Modifying Starch Biosynthesis with Transgenes in Potatoes

A large amount of the CO2 fixed by green plants is stored as reserve starch in plant tissues such as seeds, tubers, and roots. At present, this starch is used either directly for food or processed to yield starches with food and industrial uses. Worldwide, approximately 3 to 5% of the starch crop produced is used for the production of starch. The majority of this is processed into high fructose syrup or dextrose. Approximately one-third is used for nonfood purposes, such as in the paper, packaging, and textile industries. Various regional and varietal differences in the utilization of starch crops exist. For example, one-quarter of the world's potato starch is produced in The Netherlands. Genetic engineering of plants in conjunction with molecular biology and a knowledge of starch biosynthesis offers the promise of being able to use this vast plant resource to produce new or altered carbohydrates. These carbohydrates could have increased or unique value for food or industrial purposes. In this review, we discuss early progress that has been made in this area by engineering transgenic potatoes (Solanum tuberosuni). This technology should be applicable to other starch crops, including corn and rice. In starch-storing organs such as the potato tuber, starch is stored in plastids called amyloplasts. The exact pathway for starch conversion is still open to debate but a general pathway can be outlined (see refs. 16 and 17 for comprehensive