Isolation and analysis of function of starch synthase IIIa using transposon tagging in rice.

Abstract

There are 10 starch synthase (SS) isozymes in rice. With the exceptions of GBSSI, SSI and SSIIa, their functions in starch biosynthesis are poorly understood. SSI and SSIII account for the major SS activity in developing maize endosperm. The SSIII-deficient mutant dull-1 in maize is well known, but no SSIII mutants in rice have been identified so far. In this study, we isolated an SSIIIa mutant from about 40,000 knockout rice population. In the mutant, Tos17 was inserted in exon 1 of the SSIIIa gene and the SSIIIa band on Native-PAGE/SS activity staining gel was completely absent. The proportion of α-polyglucan chain with DP of DP6-8, 17-18, 31-70 in amylopectin of endosperm starch was reduced and DP10-15, 20-29 was increased compared to wild type ones. The functions of SSIIIa of starch biosynthesis in rice endosperm are discussed.