There is a great consideration on rice eating quality aside from improving its tolerance to various stresses. High yielding and pest and disease tolerant rice is highly desirable but it is more commercially important if it also has a high eating quality. There are various factors contributing to the good eating quality of rice. This study focuses on modifying the expression of GBSS1 genes which are responsible for amylopectin and amylose synthesis in rice by using RNAi and antisense techniques. We have developed 40 transgenic plants with RNAi-GBSS1 gene and 60 transgenic lines with antisense-GBSS1 gene. The transgenic plants show diverse amylose contents in rice seed. We selected candidate lines according to PCR, RNA expression and amylose contents. A semi-quantitative RT-PCR was carried out to measure the expression level of GBSS1 gene at several time points after the flowering of transgenic plants. The expression level of GBSS1 gene in rice grains decreases over time and the mRNA expression among the transgenic plants were lower compare to its wild type. In the SEM analysis, the starch granule of wild type Gopumbyeo has very large structures accompanied with small ones around the area. However, the starch structures in transgenic plants were smaller and more uniform in size and shape throughout the viewing area

An increasing preference for good eating quality of rice among consumers has become one of the important considerations in rice breeding. Amylose content of starch is one of the important factors of rice eating quality. Amylose composition is determined by the relative activity of soluble starch synthase (SSS) and granule-bound starch synthase (GBSS). This study focuses on modifying the expression of SSS1 gene which is responsible for amylopectin and amylose synthesis in rice by using RNA interference (RNAi) and antisense technology. The transgenic rice plants showed various amylose content (9-17%) in rice seed. Candidate rice lines were selected according to PCR, RNA expression and amylose contents analyses. A semi-quantitative RT-PCR was carried out to determine the expression level of SSS1 gene at several time points after the flowering of transgenic plants. Downregulation of SSS1 gene in transgenic rices was evident in the decreasing expression in rice grains over time. Accordingly, SEM micrographs analysis revealed uniform size with smooth curves starch granules in downregulation rice lines, in contrast with the non-uniform granules in wild type.

Amylopectin composition is determined by the relative activity of soluble starch synthase (SSS) and granule-bound starch synthase (GBSS). Soluble starch synthase and starch branching enzymes are major determinants for the synthesis of amylopectin while GBSS1 is responsible for amylose synthesis in vivo. The formers are made of linear and branched molecules and the latter is composed of highly branched molecules. To increase the palatability of rice, down-regulation of amylose synthesis by antisense and RNA interference (RNAi) could be excellent and powerful tools for controlling the starch composition which is responsible for grain eating quality. The goal of this study is to generate breeding lines with lower amylose content relative to its wild type. This study also reports the results of the two down-regulating technology in lowering the amylose content of rice grain. Furthermore, this study elucidates the effect of using antisense and RNAi for SSS1 and GBSS1.