Physiological Function of Rice Sucrose Synthase Controlled by Phosphorylation Involved in Sucrose Metabolism

Abstract

Sucrose synthase catalyzes a first step for sucrose metabolism at sink organs. The sucrose catabolites are utilized for cellulose and starch synthesis, therefore sucrose synthase is one of the key enzyme for storage material synthesis in sink organs. In rice, three isozymes of sucrose synthase have been identified (Susy1, Susy2 and Susy3). We have found the involvement of SPK (Seed-development specific Protein Kinase) for the phosphorylation of Susy in rice pre-mature seeds. Thus we investigated the effect for phosphorylation of Susy by SPK, and we obtained data where it was indicated that the rice sucrose synthase were regulated by phosphorylation in vitro. Further more, we revealed that rice Susys could utilize ADP as well as UTP, in both reactions, sucrose degradation and sucrose synthesis, respectively.