A Novel Mutation of , Encoding Pyruvate Orthophosphate Dikinase, Affects Metabolism and Structure of Starch in the Rice Endosperm.

Starch, as a main energy storage substance, plays an important role in plant growth and human life. Despite the fact that several enzymes and regulators involved in starch biosynthesis have been identified, the regulating mechanism of starch synthesis is still unclear. In this study, we isolated a rice floury endosperm mutant from a mutant pool induced by Co. Both total starch content and amylose content in seeds significantly decreased, and starch thermal and pasting properties changed. Compound starch granules were defected in the floury endosperm of seeds. Map-based cloning and a complementation test showed that the floury endosperm phenotype was determined by a gene of , which encodes pyruvate orthophosphate dikinase (PPDK, EC 2.7.9.1). Subcellular localization analysis demonstrated that PPDK was localized in chloroplast and cytoplasm, the highly expressed in leaf and leaf sheath, and the constitutively expressed with a high expression in developing endosperm. Moreover, the expression of starch synthesis-related genes was also obviously altered in developing endosperm. The above results indicated that PPDK played an important role in starch metabolism and structure in rice endosperm.