Naturally Occurring Variations in Starch Synthase Isoforms in Rice Endosperm

Abstract

We genetically analyzed cooked rice quality differences between japonica and indica rice varieties . By using backcross inbred lines, substitution, and near isogenic lines, we confirmed that at least 3 chromosomal regions affect cooked rice quality as measured by a Mido Meter. Each of these regions contains a locus for the starch synthase isoform, granule-bound starch synthase I (GBSSI), starch synthase I, and starch synthase ha (SSIIa). We found naturally occurring variations in GBSSI (Wx protein) amount and SSIIa activity that greatly affect cooked rice quality by altering amylose content for GBSSI or amylopectin structure for SSIIa. In sensory tests, effects of GBSSI variation were clear even just after cooking, but those of SSIIa became clear only after cooling.