1993) by R D D Croy, jointly published by BIOS Scientific Publications Ltd (UK) and Blackwell Scientific Publications, UK. Examples Example 1 : Media, piasmids and bacterial strains used in the Examples 1 1 Media Mm A-qlucose (MAG Agrobactenum growth medium) K 2 HP04.3H 2 0 13.8 g/l H 2 0 KH 2 P0 4 4.5 g/l (NH 4 ) 2 S0 4 1.0 g/l sodium citrate 0.5 g/l MgS0 4 7H 2 0 0.4 g/l thiamine 5.0 g/l glucose 2.0 g/l agar 12.0 g/l AB medium (Aαrobactenum αrowth medium) AB buffer (20x stock) K 2 HP0 4 60 g/l NaH 2 P0 4 H 2 0 22.6 g/l AB salts (20x stock): NH 4 CI 20 g/l MgSO 4 .7H 2 0 6 g/l KCI 3 g/l CaCI 2 .2H 2 0 0.26 g/l FeSO 4 .7H 2 0 50 mg/l 1 liter AB medium contains 50 ml AB buffer, 50 ml AB salts, 5 g/l glucose and 12 g/l agar if appropriate Medium 100 Murashige & Skoog salts+ 30g/l glucose 10 mg/l thiamine 100 mg/l inositol 1 mg/l mcotinic acid 1 mg/l pyπdoxine 0.5 g/l MES buffer pH=5.8 Add 1 .6g/l gelrite and 0.75 g/l MgCI 2 .6H 2 0 whenever solid medium 100 is required Medium 104: Murashige & Skoog salts-t- 30g/l glucose 10 mg/l thiamine 100 mg/l inositol 1 mg/l nicotinic acid 1 mg/l pyridoxine 1 g/l potassium nitrate 0.5 g/l MES buffer pH=5.8 Add 2.0 g/l gelrite and 0.94 g/l MgCI 2 .6H 2 0 whenever solid medium 104 is required Medium 700: Stewards Macro element. KN0 3 0.506g/l NH 4 N0 3 0.240 g/l MgS0 4 .7H 2 0 0.493 g/l CaCl 2 .2H 2 0 0.176 g/l Stewards Micro elements: Kl 0.25 mg/l MnSO 4 .H 2 0 3.84 mg/l ZnS0 4 .7H 2 0 2.59 mg/l Na 2 Mo0 4 .2H 2 0 0.22 mg/l CuS0 4 .5H 2 0 0.0075 mg/l CoCI2.6H20 0.0071 mg/l FeEDTA 0.7 ml/1 of a stock solution containing 0.54 g FeCI 3 .6H 2 0 and 0.74 g Na 2 EDTA in 100 ml H 2 0 Vitamins- thiamine 1 .5 mg/l pyπdoxine 1 .0 mg/l mcotinic acid 0.5 mg/l sucrose: 20 g/l pH=6.8 Solidify the medium with 1 g/l gelrite + 0 47 g/l MgCI 2 6H 2 0 and 2.25 g/i agar Medium 70V Same composition as medium 700 but with 30 g/l glucose solidify the medium with 20 g/l agar Medium 702: Same composition as medium 700 but with 5 g/l sucrose solidify the medium with 1.5 g/l gelrite + 0 71 g/l MgCI 2 .6H 2 0 and 5 g/l agar. 1.2 Piasmids and bacterial strains Agrobactenum tumefaciens strain A331 1 A3311 is A. tumefaciens strain C58C1 Rif R comprising the helper Ti-plasmid pEHA101 (Hood et al. 1986, J. of Bacteriology, 168 1291 -1301 ) and T-DNA vector pTHW136. Plasmid pTHW136 has been descπbed in WO 98/31822. Agrobactenum tumefaciens strain A3784 A3784 is A. tumefaciens strain C58Cl Rιf R comprising the helper Ti-plasmid pEHA101 (Hood ef a/ 1986) and T-DNA vector pTCOI 92 pTCOl 92 is similar to pGSV71 (WO 98/37212) and differs from the latter only in the presence of a region homologous to the nptl gene of pEHA101 , located outside of the T- DNA borders. Agrobactenum tumefaciens strain A3724 A3724 is A tumefaciens strain C58C1 Rιf R comprising the helper Ti-plasmid pEHA101 (Hood et al 1986) and T-DNA vector pTSVH9901 T-DNA vector pTSVH9901 is derived from the T-DNA cloning vector pGSV5 (described in WO 98/31822), compπsing between its border sequences a chimeπc plant expressible bar gene, under control of a CaMV35S promoter and followed by a 3' end formation signal from a nopaline synthase gene. T- DNA vector pTSVH9901 also contains between its border sequences a chimeπc plant expressible Cry9C gene, wherein the CRY9C encoding open reading frame is inserted between a CaMV35S promoter and 3' end region, and wherein a cab22L leader has been inserted in the untranslated mRNA encoding region The T-DNA vector further comprises a region, homologous to the npti gene of pEHA101 , located outside of the T-DNA borders. Agrobactenum tumefaciens strain A3727 A331 1 is A tumefaciens strain C58C1 Rιf R comprising the helper Ti-plasmid pEHA101 (Hood et al. 1986) and T-DNA vector pTSHV0203 T-DNA vector pTSHV0203 is based on the T-DNA cloning vector pGSV5 (WO 98/31822), comprising between its border sequences a chimeπc plant expressible bar gene, under control of a CaMV35S promoter and followed by a 3' end formation signal from a nopaline synthase gene T-DNA vector pTSHV0203 also contains between its border sequences a chimenc plant expressible Cryl Ab gene, wherein the CRYIAb encoding open reading frame is inserted between a CaMV35S promoter and a 3' end region from the octopine synthase gene The T-DNA further comprises a region homologous to the nptl gene of pEHA101 , located outside of the T-DNA borders Example 2: Inclusion of a plant phenolic compound such as acetosyringone during cocultivation allows Agrobactenum mediated transformation of embryogenic cotton callus. Embryogenic cotton callus was obtained in the following way Cotton seeds of variety Coker 312 were disinfected using a 12% sodium hypochloπde solution, and germinated individually in tubes containing a solution of gelrite 2 g/l H 2 0 and 0.94 g/l MgCI 2 .6H 2 0. The tubes were incubated in the dark at 27-28°C After 10 to 14 days, seedlings are collected, the hypocotyls of the seedlings were cut in segments of about 1 cm and incubated on medium 104 (without plant hormones) at 28°C under a regime of 16hr light and 8 hr dark. Every three weeks, the segments were transferred to fresh medium, until embryogenic callus was formed (usually after about 9 weeks) This callus was removed from the expiants and cultured further on medium 104 Agrobactenum strain A 331 1 cells were grown on AB medium or MAG medium, collected and resuspended in M104 liquid medium, pH 5.2 (either with or without 100 μM acetosynngone (AS)) or MAG medium at a density of about 1 x 10 9 CFU/ml. Small embryogenic cotton callus clumps were collected, washed in liquid medium 104 at pH 5.2, and immersed in the Agrobactenum suspension for about 20 minutes. The infected embryogenic calli were than transferred to solid medium 104, pH 5.2, supplemented with either 100 μM AS, 0.5 g/l casamino acids, 100 μM AS and 0.5 g/l casamino acids, or not supplemented at all, and incubated for cocultivation during 4 days in the dark at about 24 °C After the cocultivation phase, the callus clumps were transferred to selective medium 104 supplemented with 50 mg/i kanamycin and 500mg/l Claforan. At different time intervals after the cocultivation, samples of embryogenic callus were collected and subjected to a β-glucuromdase assay, using a chromogemc substrate as described by Jefferson et al. (1987; Plant Mol. Biol. Rep 5. 387-405). The results of these tests are summarized in table I, and are expressed as the percentage of calli expressing GUS-positive spots. As a control, experiments were included using tobacco leaf discs cocultivated with A3311 , using mock-inoculated tobacco leaf discs or using mock- inoculated embryogenic cotton callus. It is clear from the results that inclusion of acetosynngone is required during Agrobactenum mediated transformation of embryogenic callus, both for transient expression and after prolonged cultivation of the transformed calli. Table 1. Overview of results of the effect of different parameters on Agrobactenum mediated transformation of cotton I l\3 00 Example 3: Agrobactenum mediated transformation of cotton using embryogenic callus. Cotton embryogenic callus (EC) was generated as described in Example 2. Clumps of embryogenic callus were collected and washed in liquid medium 104 pH 5.2 Agrobactenum strains A3784, A3724 and A3727 were grown for 3 to 4 days on AB medium pH 7.0, collected and resuspended at a density of approximately 1 to 5 x 109 cells/ml in liquid medium 104, pH 5.2 containing 100 μM acetosynngone. Embryogenic callus clumps were immersed in the Agrobactenum suspension for maximum about 20 minutes, and transferred for cocultivation during 4 days in the dark at 24°C on solid medium 104, p H5.2 supplemented with 100 μM acetosynngone. After this cocultivation, the pieces of callus were transferred to a selective medium 104, pH 5.8, without acetosynngone or plant hormones, supplemented with 500 mg/l Claforan® (to inhibit the development of the Agrobactenum cells) and 5 mg/l phosphinotπcin (PPT) (to select specifically for growth of transgenic calli). Healthy looking pieces of embryogenic callus, actively growing, were transferred every 3 weeks to fresh selective medium 104. Part of the callus (about 200mg) was resuspended in 20 ml liquid medium 100, supplemented with 5 mg/l PPT in a 100 ml flask on a rotary shaker (100-120 rpm) After two weeks culture in the liquid medium, large clumps were removed by passing the suspension through a tea-sieve. The fraction passed-through fraction of embryogenic suspension was left to settle for about 20 mm, after which spent medium was removed and replaced by fresh medium 100. 2 ml of this suspension of small embryo's were plated on solid medium 104, supplemented with 5 mg/l PPT and incubated at 28°C. After about 2 weeks, developing embryos with a size between 4 and 10 mm were transferred to medium 701 and further incubated in the dark at 28 °C . Smaller embryos were transferred to medium 104 overlaid with sterile filter paper (with or without 5 mg/L PPT) to allow increase in size, sufficient for transfer to medium 701. After about 2 weeks, the embryos were transferred to medium 702 (with or without selective pressure) for germination, and incubated at 28 °C, 16 hr light /8 hr dark. Well developed plantlets (which may require 2 to 3 transfers on medium 702) were transferred to small containers containing M700. When these plantlets have developed two to three true leaves they were transferred to bigger containers with medium 700. When the plants were about 10 cm in height, they were transferred to soil under greenhouse conditions. Molecular analyses (Phosphinotricin acetylation assay, Southern hybridization, and ELISA to detect cry gene expression if appropriate) were performed on the callus level. The results of these experiments are summarized in Table 2. Simultaneous Agrobactenum mediated transformation experiments of cotton cotyledons according to the methods known in the art, were performed for comparison. Table 2 Comparison of the results of Agrobactenum mediated transformation experiments using cotton cotyledons or embryogenic callus as starting material NA Not appropriate, ND Not determined * time (expressed in weeks) between the start of the experiment and the determination of the "Plant status" P

Claims: Claims: (77) 1 ) A method for producing a transgenic cotton plant, comprising the step of incubating Agrobactenum ceils comprising a DNA fragment of interest operably linked to at least one T-DNA border with a plant phenolic compound prior to or during the cocultivation of cotton embryogenic callus with said Agrobactenum cells. 2) A method for producing a transgenic cotton plant, said method comprising: a) cocultivating cotton embryogenic callus with Agrobactenum cells, said Agrobactenum cells comprising a DNA fragment of interest operably linked to at least one T-DNA border, in the presence of a plant phenolic compound, for a time sufficient to generate embryogenic callus comprising a transformed cotton cell; and b) regenerating a transgenic cotton plant from said transformed cell. 3) The method of claim 2, wherein said plant phenolic compound is present in a in a concentration range from about 50 μM to about 400 μM. 4) The method of claim 2, wherein said Agrobactenum cells are cocultivated in the presence of said plant phenolic compound for a time period of about 3 to 4 days. 5) The method of claim 2, wherein said embryogenic callus is derived from a hypocotyl of a cotton seedling. 6) The method of claim 2, wherein said plant phenolic compound is selected from the group consisting of acetosynngone, α-hydroxy-acetosyringone, sinapinic acid, syringic acid, ferulic acid, catechol, p-hydroxybenzoic acid, β- resorcylic acid, protocatechuic acid, pyrrogaliic acid, gallic acid and vanillin. SUEPTITUTE SHEET (RULE 26) 7) The method of claim 6, wherein said plant phenolic compound is acetosyringone. 8) The method of claim 2, wherein said Agrobactenum cells are Agrobactenum tumefaciens strain C58C1 (pEHA101), further comprising a DNA fragment of interest. 9) The method of claim 2, further comprising the step of crossing said transgenic cotton plant with another cotton plant. 10) A method for producing a transgenic cotton plant by Agrobacterium-mediated transformation comprising co-cultivating Agrobacterium cells comprising a DNA fragment of interest operably linked to at least one T-DNA border with cotton embryogenic callus, characterized in that said cocultivating occurs in the presence of a plant phenolic compound. 11)Use of a plant phenolic compound for Agrobacterium mediated transformation of cotton embryogenic callus. 12) Use according to claim 10, wherein said plant phenolic compound is acetosyringone. 13) A method for producing a transgenic cotton plant by Agrobacterium-meόiateό transformation characterized in that Agrobacterium cells comprising a DNA fragment of interest operably linked to at least one T-DNA border are cocultivated with cotton embryogenic callus in the presence of a plant phenolic compound.

Inventors: DE SONVILLE ANNE, REYNAERTS ARLETTE, DE SONVILLE, ANNE, REYNAERTS, ARLETTE
Applicants: AVENTIS CROPSCIENCE NV, REYNAERTS ARLETTE, SONVILLE ANNE DE, AVENTIS CROPSCIENCE N.V., DE SONVILLE, ANNE, REYNAERTS, ARLETTE
Application year: 2000
Main classification: C12N15
IPC codes: C12N15