EP1095152A2 - Nucleic acid molecules which code for enzymes derived from wheat and which are involved in the synthesis of starch - Google Patents

Abstract

The invention relates to nucleic acid molecules which code for enzymes and which are involved in the synthesis of starch in plants. These enzymes concern soluble starch synthases derived from wheat. The invention also relates to vectors and host cells which contain the described nucleic acid molecules, especially transformed plant cells and plants which can be regenerated therefrom, which exhibit an increased or reduced activity of the inventive starch synthases.

Description

Nucleic acid molecules encoding wheat enzymes that are involved in starch synthesis

The present invention relates to nucleic acid molecules that encode a wheat enzyme that is involved in starch synthesis in plants. This enzyme is a soluble type I starch synthase.

The invention further relates to vectors, host cells, as well as plant cells and plants, which contain the nucleic acid molecules according to the invention.

Furthermore, processes for the production of transgenic plants are described which synthesize a starch whose properties have been modified due to the introduction of nucleic acid molecules according to the invention.

In view of the increasing importance that vegetable ingredients have recently been given as renewable raw material sources, one of the tasks of biotechnological research is to try to adapt these vegetable raw materials to the requirements of the manufacturing industry. In order to enable the use of renewable raw materials in as many areas as possible, it is also necessary to achieve a wide variety of st offs.

In addition to oils, fats and proteins, polysaccharides are the most important renewable raw materials from plants. A central position among polysaccharides, along with cellulose, is starch, which is one of the most important storage substances in higher plants. Wheat is one of the most important crops, as it produces about 20% of the total starch production in the European Community.

The polysaccharide starch is a polymer made up of chemically uniform building blocks, the glucose molecules. However, it is a very complex mixture of different molecular forms, which differ in the degree of polymerization of the occurrence of branches of the glucose chains and their chain lengths, which can also be derivatized, for example phosphorylated. Starch is therefore not a uniform raw material. A distinction is made in particular between amylose starch, an essentially unbranched polymer composed of 1,4-glycosidically linked glucose molecules, and amylopectin starch, which in turn is a complex mixture of differently branched glucose chains. The branches come about through the occurrence of additional -1, 6-glycosidic linkages. In wheat, about 1 1 to 37% of the synthesized starch consists of amylose starch.

In order to enable the most varied possible use of suitable starches for a wide variety of industrial needs, it is desirable to provide plants which are able to synthesize modified starches which are particularly well suited for various uses. One way to provide such plants is through breeding measures. However, it is very difficult to influence breeding in wheat due to its polyploid character (tetra- and hexaploid). Only recently by crossing naturally occurring mutants has it been possible to produce a "waxy" (amylose-free) wheat (Nakamura et al., Mol. Gen. Genet. 248 (1 995), 253-259).

An alternative to breeding methods is the targeted modification of starch-producing plants using genetic engineering methods. The prerequisite for this, however, is the identification and characterization of the enzymes involved in starch synthesis and / or starch modification, and the isolation of the nucleic acid molecules encoding these enzymes.

The biochemical synthetic pathways that lead to the building of starch are in the essentially known. The starch synthesis in plant cells takes place in the plastids. In photosynthetically active tissues, these are the chloroplasts, in photosynthetically inactive, starch-storing tissues, the amyloplasts.

Important enzymes involved in starch synthase are starch synthases and branching enzymes. Various isoforms are described for starch synthase, all of which catalyze a polymerization reaction by transferring a glucosyl residue from ADP-glucose to α-1,4-glucans. Branching enzymes catalyze the introduction of α-2,6 branches into linear α-1,4-glucans.

Starch synthases can be divided into two classes: starch-bound starch synthases ("granule-bound starch synthases"; GBSS) and soluble starch synthases ("soluble starch synthases"; SSS). This distinction cannot be clearly made in every case, since some of the starch synthases are both bound to starch and in soluble form (Denyer et al., Plant J. 4 (1 993), 1 91-1 98; Mu et al., Plant J. 6 (1,994), 1 51-1 59). For different plant species, different isoforms are described within these classes, which differ in terms of their dependence on starter molecules (so-called "primer dependent" (type II) and "primer independent" (type I) starch synthases).

Only the isoform GBSS I has so far been able to determine the exact function in starch synthesis, in which this enzyme activity is greatly or completely reduced, and synthesize an amylose-free (so-called "waxy") starch (Shure et al., Cell 35 (1,983 ), 225-233; Visser et al., Mol. Gen-Genet. 225 (1 991), 289-296; WO 92/1 1 376), so that this enzyme has been assigned a decisive role in the synthesis of the amylose starch becomes. This phenomenon is also observed in cells of the green algae Chlamydomonas reinhardtii (Delrue et al., J. Bacteriol. 1 74 (1 992), 361 2-3620). at Chlamydomonas could also be shown that GBSS I is not only involved in the synthesis of amylose, but also has an influence on amylopectin synthesis. Mutants lacking GBSS I activity lack a certain fraction of the normally snythetic amylopectin that has longer chain glucans.

The functions of the other isoforms of the starch-bound starch synthases, in particular GBSS II, and the soluble starch synthases have so far been unclear. It is believed that the soluble starch synthases, along with branching enzymes, are involved in the synthesis of the amylopectin (see, for example, Ponstein et al., Plant Physiol. 29 (1 990), 234-241) and that they have an important function in regulating the starch synthesis rate play.

In wheat, at least two isoforms of the starch-bound starch synthase (60 kDA and 100-105 kDA) and another isoform, which may be a soluble starch synthase (Denyer et al., Planta 1 96 (1 995), 256-265; Rahman et al., Aust. J. Plant Physiol. 22 (1 995), 793-803), was identified at the protein level. The presence of several SSS isoforms has previously been demonstrated using chromatographic methods (Rijven, Plant Physiol. 81 (1 986), 448-453). A cDNA encoding GBSS I from wheat has already been described (Ainsworth et al., Plant Mol. Biol. 22 (1 993), 67 to 82).

Nucleic acid sequences which encode starch synthase isoforms from wheat or partial sequences of such nucleic acids have hitherto been known from WO 97/45545.

cDNA sequences coding for starch synthases other than GBSS I have so far only been used for pea (Dry et al., Plant J. 2 (1 992), 1 93-202), rice (Baba et al., Plant Physiol 103 (1 993), 565 to 573) and potato (Edwards et al., Plant J. 8 (1 995), 283 to 294). In addition to wheat, soluble starch synthases have also been identified in a number of other plant species. Soluble starch synthases have been isolated, for example, to homogeneity from pea (Denyer and Smith, Planta 1 86 (1 992), 609 to 61 7) and potato (Edwards et al., Plant J. 8 (1 995), 283 to 294) .

In these cases, it was found that the isoform of the soluble starch synthase identified as SSS III is identical to the starch-bound starch synthase GBSS II (Denyer et al., Plant J. 4 (1 993), 1 91 to 1 98; Edwards et al., Plant J. 8 (1,995), 283-294). For several other plant species, the presence of several SSS isoforms has been described using chromatographic methods, for example in the case of barley (Tyynelä and Schulman, Physiologica Plantarum 89 (1 993) 835-841; Kreis, Planta 148 (1 980), 41 2 to 41 6 ). However, DNA sequences encoding these proteins have not been described.

In order to provide further possibilities for modifying any starch-storing plants, preferably cereals, in particular wheat, in such a way that they synthesize a modified starch, it is necessary in each case to identify DNA sequences which code further isoforms of the starch synthases.

The present invention is therefore based on the object of making available nucleic acid molecules, in particular those from wheat, which encode enzymes involved in starch biosynthesis and with the aid of which it is possible to produce genetically modified plants which are suitable for the production of chemical and / or or physical properties of modified vegetable starches.

This task is accomplished by the provision of the claims designated embodiments solved.

The present invention therefore relates to nucleic acid molecules which proteins with the activity of a soluble starch synthase from wheat, wherein such molecules preferably encode proteins which essentially have the Seq ID no. Include 2 given amino acid sequence. In particular, the invention relates to nucleic acid molecules which are listed under Seq ID No. 1 or a part thereof, preferably molecules which contain the nucleotide sequence specified in Seq ID No. 1 indicated coding region comprise, particularly preferably nucleotide No. 9 to 570 of Seq ID No. 1 as well as corresponding ribonucleotide sequences.

The present invention further relates to nucleic acid molecules which hybridized with one of the nucleic acid molecules according to the invention.

The invention also relates to nucleic acid molecules which encode a soluble starch synthase from wheat and whose sequence deviates from the nucleotide sequences of the molecules described above due to the degeneration of the genetic code.

The invention also relates to nucleic acid molecules which have a sequence which is complementary to all or part of one of the abovementioned sequences.

In the context of this invention, the term “hybridization” means hybridization under conventional hybridization conditions, preferably under stringent conditions, as described, for example, in Sambrook et al., Molecular Cloning, A Laboratory Manual, 2nd edition (1,989) Cold Spring Harbor Laboratory Press , Cold Spring Harbor, NY). Hybridization is particularly preferably carried out under the following

Conditions:

Hybridization buffer: 2 x SSC; 1 0 x Denhardt's solution (Fikoll 400 + PEG +

BSA; Ratio 1: 1: 1); 0.1% SDS; 5mM EDTA;

50 mM Na ₂ HPO ₄ ; 250 µg / ml herring sperm DNA;

50 µg / ml tRNA; or

0.25 M sodium phosphate buffer pH 7.2;

1mM EDTA; 7% SDS hybridization temperature T = 65 to 70 ° C

Wash buffer: 0.2 x SSC; 0.1% SDS

Washing temperature T = 40 to 75 ° C.

In principle, nucleic acid molecules which hybridize with the nucleic acid molecules according to the invention can encode starch synthases from any wheat plant which expresses such proteins.

Nucleic acid molecules that hybridize with the molecules of the invention can e.g. isolated from genomic or from cDNA libraries of wheat or wheat plant tissue. Alternatively, they can be produced by genetic engineering methods or by chemical synthesis.

Such nucleic acid molecules can be identified and isolated using the molecules according to the invention or parts of these molecules or the reverse complements of these molecules, e.g. by means of hybridization according to standard methods (see e.g. Sambrook et al., 1 989, Molecular Cloning, A Laboratory Manual, 2nd edition Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY).

For example, nucleic acid molecules can be used as the hybridization sample that exactly or essentially the ones under Seq ID No. 1 indicated nucleotide sequence or parts of this sequence. With the as The fragments used for the hybridization sample can also be synthetic fragments which were produced with the aid of the usual synthetic techniques and whose sequence essentially corresponds to that of a nucleic acid molecule according to the invention.

The molecules hybridizing with the nucleic acid molecules according to the invention also include fragments, derivatives and allelic variants of the nucleic acid molecules described above, which encode a starch synthase according to the invention from wheat. Fragments are understood to mean parts of the nucleic acid molecules that are long enough to encode one of the proteins described. The term derivative in this context means that the sequences of these molecules differ from the sequences of the nucleic acid molecules described above at one or more positions and have a high degree of homology to these sequences. Homology means a sequence identity of at least 40%, in particular an identity of at least 60%, preferably over 80% and particularly preferably over 90%. The deviations from the nucleic acid molecules described above may have resulted from deletion, substitution, insertion or recombination.

Homology also means that there is functional and / or structural equivalence between the nucleic acid molecules in question or the proteins encoded by them. The nucleic acid molecules which are homologous to the molecules described above and which are derivatives of these molecules are usually variations of these molecules which are modifications which have the same biological function. These can be both naturally occurring variations, for example sequences from other organisms, or mutations, wherein these mutations can have occurred naturally or have been introduced by targeted mutagenesis. Furthermore, the variations can be act synthetically produced sequences. The allelic variants can be both naturally occurring variants and also synthetically produced variants or those produced by recombinant DNA techniques.

The proteins encoded by the different variants of the nucleic acid molecules according to the invention have certain common characteristics. For this, e.g. Enzyme activity, molecular weight, immunological reactivity, conformation etc. belong as well as physical properties such as the running behavior in gel electrophoresis, chromatographic behavior, sedimentation coefficient, solubility, spectroscopic properties, charge properties, stability; pH optimum, temperature optimum etc.

Important characteristics of a starch synthase are: i) its localization in the stroma of plastids in plant cells; ii) their ability to synthesize linear - 1, 4-linked polyglucans. This activity can be determined as described in Denyer and Smith (Plante 1 86 (1 992), 606 to 61 7). The protein encoded by the nucleic acid molecules according to the invention is a soluble type I starch synthase from wheat. These proteins have certain areas of homology with previously known soluble starch synthases from other plant species.

The nucleic acid molecules according to the invention can be DNA molecules, in particular cDNA or genomic molecules. Furthermore, the nucleic acid molecules according to the invention can be RNA molecules, which can result, for example, from transcription of a nucleic acid molecule according to the invention. The nucleic acid molecules according to the invention can, for. B. obtained from natural sources or produced by recombinant techniques or synthetically. The invention also relates to oligonucleotides which hybridize specifically with a nucleic acid molecule according to the invention. Such oligonucleotides preferably have a length of at least 10, in particular at least 15 and particularly preferably at least 50 nucleotides. The oligonucleotides according to the invention are characterized in that they hybridize specifically with nucleic acid molecules according to the invention, ie not or only to a very small extent with nucleic acid sequences which code for other proteins, in particular other starch synthases. The oligonucleotides according to the invention can be used, for example, as primers for a PCR reaction or as a hybridization sample for the isolation of related genes. They can also be components of antisense constructs or of DNA molecules which code for suitable ribozymes.

The invention further relates to vectors, in particular plasmids, cosmids, phagemids, viruses, bacteriophages and other vectors which are common in genetic engineering and which contain the nucleic acid molecules according to the invention described above. Such vectors are suitable for the transformation of pro- or eukaryotic, preferably plant cells.

The vectors particularly preferably allow the nucleic acid molecules according to the invention, optionally together with flanking regulatory regions, to be integrated into the genome of the plant cell. Examples of this are binary vectors which can be used in gene transfer mediated by agrobacteria. The integration of a nucleic acid molecule according to the invention in sense or anti-sense orientation preferably ensures the synthesis of a translatable or optionally non-translatable RNA in the transformed pro- or eukaryotic cells.

The term "vector" generally designates a suitable, the expert Known tool that enables the targeted transfer of a single- or double-stranded nucleic acid molecule into a host cell, for example a DNA or RNA virus, a virus fragment, a plasmid construct, which, in the presence or absence of regulatory elements, may be suitable for nucleic acid transfer in cells can, carrier materials such as glass fiber or metal particles such as can be used for example in the "particle gun" process, but it can also include a nucleic acid molecule that can be brought directly into a cell by chemical or physical methods.

In a preferred embodiment, the nucleic acid molecules contained in the vectors are linked to regulatory elements which ensure the transcription and synthesis of a translatable RNA in pro- or eukaryotic cells or, if desired, the synthesis of a non-translatable RNA.

The expression of the nucleic acid molecules according to the invention in prokaryotic cells, for example in Escherichia coli, is important for a more precise characterization of the enzymatic activities of the enzymes for which these molecules code. In particular, it is possible to characterize the product which is synthesized by the corresponding enzymes in the absence of other enzymes which are involved in the starch synthesis in the plant cell. This allows conclusions to be drawn about the function that the corresponding protein performs in the starch synthesis in the plant cell.

In addition, it is possible using conventional molecular biological techniques (see, for example, Sambrook et al., 1,989, Molecular Cloning, A Laboratory Manual, 2nd ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY) to make various mutations in the nucleic acid molecules according to the invention introduce, which leads to the synthesis of proteins with possibly changed biological properties. The first is the generation of Deletion mutants possible, in which progressive deletions from the 5 'or from the 3' end of the coding DNA sequence generate nucleic acid molecules which lead to the synthesis of correspondingly shortened proteins. Such deletions at the 5 'end of the nucleotide sequence make it possible, for example, to identify amino acid sequences which are responsible for the translocation of the enzyme into the plastids (transit peptides). This allows targeted production of enzymes that are no longer localized in the plastids but in the cytosol by removing the corresponding sequences, or are localized in other compartments due to the addition of other signal sequences.

On the other hand, the introduction of point mutations is also conceivable at positions in which a change in the amino acid sequence has an influence, for example on the enzyme activity or the regulation of the enzyme. In this way, for example, mutants can be produced which have a changed K _m value or which are no longer subject to the regulatory mechanisms normally present in the cell via allosteric regulation or covalent modification.

Furthermore, mutants can be produced which have a modified substrate or product specificity of the protein according to the invention, for example by using ADP-glucose-6-phosphate instead of ADP-glucose. Furthermore, mutants can be produced which have a changed activity-temperature profile of the protein according to the invention.

For the genetic modification of prokaryotic cells, the nucleic acid molecules according to the invention or parts of these molecules can be introduced into plasmids which permit mutagenesis or a sequence change by recombination of DNA sequences. With the help of standard methods (cf. Sambrook et al., 1 989, Molecular Cloning: A laboratory manual, 2nd ed., Cold Spring Harbor Laboratory Press, NY, USA), base changes can be made or natural or synthetic sequences added. To connect the DNA fragments to one another, adapters or linkers can be attached to the fragments. Manipulations which provide suitable restriction sites or which remove superfluous DNA or restriction sites can also be used. Where insertions, deletions or substitutions are possible, in vitro mutagenesis, "primer repair", restriction or ligation can be used. Sequence analysis, restriction analysis or other biochemical-molecular biological methods are generally used as the analysis method.

In a further embodiment, the invention relates to host cells, in particular pro- or eukaryotic cells which are transformed with a nucleic acid molecule according to the invention or a vector according to the invention described above, and cells which are derived from cells transformed in this way and contain a nucleic acid molecule according to the invention or a vector. These are preferably pro- or eukaryotic, in particular plant cells.

The invention further relates to recombinantly producible proteins with the activity of a starch synthase, which are encoded by the nucleic acid molecules according to the invention, and methods for their production, in which a host cell according to the invention is cultivated under suitable conditions known to the person skilled in the art, which allow the synthesis of the protein according to the invention, and then it from the

Host cells and / or the culture medium is isolated.

By providing the nucleic acid molecules according to the invention, it is now possible to use genetic engineering methods to specifically intervene in the starch metabolism of plants and to change it in such a way that a modified starch is synthesized, which in its physico-chemical form Properties, for example the amylose / amylopectin ratio, the degree of branching, the average chain length, the phosphate content, the gelatinization behavior, the gel or film formation properties, the starch grain size and / or the starch grain shape is changed compared to known starch.

It is thus possible to express the nucleic acid molecules according to the invention in plant cells in order to increase the activity of the corresponding starch synthase, or to introduce them into cells which naturally do not express this enzyme. Furthermore, it is possible to modify the nucleic acid molecules according to the invention by methods known to the person skilled in the art in order to obtain starch synthases according to the invention which are no longer subject to the natural cellular regulation mechanisms or which have changed temperature-activity profiles or substrate or product specificities.

When the nucleic acid molecules according to the invention are expressed in plants, there is in principle the possibility that the synthesized protein can be localized in any compartment of the plant cell. In order to achieve localization in a particular compartment, the sequence ensuring localization in plastids must be deleted and the remaining coding region may have to be linked to DNA sequences which ensure localization in the respective compartment. Such sequences are known (see for example Braun et al., EMBO J. 1 1 (1 992), 321 9-3227; Wolter et al., Proc. Natl. Acad. Sci. USA 85 (1 988), 846-850 ; Sonnewald et al., Plant J. 1 (1,991), 95-106).

The present invention thus also relates to a method for producing transgenic plant cells which are transformed with a nucleic acid molecule or vector according to the invention, in which a nucleic acid molecule according to the invention or a vector according to the invention in the genome of a plant cell is integrated, the transgenic plant cells which were transformed by means of a nucleic acid molecule or vector according to the invention and transgenic plant cells which are derived from cells transformed in this way. The cells according to the invention contain one or more nucleic acid molecules or vectors according to the invention, these being preferably linked to regulatory DNA elements which ensure transcription in plant cells, in particular with a suitable promoter. Such cells can be distinguished from naturally occurring plant cells, inter alia, in that they contain a nucleic acid molecule according to the invention which does not naturally occur in these cells or in that such a molecule is integrated at a location in the genome of the cell where it does not otherwise occur , ie in a different genomic environment. Furthermore, such transgenic plant cells according to the invention can be distinguished from naturally occurring plant cells in that they contain at least one copy of a nucleic acid molecule according to the invention stably integrated into their genome, optionally in addition to copies of such a molecule that occur naturally in the cells. If the nucleic acid molecule (s) introduced into the cells are additional copies of molecules already naturally occurring in the cells, the plant cells according to the invention can be distinguished from naturally occurring cells in particular in that these additional copy (s) ) is localized in locations in the genome where it does not naturally occur. This can be easily checked, for example, with the aid of a Southern blot analysis according to methods known to the person skilled in the art.

If the nucleic acid molecule according to the invention introduced into the plant genome is heterologous with respect to the plant cell, then the transgenic plant cells have transcripts of the nucleic acid molecules according to the invention, which are e.g. B. simply by Northern blot analysis according to methods known to those skilled in the art. If the introduced nucleic acid molecule according to the invention is homologous with respect to the plant cell, the cells according to the invention can be distinguished from naturally occurring cells, for example on the basis of the additional expression of nucleic acid molecules according to the invention. The transgenic plant cells preferably contain more transcripts of the nucleic acid molecules according to the invention. This can e.g. B. can be detected by Northern blot analysis. "More" preferably means at least 10% more, preferably at least 20% more and particularly preferably at least 50% more transcripts than corresponding, non-transformed cells. The cells preferably also have a corresponding (at least 10%, 20% or 50%) increase in activity or, if appropriate, a reduction in activity of the protein according to the invention. The transgenic plant cells can be regenerated into whole plants using techniques known to those skilled in the art.

The present invention also relates to a method for producing transgenic plants, in which one or more nucleic acid molecules or vectors according to the invention are integrated into the genome of a plant cell and a complete plant is regenerated from said plant cell. The plants obtainable by regeneration of the transgenic plant cells according to the invention are also the subject of the present invention. The invention furthermore relates to plants which contain the transgenic plant cells described above. The transgenic plants can in principle be plants of any plant species, ie both monocot and dicot plants. They are preferably useful plants, preferably starch-synthesizing or starch-storing plants, particularly preferably rye, barley, oats, wheat, millet, sago, maize, rice, pea, pea, cassava, potato, tomato, rapeseed, soybean, hemp, flax, sunflower , Cow pea or arrowroot, especially wheat, corn, rice and potato. The invention also relates to propagation material of the plants according to the invention, for example fruits, seeds, tubers, rhizomes, seedlings, cuttings, calli, protoplasts, cell cultures etc.

The present invention further relates to a method for producing a modified starch comprising the step of extracting the starch from a plant according to the invention described above and / or from starch-storing parts of such a plant.

Methods for extracting the starch from plants or from starch-storing parts of plants, in particular from wheat, are known to the person skilled in the art, cf. e.g. Eckhoff et al. (Cereal Chem. 73 (1 996) 54-57) "Starch: Chemistry and Technology (Ed .: Whistler, BeMiller and Paschall (1 994), 2nd edition, Academic Press Inc. London Ltd; ISBN 0-1 2- 746270-8; see e.g. Chapter XII, page 41 2-468: Maize and sorghum starches: manufacture; by Watson; Chapter XIII, pages 469-479: tapioca, arrowroot and sago starches: manufacture; by Corbishley and Miller; Chapter XIV, pages 479-490: Potato Starch: Manufacture and Uses; by Mitch; Chapter XV, Pages 491 to 506: Wheat Starch: Manufacture, Modification and Uses; by Knight and Oson; and Chapter XVI, Pages 507 to 528: Rice Starch : Manufacture and Uses; by Rohmer and Klem) Devices commonly used in processes for extracting starch from plant material are separators, decanters, hydrocyclones, spray dryers and fluidized bed dryers.

Based on the expression of a nucleic acid molecule according to the invention, the transgenic plant cells and plants according to the invention synthesize a starch which has its physicochemical properties, for example the amylose / amylopectin ratio, the degree of branching, the average chain length, the phosphate content, the gelatinization behavior, the starch grain size and / or the starch grain shape compared to wild type Plants synthesized starch is changed. In particular, such a starch can be changed with regard to the viscosity and / or the film or gel formation properties of pastes of this starch compared to known starches.

The present invention furthermore relates to a starch which can be obtained from the plant cells, plants and their propagation material according to the invention and starch which can be obtained by the process according to the invention described above.

It is also possible to use the nucleic acid molecules according to the invention to produce plant cells and plants in which the activity of a protein according to the invention is reduced. This also leads to the synthesis of a starch with changed chemical and / or physical properties compared to starch from wild-type plant cells.

Another object of the invention is thus also a transgenic plant cell containing a nucleic acid molecule according to the invention, in which the activity of a starch synthase is reduced compared to a non-transformed cell.

The production of plant cells with a reduced activity of a starch synthase can be achieved, for example, by the expression of a corresponding antisense-RNA, a sense-RNA to achieve a cosuppression effect or the expression of a correspondingly constructed ribozyme which specifically cleaves transcripts which code for a starch synthase , using the nucleic acid molecules according to the invention by methods known to the person skilled in the art, cf. Jorgensen (Trends Biotechnol. 8 (1 990), 340-344), Niebel et al., (Curr. Top. Microbiol. Immunol. 1 97 (1 995), 91-103), Flavell et al. (Curr. Top. Microbiol. Immunol. 197 (1995), 43-46), Palaqui and Vaucheret (Plant. Mol. Biol. 29 (1 995), 149-1 59), Vaucheret et al., (Mol. Gen. Genet. 248 (1 995), 31 1 -31 7), de Borne et al. (Mol. Gen. Genet. 243 (1,994), 61 3-621).

Preferably, to reduce the activity of a starch synthase according to the invention in the plant cells, the number of transcripts encoding it is reduced, e.g. by expression of an antisense RNA.

For this purpose, a DNA molecule can be used which comprises the entire sequence coding for a protein according to the invention including any flanking sequences which may be present, and also DNA molecules which only comprise parts of the coding sequence, these parts having to be long enough to to cause an antisense effect in the cells. In general, sequences up to a minimum length of 15 bp, preferably a length of 100-500 bp, can be used for efficient antisense inhibition, in particular sequences with a length of more than 500 bp. As a rule, DNA molecules are used that are shorter than 5000 bp, preferably sequences that are shorter than 2500 bp.

It is also possible to use DNA sequences which have a high degree of homology to the sequences of the DNA molecules according to the invention, but which are not completely identical. The minimum homology should be greater than approximately 65%. The use of sequences with homologies between 95 and 100% is preferred.

The invention also relates to a method for producing a modified starch, comprising the step of extracting the starch from a cell or plant according to the invention and / or from starch-storing parts of such a plant.

The invention furthermore relates to starch which can be obtained from the cells, plants and propagation material or parts thereof according to the invention and starch which can be obtained by a process according to the invention.

The starches according to the invention can be modified by processes known to those skilled in the art and are suitable in unmodified or modified form for various uses in the food or non-food sector.

Basically, the possible uses of the starches according to the invention can be divided into two large areas. One area comprises the hydrolysis products of starch, mainly glucose and glucan building blocks, which are obtained via enzymatic or chemical processes. They serve as the starting material for further chemical modifications and processes, such as fermentation. The simplicity and cost-effective execution of a hydrolysis process can be important for reducing the costs. Currently, it is essentially enzymatic using amyloglucosidase. It would be conceivable to save costs by using fewer enzymes. A structural change in strength, e.g. Surface enlargement of the grain, easier digestibility through e.g. A lower degree of branching or a steric structure that limits the accessibility for the enzymes used could cause this.

The other area, in which the starches according to the invention are used as so-called native starches because of their polymer structure, is divided into two further areas of application:

1 . Food industry

Starch is a classic additive for many foods, where it essentially takes on the function of binding aqueous additives or increases the viscosity or increases gel formation. The important properties are the flow and Sorption behavior, the swelling and gelatinization temperature, the viscosity and thickening performance, the solubility of the starch, the transparency and paste structure, the heat, shear and acid stability, the tendency to retrogradation, the ability to form films, the freeze / thaw stability, the viscosity stability in Salt solutions, digestibility and the ability to form complexes with, for example, inorganic or organic ions.

2. Non-food industry

In this large area, starch can be used as an additive for different manufacturing processes or as an additive in technical products. When using starch as an auxiliary, the paper and cardboard industry should be mentioned in particular. The starch primarily serves for retardation (retention of solids), the setting of filler and fine particles, as a strengthening agent and for drainage. In addition, the favorable properties of the starch in terms of rigidity, hardness, sound, grip, gloss, smoothness, splitting resistance and surfaces are exploited.

2.1 Paper and cardboard industry

There are four areas of application within the paper manufacturing process, namely surface, line, mass and spraying. The requirements for the starch in relation to the surface treatment are essentially a high degree of whiteness, an adapted viscosity, high viscosity stability, good film formation and low dust formation. When used in the coating, the solids content, an adapted viscosity, a high binding capacity and high pigment affinity play an important role. As an addition to the mass, rapid, even, loss-free distribution, high mechanical stability and complete restraint in the paper flow are important. At the Use of the starch in the spray area is also of importance to an adapted solids content, high viscosity and high binding capacity.

2.2 Adhesives industry

A large area of use of the starches is in the adhesive industry, where the possible uses are divided into four areas: use as pure starch glue, use with starch glues prepared with special chemicals, use of starch as an additive to synthetic resins and polymer dispersions, and use of starches as an extender for synthetic adhesives. 90% of the starch-based adhesives are used in the fields of corrugated cardboard, paper bags, bags and pouches, composite materials for paper and aluminum, cardboard packaging and rewetting glue for envelopes, stamps, etc.

2.3 Textile and textile care products industry

A large field of application for the starches as an auxiliary and additive is the area of manufacture of textiles and textile care products. The following four areas of application can be distinguished within the textile industry: The use of starch as a sizing agent, i.e. as an auxiliary for smoothing and strengthening the hook-and-loop behavior to protect against the tensile forces that occur during weaving and to increase the abrasion resistance during weaving, starch as a means of textile upgrading after poor-quality pre-treatments such as bleaching, dyeing, etc., starch as a thickening agent in the manufacture of color pastes to prevent dye diffusion and starch as an additive to chaining agents for sewing threads. 2.4 Building materials industry

The fourth area of application is the use of starches as an additive in building materials. One example is the production of gypsum plasterboard, in which the starch mixed in the gypsum slurry pastes with the water, diffuses to the surface of the gypsum board and binds the cardboard to the board there. Other areas of application are admixing to plaster and mineral fibers. In ready-mixed concrete, starch products are used to delay setting.

2.5 Soil stabilization

Another market for starch is in the manufacture of soil stabilizers that are used to temporarily protect soil particles from water during artificial earthmoving. Combined products made of starch and polymer emulsions are, according to current knowledge, to be equated with the previously used products in terms of their erosion and incrustation-reducing effects, but are significantly less expensive than these.

2.6 Use in crop protection and fertilizers

One area of application is the use of starch in crop protection agents to change the specific properties of the preparations. The starch can be used to improve the wetting of crop protection agents and fertilizers, to release the active ingredients in a dosed manner, to convert liquid, volatile and / or malodorous active ingredients into microcrystalline, stable, moldable substances, to mix incompatible compounds and to extend the duration of action by reducing the Decomposition can be used.

2.7 Pharmaceuticals, medicine and cosmetics industry

Another area of application is in the pharmaceutical, medical and cosmetic industries. In the pharmaceutical industry, starch can be considered Binder for tablets or for binder dilution in capsules can be used. The starch can furthermore serve as a tablet disintegrant, since after swallowing it absorbs liquid and swells to such an extent after a short time that the active substance is released. Medical lubricant and wound powders are based on starch for qualitative reasons. In the field of cosmetics, starches are used, for example, as carriers for powder additives such as fragrances and salicylic acid. A relatively large area of application for starch is toothpaste.

2.8 Starch addition to coals and briquettes

Starch is used as an additive to coal and briquette. Coal can be agglomerated or briquetted with a high-quality addition of starch, which prevents the briquettes from breaking down prematurely. The added starch is between 4 and 6% for barbecued coal and between 0, 1 and 0.5% for calorized coal. Furthermore, starches are becoming increasingly important as binders, since their addition to coal and briquette can significantly reduce the emissions of harmful substances.

2.9 Ore and coal sludge processing

The starch can also be used as a flocculant in ore and coal sludge processing.

2.10 Foundry auxiliary

Another area of application is as an additive to foundry additives. Various casting processes require cores that are made from binder-mixed sands. Bentonite, which is mixed with modified starches, mostly swelling starches, is predominantly used today as a binder.

The purpose of the starch addition is to increase the flow resistance and to improve the binding strength. In addition, the source strengths have other production-related requirements, such as dispersibility in cold water, rehydration, good miscibility in sand and high water retention.

2.1 1 Use in the rubber industry

In the rubber industry, the starch can be used to improve the technical and optical quality. The reasons for this are the improvement of the surface gloss, the improvement of the handle and the appearance, for this reason starch is sprinkled on the sticky rubberized surfaces of rubber materials before the cold vulcanization, and the improvement of the printability of the rubber.

2.1 2 Manufacture of leather substitutes

Another way of selling the modified starches is in the production of leather substitutes.

2.13 Starch in synthetic polymers

The following areas of application are emerging in the plastics sector: the integration of starch secondary products in the processing process (starch is only a filler, there is no direct link between synthetic polymer and starch) or, alternatively, the integration of starch secondary products in the production of polymers (starch and polymer are one firm bond).

The use of starch as a pure filler is not competitive compared to other substances such as talc. It is different if the specific starch properties come into play and this significantly changes the property profile of the end products. An example of this is the use of starch products in the processing of thermoplastics, such as polyethylene. The starch and the synthetic polymer are co-expressed in a 1: 1 ratio to form a 'master batch' combined, from which various products are made with granulated polyethylene using conventional processing techniques. By incorporating starch in polyethylene films, an increased material permeability for hollow bodies, an improved water vapor permeability, an improved antistatic behavior, an improved antiblocking behavior and improved printability with aqueous inks can be achieved.

Another option is to use the starch in polyurethane foams. By adapting the starch derivatives and by optimizing the process, it is possible to control the reaction between synthetic polymers and the hydroxyl groups of the starches. The result is polyurethane foils that get the following property profiles through the use of starch: a reduction in the coefficient of thermal expansion, a reduction in shrinkage behavior, an improvement in pressure / stress behavior, an increase in water vapor permeability without changing the water absorption, a reduction in flammability and tear density, no dripping of flammable parts, Halogen free and reduced aging. Disadvantages that are currently still present are reduced compressive strength and reduced impact resistance.

Product development is no longer limited to foils. Solid plastic products such as pots, plates and bowls can also be manufactured with a starch content of over 50%. Furthermore, starch / polymer mixtures can be assessed favorably because they have a much higher biodegradability.

Because of their extreme water-binding capacity, starch graft polymers have also become extremely important. these are Products with a backbone made of starch and a side grid of a synthetic monomer grafted on according to the principle of the radical chain mechanism. The starch graft polymers available today are characterized by better binding and retention properties of up to 1000 g of water per g of starch with high viscosity. The areas of application for these superabsorbents have expanded considerably in recent years and are in the hygiene sector with products such as diapers and pads as well as in the agricultural sector, for example in seed pilling.

Decisive for the use of the new, genetically modified starches are on the one hand the structure, water content, protein content, lipid content, fiber content, ash / phosphate content, amylose / amylopectin ratio, molar mass distribution, degree of branching, grain size and shape as well as crystallinity, and on the other hand also the properties flow into the following characteristics: flow and sorption behavior, gelatinization temperature, viscosity, viscosity stability in salt solutions, thickening performance, solubility, paste structure and transparency, heat, shear and acid stability, tendency to retrogradation, gel formation, freeze / thaw stability, complex formation, iodine binding, film formation, adhesive strength , Enzyme stability, digestibility and reactivity.

The generation of modified starches by means of genetic engineering methods can, on the one hand, change the properties of the starch obtained from the plant in such a way that further modifications by means of chemical or physical methods no longer appear necessary. On the other hand, the starches modified by genetic engineering processes can be subjected to further chemical modifications, which leads to further improvements in quality for certain of the fields of application described above. These chemical modifications are generally known. In particular, these are modifications by heat treatment, treatment with organic or inorganic acids, oxidation and esterifications, which, for example, lead to the formation of phosphate, nitrate, sulfate, xanthate, acetate and Lead citrate starches. Furthermore, monohydric or polyhydric alcohols can be used in the presence of strong acids to produce starch ethers, so that starch alkyl ether, O-allyl ether, hydroxyl alkyl ether, O-carboxylmethyl ether, N-containing starch ether, P-containing starch ether), S-containing starch ether, cross-linked starches or starch graft polymers result.

A preferred use of the starches according to the invention is in the production of packaging material and disposable articles on the one hand and as food or intermediate food product on the other hand.

To express the nucleic acid molecules according to the invention in sense or antisense orientation in plant cells, these are linked to regulatory DNA elements which ensure transcription in plant cells. These include in particular promoters, enhancers and terminators. In general, any promoter active in plant cells can be used for the expression.

The promoter can be selected so that the expression is constitutive or only in a certain tissue, at a certain time in plant development or at a time determined by external influences. The promoter can be homologous or heterologous to the plant. Suitable promoters are, for example, the 35S RNA promoter of the Cauliflower Mosaic Virus and the ubiquitin promoter from maize for constitutive expression, the patatin promoter B33 (Rocha-Sosa et al., EMBO J. 8 (1 989), 23-29 ) for a tuber-specific expression or a promoter which ensures expression only in photosynthetically active tissues, for example the ST-LS1 promoter (Stockhaus et al., Proc. Natl. Acad. Sci. USA 84 (1 987), 7943-7947 ; Stockhaus et al., EMBO J. 8 (1 989), 2445-2451) or, for an endosperm-specific expression, the HMG promoter from wheat, the USP promoter, the phaseolin promoter or promoters from zein genes from maize . There may also be a termination sequence which serves to correctly terminate the transcription and to add a Poiy-A tail to the transcript, which is assigned a function in stabilizing the transcripts. Such elements are described in the literature (cf. Gielen et al., EMBO J. 8 (1 989), 23-29) and are interchangeable.

The present invention provides nucleic acid molecules that encode a protein with the function of a soluble starch synthase from wheat. The nucleic acid molecules according to the invention allow the production of this enzyme, its functional identification within the starch biosynthesis, the production of genetically modified plants in which the activity of this enzyme is changed and thus enables the synthesis of a starch with a modified structure and changed physicochemical properties in such modified plants .

In principle, the nucleic acid molecules according to the invention can also be used to produce plants in which the activity of the starch synthase according to the invention is increased or decreased and at the same time the activities of other enzymes involved in starch synthesis are changed. The change in the activities of a starch synthase in plants leads to the synthesis of a starch with a different structure. Furthermore, nucleic acid molecules which encode a starch synthase or corresponding antisense constructs can be introduced into plant cells in which the synthesis of endogenous GBSS I, SSS or GBSS II proteins is already inhibited due to an antisense effect or a mutation or the synthesis of the Branching enzyme is inhibited (such as in WO 92/14827 or Shannon and Garwood, 1,984, in Whistler, BeMiller and Paschall, Starch: Chemistry and Technology, Academic Press, London, 2nd Edition: 25-86).

Is the inhibition of the synthesis of several involved in the starch biosynthesis Enzymes are achieved in transformed plants, DNA molecules can be used for the transformation which simultaneously contain several regions coding for the corresponding enzymes in antisense orientation under the control of a suitable promoter. Alternatively, each sequence can be under the control of its own promoter, or the sequences can be transcribed as a fusion from a common promoter or under the control of a common promoter. The latter alternative will generally be preferable since in this case the synthesis of the corresponding proteins should be inhibited to approximately the same extent. For the length of the individual coding regions which are used in such a construct, that which has already been stated above for the production of antisense constructs applies. In principle, there is no upper limit for the number of antisense fragments transcribed from a promoter in such a DNA molecule. However, the resulting transcript should preferably not exceed a length of 10 kb and in particular a length of 5 kb.

Coding regions, which are located in such DNA molecules in combination with other coding regions in antisense orientation behind a suitable promoter, can originate from DNA sequences which code for the following proteins: starch-bound (GBSS I and II) and soluble Starch synthases (SSS I and II), branching enzymes (isoamylases, pullulanases, R enzymes, "branching" enzymes, "debranching" enzymes), starch phosphorylases and disproportionation enzymes. This is only an example. The use of other DNA sequences in the context of such a combination is also conceivable.

With the help of such constructs, it is possible to inhibit the synthesis of several enzymes simultaneously in plant cells which have been transformed with them. Furthermore, the constructs can be introduced into plant mutants which are defective for one or more genes of starch biosynthesis (Shannon and Garwood, 1,984, in Whistler, BeMiller and Paschall, Starch: Chemistry and Technology, Academic Press, London, 2nd Edition: 25 -86). These defects can relate to the following proteins: starch-bound (GBSS I and II) and soluble starch synthases (SSS I and II), branching enzymes (BE I and II), "debranching" enzymes (R-enzymes), disproportionation enzymes and starch phosphorylases . This is only an example.

With the help of such a procedure it is also possible to inhibit the synthesis of several enzymes simultaneously in plant cells which have been transformed with them.

A large number of cloning vectors are available to prepare the introduction of foreign genes into higher plants, which contain a replication signal for E. coli and a marker gene for the selection of transformed bacterial cells. Examples of such vectors are pBR322, pUC series, M 1 3mp series, pACYC1 84 etc. The desired sequence can be introduced into the vector at a suitable restriction site. The plasmid obtained is used for the transformation of E. coli cells. Transformed E.coli cells are grown in a suitable medium, then harvested and lysed. The plasmid is recovered. Restriction analyzes, gel electrophoresis and other biochemical-molecular biological methods are generally used as the analysis method for characterizing the plasmid DNA obtained. After each manipulation, the plasmid DNA can be cleaved and DNA fragments obtained can be linked to other DNA sequences. Each plasmid DNA sequence can be cloned into the same or different plasmids.

A variety of techniques are available for introducing DNA into a plant host cell. These techniques include transformation plant cells with T-DNA using Agrobacterium tumefaciens or Agrobacterium rhizogenes as transformation agents, the fusion of protoplasts, the injection, the electroporation of DNA, the introduction of DNA using the biolistic method and other possibilities.

When injecting and electroporation of DNA into plant cells, there are no special requirements for the plasmids used. Simple plasmids such as e.g. pUC derivatives can be used. However, if whole plants are to be regenerated from such transformed cells, the presence of a selectable marker gene is generally necessary.

Depending on the method of introducing desired genes into the plant cell, additional DNA sequences may be required. E.g. If the Ti or Ri plasmid is used for the transformation of the plant cell, at least the right boundary, but frequently the right and left boundary of the Ti and Ri plasmid T-DNA as the flank region, must be linked to the genes to be introduced.

If agrobacteria are used for the transformation, the DNA to be introduced must be cloned into special plasmids, either in an intermediate vector or in a binary vector. The intermediate vectors can be integrated into the Ti or Ri plasmid of the agrobacteria on the basis of sequences which are homologous to sequences in the T-DNA by homologous recombination. This also contains the vir region necessary for the transfer of the T-DNA. Intermediate vectors cannot replicate in agrobacteria. Using a helper plasmid, the intermediate vector can be transferred to Agrobacterium tumefaciens (conjugation). Binary vectors can replicate in both E. coli and agrobacteria. They contain a selection marker gene and a linker or polylinker, which is from the right and left T-DNA border region are framed. They can be transformed directly into the agrobacteria (Holsters et al. Mol. Gen. Genet. 1 63 (1 978), 1 81 -1 87). The agrobacterium serving as the host cell is said to contain a plasmid which carries a vir region. The vir region is necessary for the transfer of the T-DNA into the plant cell. Additional T-DNA may be present. The agrobacterium transformed in this way can be used to transform plant cells.

The use of T-DNA for the transformation of plant cells has been intensively investigated and is sufficient in EP 1 20 51 6; Hoekema, In: The Binary Plant Vector System Offsetdrukkerij Kanters B.V., Alblasserdam (1 985), Chapter V; Fraley et al., Crit. Rev. Plant. Sci., 4, 1-46 and An et al. EMBO J. 4 (1 985), 277-287.

For the transfer of the DNA into the plant cell, plant explants can expediently be cultivated with Agrobacterium tumefaciens or Agrobacterium rhizogenes. The infected plant material (e.g. leaf pieces, stem segments, roots, but also protoplasts or suspension-cultivated plant cells) can then be removed in a suitable medium, which, among other things. certain sugars, amino acids, antibiotics or biocides for the selection of transformed cells can contain, whole plants can be regenerated again. The plants thus obtained can then be examined for the presence of the introduced DNA. Other possibilities of introducing foreign DNA using the biolistic method or by protoplast transformation are known (cf. for example Willmitzer, L., 1 993 Transgenic plants. In: Biotechnology, A Multi-Volume Comprehensive Treatise (HJ. Rehm, G. Reed, A Pühler, P. Stadler, eds.), Vol. 2, 627-659, VCH Weinheim-New York-Basel-Cambridge).

While the transformation of dicotyledonous plants via Ti plasmid vector systems with the help of Agrobacterium tumefaciens is well established, more recent ones Work on the fact that monocotyledonous plants can also be transformed using Agrobacterium-based vectors (Chan et al., Plant Mol. Biol. 22 (1 993), 491-506; Hiei et al., Plant J. 6 (1 994), 271-282).

Alternative methods for the transformation of monocotyledonous plants exist by means of the biolistic approach, the protoplast transformation or the physically or chemically induced DNA uptake in protoplasts, e.g. by electroporation of partially permeabilized cells, transfer of DNA using glass fibers, macro-injection of DNA into inflorescences, micro-injection of DNA into microspores or pro-embryos, DNA uptake by germinating pollen and DNA uptake in embryos by swelling (for an overview: Potrykus, Physiol. Plant (1 990), 269-273).

In the past, three of the above-mentioned transformation systems could be established for different cereals: the electroporation of tissue, the transformation of protoplasts and the DNA transfer by particle bombardment into regenerable tissue and cells (for an overview: Jahne et al., Euphytica 85 ( 1 995), 35-44).

The transformation of wheat is described variously in the literature (for overview: Maheshwari et al., Critical Reviews in Plant Science 1 4 (2) (1 995), 149 to 1 78): Hess et al. (Plant Sei. 72 (1 990), 233) used the macro-injection method to bring pollen and agrobacteria in close proximity. The mobilization of the plasmid, which contained the nptll gene as a selectable marker, was demonstrated by Southern blot analysis and NPTII test. The transformants showed a normal phenotype and were fertile. Kanamycin resistance has been demonstrated in two successive generations.

The first transgenic, fertile wheat plant, which after bombardment with microprojectile bound DNA could be regenerated by Vasil et al. (Bio / Technology 10 (1,992), 667-674). The target tissue for the bombardment was an embryogenic callus culture (type C callus). The bar gene which encodes a phosphinothricin acetyltransferase and thus imparts resistance to the herbicide phosphinothricin was used as the selection marker. Another system was developed by Weeks et al. (Plant Physiol. 102 (1,993), 1077-1084), and Becker et al. (Plant J. 5 (2) (1 994), 299-307). The target tissue for DNA transformation here is the scutellum of immature embryos, which was stimulated in an introductory in vitro phase to induce somatic embryos. The efficiency of the transformation lies with that of Becker et al. (loc cit.) developed system with 1 transgenic plant per 83 embryos of the "Florida" variety significantly higher than that of Weeks et al. established system with 1 to 2 transgenic plants per 1000 "Bohwhite" embryos.

The Becker et al. (loc. Cit) developed system forms the basis for the transformation experiments described in the examples.

Once the introduced DNA is integrated in the genome of the plant cell, it is generally stable there and is also retained in the progeny of the originally transformed cell. It normally contains one of the selection markers mentioned above, which e.g. Resistance to a biocide such as phosphinothricin or an antibiotic such as Kanamycin, G 41 8, bleomycin or hygromycin mediated or the selection of the presence or absence of certain sugars or amino acids allowed. The individually selected marker should therefore allow the selection of transformed cells over cells that lack the inserted DNA.

The transformed cells grow within the plant in the usual way (see also McCormick et al., Plant Cell Reports 5 (1 986), 81-84). The resulting plants can be grown normally and with plants that have the same transformed genetic makeup or other genetic makeup, are crossed. The resulting hybrid individuals have the corresponding phenotypic properties. Seeds can be obtained from the plant cells.

Two or more generations should be grown to ensure that the phenotypic trait is stably maintained and inherited. Seeds should also be harvested to ensure that the appropriate phenotype or other characteristics have been preserved.

The following examples are intended to illustrate the invention and do not represent any limitation.

1 . Cloning process

The vector pBluescript II SK (Stratagene) was used for cloning in E. coli.

2. Bacterial strains

The E. coli strain DH5α (Bethesda Research Laboratories, Gaithersburg, USA) was used for the Bluescript vector and for the antisense constructs. The E. coli strain XL1-Blue was used for the in vivo excision.

3. Transformation of immature wheat embryos

media

MS: 100 ml / l macro salt (D.Becker and H. Lörz, 1 ml / l micro salt Plant Tissue Culture

2 ml / l Fe / NaEDTA Manual (1 996), B 1 2: 1 -20) 30 g / l sucrose

# 30: MS + 2,4-D (2 mg / l)

# 31 MS + 2,4-D (2 mg / l) + phosphinothricin (PPT, active component of the herbicide BASTA (2 mg / l))

# 32: MS + 2,4-D (0.1 mg / l) + PPT (2 mg / l)

# 39: MS + 2,4-D (2 mg / ml) + 0.5 N mannitol / sorbitol each

The specified media were adjusted to pH 5.6 with KOH and solidified with 0.3% Gelrite.

The method for transforming immature embryos from wheat was developed and optimized by Becker and Lörz (D. Becker and H. Lörz, Plant Tissue Culture Manual (1 996), B1 2: 1 to 20).

In the experiments described below, the protocol developed by Becker and Lörz (loc. Cit) was followed.

For transformation, ears with caryopses of developmental level 1 are harvested 2 to 14 days after anthesis and surface sterilized. The isolated scutella are plated with the embryo axis facing the medium on induction medium # 30.

After 2 to 4 days of preculture (26 ° C, dark), the explants are placed on medium # 39 converted to the osmotic preculture (2 to 4 h, 26 ° C, dark).

Approximately 29 μg gold particles, onto which a few μg of the target DNA had previously been precipitated, are used for the biolistic transformation. Since the experiments carried out are co-transformants, the target DNA is added to the precipitation mixture in a ratio of 1: 1, consisting of the target gene and a resistance marker gene (bar gene).

4. DIG labeling of DNA fragments

The DNA fragments that were used as screening probes were labeled using a specific PCR with the incorporation of DIG-labeled dUTP (Boehringer Mannheim, Germany).

Media and solutions used in the examples:

20 x SSC 1 75.3 g NaCl

88.2 g sodium citrate ad 1000 ml with ddH ₂ O pH 7.0 with 10 N NaOH

The plasmid pTaSSI 8/1 was deposited at the DSMZ in Braunschweig, Federal Republic of Germany in accordance with the Budapest Treaty under number DSM 1 2794.

Example 1: Identification, isolation and characterization of a cDNA encoding a soluble starch synthase (SS I) from wheat (Triticum aestivum L., cv. Florida)

To identify the complete cDNA, which is an isoform of a soluble Starch synthase (SS I) encoded from wheat, the strategy of homologous screening was pursued. For this, a wheat cDNA library was screened with suitable oligonucleotides (screened). The SS I specific oligonucleotide used for screening was isolated using the 5'RACE method (Rapid Amplification of cDNA Ends) as described below.

The wheat cDNA bank was synthesized from poly (A) + RNA from approx. 20 day old caryopses (endosperm) in a Lambda Zap II vector analogous to the manufacturer's instructions (Lambda ZAP 11-cDNA Synthesis Kit, Stratagene GmbH, Heidelberg, Germany ). After determining the titer of the cDNA bank, a primary titer of 1.26 × 10 ⁶ pfu / ml could be determined.

Screening of the cDNA library was carried out with an SS I probe from wheat. A DNA fragment was isolated using 5'-RACE and the amplification of the 5'end was carried out using a 5'RACE kit (hereinafter "kit") from Boehringer (Mannheim, Germany). All steps were carried out in accordance with the manufacturer's instructions. Only reagents and enzymes from the kit were used, unless otherwise described.

First, poly (A) + RNA of approximately 20 days old caryopses was transcribed into single-stranded cDNA and used in a tailing reaction. The resulting cDNA provided in the 5 'region with the oligo (dA) anchor # 9 (kit) was amplified in a first reaction with the primers oligo (dT) # 8 (kit) and B2F5 according to a modified protocol as follows: 5 μl of thawed cDNA, 5 μl of 10 × reaction buffer (Life Technologies), 0.25 μM B2F5 primer, 0.75 μM oligo (dT) # 8, 0.2 mM dNTP's and 5U Taq polymerase (recombinant , Life Technologies). The PCR profile was: 94 ° C 3794 ° C 45 "/ 56 ° C 1 772 ° C 1 '30", 29 cycles / 72 ° C 5'. This was followed by a further PCR with the primers Oligo (dT) # 8 (kit),

B2F5 and the 5'-located primer B2F6. In a 50 μl mixture, 1 μl PCR product, 5 μl 10 × reaction buffer (Life Technologies), 0.25 μM

B2F5 primer, 0.25 µM B2F6 primer, 0.75 µM oligo (dT) # 8, 0.2mM dNTP's and

5U Taq polymerase (recombinant, Life Technologies) used. The PCR profile was:

94 ° C 3794 ° C 45 "/ 60 ° C 1 '/ 72 ° C 1 '30"; 29 cycles / 72 ° C 5 '

B2F5: 5'CCTCCCAATTCAAGGATTAGTG 3 '(Seq ID No. 3)

B2F6: 5'CCTCGCATGCAGCATAGCAA 3 '(Seq. ID No. 4)

The PCR products obtained by the above methods were separated in an agarose gel and the DNA fragments with a size greater than 800 bp were isolated. The PCR fragments were cloned using the pCR-Script SK (+) cloning kit from Stratagene (Heidelberg). Sequence analysis of the cloned subfragments identified approximately 1 50 bp previously unknown sequence of the SS I clone.

From the 5 'region of this new sequence, the oligonucleotides B2R00 and B2F6.2 were selected for the amplification of a DNA fragment (SS I probe), which was then labeled with digoxygenin-1 1 -UTP as described and as a probe for screening the wheat cDNA bank was used. The SS I probe was labeled by means of a PCR reaction with the primers B2R00 and B2F6.2 analogously to the information in "The DIG System Users Guide for Filter Hybridization" (Boehringer Mannheim).

B2R00: 5'TGTGGCTGCAAGTGAGGAGG 3 '(Seq. ID No.5)

B2F6.2 5'CCAGTCACAAACACGTAGCTACG 3 '(Seq. ID No.6) Approx. 700,000 phages were plated out to screen the wheat cDNA bank. The phages were plated out and the plates were stripped off according to standard protocols. The prehybridization and hybridization of the filters was carried out in 5X SSC, 3% blocking (Boehringer Mannheim), 0.2% Na dodecyl sulfate (SDS), 0.1% sodium lauryl sarcosine and 50 μg / ml herring sperm DNA at 65 ° C. 1.3 ng / ml of the DIG-labeled SS I probe was added to the hybridization solution and the hybridization was incubated overnight. The filters were washed according to the protocol as described in "The DIG System User's Guide for Filter Hybridization" (Boehringer Mannheim) at 65 ° C. Positive clones were isolated by two more rounds of screening. Individual clones were obtained as in vivo excision as pBluescript SK phagemids (carried out analogously to the manufacturer's instructions; Stratagene, Heidelberg).

After analysis of the clones via mini-preparation and restriction of the plasmid DNA, the clone TaSSI 8/1 was further analyzed.

Example 2: Sequence analysis of the cDNA inserts of the plasmid pTaSSI 8/1

The plasmid DNA was isolated from the clone TaSSI 8/1 and the sequence of the cDNA insertions was determined using the dideoxynucleotide method (Sanger et al., Proc. Natl. Acad. Sci. USA 74 (1 977), 5463-5467). The insertion of the clone TaSSI 8/1 is 2805 bp long and represents a complete cDNA. The nucleotide sequence is shown under Seq ID No. 1 specified. The corresponding amino acid sequence can be found under Seq ID No. 2 specified. A comparison with previously published sequences showed that the under Seq ID No. 1 sequence is new and includes a complete coding region.

Example 3: Preparation of the plant transformation vector pTa-gamma-SSI-8/1

The expression of the cDNA isolated under Example 1 was based on constructed from pUC1 9 as the base plasmid the plant transformation vector pTa-gamma-SSI-8/1. To construct the vector, the cDNA insertion of the plasmid TaSSI 8/1 is connected completely in sense orientation to the 3 'end of the ubiquitin promoter. This promoter consists of the first untranslated exon and the first intron of the ubiquitinl gene from maize (Christensen AH et al., Plant Molecular Biology 1 8 (1 992), 675-689). Parts of the polylinker and the NOS terminator originate from the plasmid pACT1 .cas (CAMBIA, TG 0063; Cambia, GPO Box 3200, Canberra ACT 2601, Australia). Vector constructs with this terminator and constructions based on pActl .cas are described in MCElroy et al. (Molecular Breeding 1 (1 995), 27-37). The resulting vector was called pUbi.cas.

The expression vector was cloned by restricting a fragment from the clone TaSSI 8/1 with the restriction enzymes Xba I and Ssp. I. The fragment was filled in at the ends using a Klenow reaction and then ligated into the Sma I cloning site of the expression vector pUbi.cas. The resulting expression vector was called pTA-gamma-SSI 8/1. In a second construct, the 5'-untranslated leader of the clone TaSSI-8/1 was first removed by treatment with exonnuclease. The cloning into the expression vector pUbi.cas was then carried out. This construct was called Ta-gamma-SSI-8/1 -2.

The vectors pTa-gamma-SSI-8/1 and pTa-gamma-SSI-8/1 -2 are then used to transform wheat. INTERNATIONAL FORM

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Claims

Claims:

1 . Nucleic acid molecule encoding a protein having the function of a wheat starch synthase selected from the group consisting of

(a) a nucleic acid molecule which encodes a protein which has the sequence shown in Seq ID NO. 2 includes the given amino acid sequence,

(b) a nucleic acid molecule which has the properties listed under Seq ID No. 1 comprises a nucleotide sequence shown or a part thereof or a corresponding ribonucleotide sequence;

(c) a nucleic acid molecule which hybridizes with or is complementary to one of the nucleic acid molecules mentioned under (a) or (b), and

(d) a nucleic acid molecule whose nucleotide sequence deviates from the sequence of a nucleic acid molecule mentioned under (a), (b) or (c) due to the degeneration of the genetic code.

2. Nucleic acid molecule according to claim 1, characterized in that it is a DNA molecule.

3. DNA molecule according to claim 2, characterized in that it is a cDNA molecule.

A nucleic acid molecule according to one or more of claims 1 to 3, which contains regulatory elements.

5. Nucleic acid molecule according to claim 1, characterized in that it is an RNA molecule.

6. A nucleic acid molecule that hybridizes specifically with a nucleic acid molecule according to any one of claims 1 to 5.

7. The nucleic acid molecule of claim 6, which is an oligonucleotide at least 15 nucleotides in length.

8. vector containing a DNA molecule according to any one of claims 1 to 5.

9. Vector according to claim 8, wherein said nucleic acid molecule is linked in sense orientation to regulatory elements which ensure the transcription and synthesis of a translatable RNA in pro- or eukaryotic cells.

10. The vector of claim 8, wherein said nucleic acid molecule is linked in sense orientation to regulatory elements which ensure the synthesis of a non-translatable RNA in pro- or eukaryotic cells.

1 1. A vector according to claim 8, wherein said nucleic acid molecule is linked in antisense orientation to regulatory elements which ensure the synthesis of a non-translatable RNA in pro- or eukaryotic cells.

A host cell transformed with a nucleic acid molecule according to one or more of claims 1 to 5 or a vector according to one or more of claims 8 to 1 1 or which is derived from such a cell.

3. Protein encoded by a nucleic acid molecule according to one or more of claims 1 to 4.

14. A method for producing a protein according to claim 1 3, wherein a host cell according to claim 1 2 is cultivated under conditions which the Allow synthesis of said protein and said protein is isolated from the cultured cells and / or the culture medium.

1 5. A method for producing a transgenic plant cell, wherein a) a nucleic acid molecule according to one or more of claims 1 to 5 or b) a vector according to one or more of claims 8 to 1 1 is integrated into the genome of a plant cell.

1 6. Transgenic plant cell which has been transformed with a nucleic acid molecule according to one or more of claims 1 to 5 or a vector according to one or more of claims 8 to 1 1 or which is derived from such a cell.

1 7. A method for producing a transgenic plant cell, wherein a1) a nucleic acid molecule according to one or more of claims 1 to 5 or a2) a vector according to one or more of claims 8 to 1 1 is integrated into the genome of a plant cell and b) a whole plant is regenerated from said plant cell.

18. Plant containing a plant cell according to claim 1 6.

1 9. Plant according to claim 1 9, which is a monocot or dicot plant.

20. Plant according to claim 1 9, which is a useful plant.

21. A plant according to claim 20 which is a starch storing plant.

22. The plant of claim 21 which is a corn, rice, potato or wheat plant.

23. Plant propagation material according to one or more of claims 1 8 to 22.

24. Starch, obtainable from a plant cell according to claim 1 6, a plant according to one or more of claims 1 8 to 22 or from propagation material according to claim 23.

25. Use of the starch according to claim 24 for the production of foods or food precursors, preferably baked or pasta.

26. Use of the starch according to claim 24 for the production of packaging materials or disposable items.