Regulation of starch synthesis in higher plants

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Starch is the primary source of calorific intake for mankind. As a commodity, it has wide application in the food and non-food sectors. As a food-stuff, particular types of starch known as resistant starch (RS) provide additional health benefits because of their effects on the rate of glucose absorption into the blood stream and through a pre-biotic function in the large colon where RS contributes to dietary fibre with positive benefits for colorectal health. Within the non-food sector it has many applications, including areas as diverse as the paper and board industry, biodegradable plastics, drug delivery, dry-wall manufacture, and as a replacement for hydrocarbon ingredients in paint. Increasingly it is being used as a feedstock in the energy industry for the production of bio-ethanol as an alternative to fossil fuels. Starch is a polymer made of glucose units joined together in linear chains with periodic branching giving rise to a highly organized, semi-crystalline, insoluble structure. It is biological variation in the fine-structure of starch which gives rise to its diversity of application and functionality. Despite its enormous significance for mankind, our fundamental knowledge of how it is made is still lacking to the point where we are not in a position to produce tailor-made starches for particular end-uses, other than through the use of significant chemical modification which often has deleterious environmental impact as a result of effluent by-products. Starch synthesis is dependent upon the cooperative activities of a large number of enzymes. The work described in this program of research will address basic questions about biochemical mechanisms which give rise to the coordinated interaction of the enzymes involved. In particular, the higher order mechanisms which facilitate biosynthesis of the starch granule will be investigated, including the formation of large multi-enzyme complexes in vivo. Understanding these mechanisms will provide increased opportunity for future biotechnological application.