DNA molecules that code for enzymes involved in starch synthesis

Details DNA molecules that code for enzymes involved in starch synthesis DNA molecules that code for enzymes involved in starch synthesis

1997-07-24

2000-10-10

Fox, David T.

Multicellular living organisms and unmodified parts thereof and

Method of introducing a polynucleotide molecule into or...

The polynucleotide alters carbohydrate production in the plant

800298, 8003172, 435 691, 435101, 4353201, 435419, 435468, 536 236, C12N 1529, C12N 1582, C12P 1904, A01H 500

Patent

active

061303674

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to DNA molecules encoding enzymes which are involved in the starch synthesis of plants. These enzymes represent two different isotypes of the soluble starch synthase as well as a starch granule-bound starch synthase.
This invention furthermore relates to vectors, bacteria, as well as to plant cells transformed with the DNA molecules described and to plants regenerated from them.
Also, processes for the production of transgenic plants are described which, due to the introduction of DNA molecules encoding soluble or starch granule-bound starch synthases, synthesize a starch which is modified as regards its properties.


BACKGROUND OF THE INVENTION

With respect to its increasing significance which has recently been ascribed to vegetal substances as regenerative sources of raw materials, one of the objects of biotechnological research is to try to adapt vegetal raw materials to the demands of the processing industry. In order to enable the use of modified regenerative raw materials in as many areas as possible, it is furthermore important to obtain a large variety of substances.
Apart from oils, fats and proteins, polysaccharides constitute the essential regenerative raw materials derived from plants. Apart from cellulose, starch maintains an important position among the polysaccharides, being one of the most significant storage substances in higher plants. Besides maize, rice and wheat, potato plays an important role as starch producer.
The polysaccharide starch is a polymer made up of chemically homogeneous basic components, namely the glucose molecules. However, it constitutes a highly complex mixture from various types of molecules which differ from each other in their degree of polymerization and in the degree of branching of the glucose chains. Therefore, starch is not a homogeneous raw material. One differentiates particularly between amylose-starch, a basically non-branched polymer made up of .alpha.-1,4-glycosidically branched glucose molecules, and amylopectin-starch which in turn is a complex mixture of various branched glucose chains. The branching results from additional .alpha.-1,6-glycosidic interlinkings. In plants which are typically used for starch production, such as, e.g., maize or potato, the synthesized starch consists of about 25% of amylose starch and of about 75% of amylopectin starch.
In order to enable as wide a use of starch as possible, it seems to be desirable that plants be provided which are capable of synthesizing modified starch which is particularly suitable for various uses. A possibility of providing such plants is--apart from breeding--in the specific genetic modification of the starch metabolism of starch-producing plants by means of recombinant DNA techniques. However, a prerequisite therefor is to identify and to characterize the enzymes involved in the starch synthesis and/or the starch modification as well as to isolate the respective DNA molecules encoding these enzymes.
The biochemical pathways which lead to the production of starch are basically 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.
The most important enzymes involved in starch synthesis are starch synthases as well as branching enzymes. In the case of starch synthases various isotypes are described which all catalyze a polymerization reaction by transferring a glucosyl residue of ADP-glucose to .alpha.-1,4-glucans. Branching enzymes catalyze the introduction of .alpha.-1,6 branchings into linear .alpha.-1,4-glucans.
Furthermore, it is discussed that other enzyme activities, such as hydrolytic or phosphorolytic activities, are involved in the synthesis of starch (Preiss in Oxford Survey of Plant Molecular and Cell Biology, Oxford University Press, Vol. 7 (1991), 59-114). It can furthermore not be precluded that the "R enzyme", or the so-called disproportionizing enzyme, and the starch phosphor

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Nakatani et al. Jpn. J. Crop Sci. 61(3): 463-468, 1992.
Edwards et al. Plant J. 8(2): 283-294, 1995.
T. Baba et al., "Identification, cDNA Cloning, and Gene Expression of Soluble Starch Synthesis in Rick (Oryza sativa L.) Immature Seeds", Plant Physiol, 103, pp. 565-573 (1993).
I. Dry et al., "Characterization of cDNAs Encoding Two Isoforms of Granule-Bound Starch Synthase Which Show Differential Expression in Developing Storage Organs of Pea and Potato", The Plant Journal, 2(2), pp. 193-202 (1992).
S.N.I.M. Salehuzzaman, et al., "Isolation and Characterization of a cDNA Encoding Granule-Bound Starch Synthase in Cassava (Manihot Esculenya Crantz) and its Antisense Expression in Potato", Plant Molecular Biology, 23, pp. 947-962 (1993).

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