粮食高产、优质是作物基础科学和应用科学研究的重要目标之一。对于水稻等很多禾本科作物而言，种子大小是一个重要的产量性状、外观品质性状和人工驯化的靶性状，但人们对作物种子大小调控的分子机理认识有限。GS5是在我国水稻生产中发挥重要作用的、正调控水稻种子大小和千粒重的功能基因。本项目是申请人及其所在课题组最近分离克隆的该功能基因工作的一个延续。初步的研究结果表明，GS5的功能性遗传变异集中在其启动子上的18处变异中，但尚不清楚究竟是哪个或者哪些自然变异是其功能性变异。本项目拟以GS5启动子的系列缺失片段和定点诱变片段的遗传转化为技术手段、以其报告基因酶活检测和种子大小表型分析为研究内容，鉴定并验证GS5基因调控种子大小的功能性自然变异位点，揭示其自然变异的分子调控机理。本研究结果，不仅对阐明种子大小自然变异和人工驯化的分子机制有重要科学意义，而且还将为稻米粒形和千粒重的分子育种提供理论依据。

Increasing grain yield and improving grain quality of food crops are among the most important goals of crop basic and applied science research. In rice and many other cereals, grain size is an important yield trait, appearance quality trait and a target trait of both domestication and artificial breeding. However, little is known on the molecular mechanism of grain size regulation in crops. GS5, playing an improtant role in rice production of China, is a functional gene positively controlling rice grain size and 1000-grain weight, which is recently isolated by our group. In our previous study, it is found that the functional variations of GS5 are among the 18 variations in the promoter region, however, we do not know which variation is the functional variation of grain size. In this project, we focus on identifying the functional variations of GS5 that control grain size variation in rice by the genetic transformation analysis with promoter fragments obtained by serial deletions and site-directed mutations, to uncover the molecular mechanism of the natural variation. The results of the study will not only contribute to exploring the molecular mechanism of natural variation and domestication of grain size, but also provide the important information for molecular breeding of rice grain size and 1000-grain weight.