ARS | Publication request: Potential Targets for Seed Improvement through Bioengineering Starch Synthesis Pathways

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 18, 2009
Publication Date: July 22, 2009
Citation: Cao, F., Cao, H. 2009. Potential targets for seed improvement through bioengineering starch synthesis pathways (abstract). Plant Biology 2009, July 18-22, Honolulu, Hawaii.

Technical Abstract: Starch is the principle carbohydrate in the food chain and is a renewable and biodegradable polymer widely used in the food, beverage, paper, textile, and livestock feed industries. It is the major component of the harvestable organs in many agronomic plants. The quantity and quality of starch thus affects crop yield and industrial uses. This has generated great interest in understanding starch biosynthesis pathway. According to the current model, the substrate ADP-glucose is mainly produced in the cytosol by ADP-glucose pyrophosphorylase (AGPase, transferred into amyloplast by adenylate translocator (ANT), and utilized in the synthesis of linear chains by starch synthase (SS). Starch structure is further determined by the activities and specificities of branching enzyme (BE) and debranching enzyme (DBE), and by their interactions with SS and other proteins. Each biochemical step is catalyzed by several isoforms. For example, maize seed has at least two forms of AGPase, ANT, and DBE, 3 forms of BE, and five forms of SS. Starch amount is dramatically reduced by down-regulation of AGPase and ANT, as evidenced from the mutations at the bt1, bt2, and sh2 loci. Starch structure is significantly altered by down-regulation of SS, BE, and DBE, as evidenced from the mutations at the du1, wx1, ae1, and su1 loci. Alteration of starch quantity and quality is also observed in transgenic plants with up- or down-regulation of key enzyme activities in the starch synthesis pathway. Since starch constitutes more than 70% of the dry weight in those seeds and starch synthesis is the predominant biochemical event in seed development, the quantity and quality of nutritionally important protein and oil could be improved by directing certain portion of carbons from starch synthesis.