Amyloplast Membrane Protein SUBSTANDARD STARCH GRAIN6 Controls Starch Grain Size in Rice Endosperm

摘要

Starch is a biologically and commercially important polymer of glucose. Starch is organized into starch grains (s) inside amyloplasts. The size differs depending on the plant species and is one of the most important factors for industrial applications of starch. There is limited information on genetic factors regulating sizes. In this study, we report the rice (Oryza sativa) mutant substandard starch grain6 (ssg6), which develops enlarged s in endosperm. Enlarged s are observed starting at 3 d after flowering. During endosperm development, a number of smaller s appear and coexist with enlarged s in the same cells. The ssg6 mutation also affects morphologies in pollen. The SSG6 gene was identified by map-based cloning and microarray analysis. SSG6 encodes a protein homologous to aminotransferase. SSG6 differs from other rice homologs in that it has a transmembrane domain. SSG6-green fluorescent protein is localized in the amyloplast membrane surrounding s in rice endosperm, pollen, and pericarp. The results of this study suggest that SSG6 is a novel protein that controls size. SSG6 will be a useful molecular tool for future starch breeding and applications.