Transgenic Plants Production of Starch, Cereals, Legumes, Tubers, Roots, Potato, Yam, Cassava, Amylose, Glucan Polymer

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Home >> Plant Biotechnology and Genomics >>Molecular Farming Pharming >>Transgenic Plants Production of Starch

	Production of starch Several species of higher plants are used for their stored starch. These include (i) seeds of cereals and legumes and (ii) tubers/roots of potato, yam and cassava. In potato, 75% of dry weight is starch, making it a model system for improvement in starch quantity and quality. However, corn produces 17 million tons of starch as against potato producing 2 million tons per year; but transgenics in com are more difficult to produce and potato starch is certainly better. There are two major components of starch, first, amylose (mol. wt. 104 to 106), which is a linear a(1-4) D-glucan polymer and second, amylopectin (mol. wt. 104), which is a branched a (1-4 and 1-6) D- glucan polymer.
Besides these two components, starch also contains small amounts of lipids, proteins and phosphorus, which determine the starch quality. In higher plants, starch is found in two types of plastids, chloroplasts accumulating transitory starch (larger granules) and amyloplasts containing amylose. Amylose makes up to 11-37% of total reserve starch, but mutants with low and high amylose contents are known. The most important are the amylose free (waxy) mutants, which can be identified by staining with iodine (reddish brown colour in amylose free starch).
Starch is mainly used as a thickener in the food (e.g. sauce) and as sweetener in beverage industries (drinks, confectionery); about one third is also used either in paper, packaging and textile industry or as a raw material in chemical industry (production of ethanol, fructose and gluconate). For its industrial use, starch has to compete with cellulose or crude oil. It also needs to be modified according to need. For instance, starch from waxy maize resembles that from tapioca and has been used as its substitute, when tapioca was not available (Second World War).
The demand for amylose free starch may increase, since it is easily digestible and can make clear pastes, that do not, retrograde (retrogradation means precipitation of amylose in aqueous solution of starch), when cooked as microwave-ready food. There is also a demand for high amylose crop plants for other purposes. Starch is variously modified after isolation, 80% of potato starch being used only in a modified form (e.g. derivatized or gelatinized starches). Derivatized starch is used to improve paper strength and gelatinized starch is used to modify food texture. Thus starch production in crop plants needs to be modified for its variety of uses. Transgenic approaches may help in this direction.
	Most of the starch in higher plants is synthesized from sucrose involving at least 13 enzymes, of which only the following three are considered as the key enzymes: (i) ADP-glucose pyrophosphorylase (AGPase), (ii) soluble starch synthase (SSS) and (iii) branching enzyme (BE). A number of these genes in starch biosynthesis have been isolated and are available for use in the production of transgenic plants. Following results using techniques of genetic engineering have been obtained in potato. (i) Antisense approach was successfully persued for inhibiting the action of granule-bound starch synthase (GBSS) enzyme.

This led to 70%-100% inhibition of the activity of this enzyme resulting in decrease or complete absence of amylose content, thus giving amylose free starch. (ii) Starch content could be increased by introducing a bacterial gene encoding AGPase (glgC) into potato, coupled with strong promoter belonging to patatin gene. This promoter induces high expression in tuber. DNA sequence for a transit peptide was also attached directing the starch to chloroplasts. Starch content was increased by at least 50%

Production of mannitol
Transfer of a gene for mannitol dehydrogenase from E. coli to tobacco was achieved, which led to increase in the level of mannitol in transgenic tobacco plants.

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Factors Affecting Choice of Transgenic Plants for Vaccines Transgenic Tobacco, Potato and Banana as Edible Vaccines Transgenics as Edible Vaccines for Hepatitis B The Production of Vaccines in Transgenic Plants Alternative to Transgenic Plant for Vaccine Production Transgenic Plants for Antibodies Production of Antibodies in Transgenic Plants Transgenic Plants as Factories for Biopharmaceuticals Production of Biopharmaceuticals in Transgenic Plants Production of Glucocerebrosidase for 'Gaucher's Disease' Production of Hirudin (an Anticoagulant) for 'Thrombosis'