Modification of Starch Composition Using RNAi Targeting Soluble Starch Synthase I in Japonica Rice

An increasing preference for good eating quality of rice among consumers has become one of the important considerations in rice breeding. Amylose content is a leading factor affecting eating quality of rice. Amylose composition is determined by the relative activity of soluble starch synthase (SSS) and granule-bound starch synthase (GBSS). This study focused on modifying the expression of SSSI gene which is responsible for amylopectin and amylose synthesis in rice by using RNA interference (RNAi) technology. The transgenic rice plants showed various amylose contents (11-17%) in rice grains. Favorable rice lines were selected according to genomic PCR, transgene expression and amylose contents analysis. A semi-quantitative RT-PCR was carried out to determine the expression level of SSSI gene after flowering of transgenic rice and wild type. Down-regulation of SSSI gene in transgenic plants was evident in the decreasing expression in rice grains. Accordingly, scanning electron microscopy (SEM) analysis revealed uniform size with smooth curves starch granules in down-regulation rice lines, in contrast with the non-uniform granules in wild type. Results indicated that RNAi-SSSI transgenic lines produced low amylose contents that fell between glutinous and non-glutinous rice. This study showed that down-regulation of endogenous SSSI may improve the eating quality in rice.