Functional alteration and gene expression of enzymes for plant starch biosynthesis

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ADP-Glucose is a sole glucose donor for plant starch biosynthesis and is synthesized from glucose1-phosphate and ATP by ADPglucose pyrophsophorylase (AGPase ; EC 2.7.7.27). Plant AGPases are allosterically regulated by 3-phosphoglycerate and Pi. In plant leaves, the allosteric regulation of AGPases controls the rate of tansitory starch synthesis. The aim in this study was to extensively analyze the effect of allosteric properties on starch content in leaves and to enhance tha productivity by expression of allosterically mutated AGPase in plants.1) The gene for mutated AGPase whose allosteric sensitivities are decreased was introduced Arabidopsis mutant plant (TL46) decreasing AGPase activity in leaves.2) The AGPase activity in leaves of transgenic plants increased more than 10-and 1.5-fold of those of TL46 and wild-type plants, respectively.3) The maximum starch level and turnover of starch in leaves of transgenic plants was about 1.3 and 1.8 times higher, respectively, than those in wild-type plants. Additionally, in transgenic plants the dry weight of leaves and leaf area were increased 1.8-fold of those in wild-type plants.4) The total seed number of transgenic plants was about 1.3 times higher than that of wild-type plants.These results show that the decreased sensitivity of AGPase for allosteric effectors generate the increase of starch levels, plant growth and yield, suggesting that the allosteric properties of AGPase not only regulate the rate of starch biosynthesis but influence plant growth and biomass.