Chalk5调控水稻垩白形成的生理、细胞与分子机理

Grain chalkiness in rice negatively affects appearance quality, cooking and eating quality, head yield and market values, and so it is one of the most important quality traits in rice. In the previous study, we cloned the first major QTL gene, Chalk5, controlling grain chalkiness rate in rice, however its regulating mechanisms are unknown. In this project based on the previous works, we plan to investigate the physiological factors of pH values, temperature and the rate and directions of water loss in chalky endosperms that lead to the formation of grain chalkiness, and to discover the cellular causes that these factors result in. Moreover, in order to uncover the molecular network of Chalk5 that regulating the formation of rice grain chalkiness, the putative up-stream regulating proteins and interacting proteins of Chalk5 will be identified using the analyses of Y1H, trans-factors, Y2H, IP-MS and screening of suppressors, and confirmed using both biochemical and genetic evidences, including EMSA, Co-IP, BiFC, and genetic transformation or mutant analyses, respectively. The findings in this project will not only make great contributions to our understanding in regulating mechanisms of grain chalkiness and endosperm development, but also provide theories and tools for molecular breeding of high-quality rice, making good sense in both theory and practice.

垩白直接影响稻米的外观品质、蒸煮食味品质、精米产量和市场价值，是水稻最重要的品质性状之一。在前期研究工作中，申请人克隆了控制水稻垩白的第一个主效QTL基因Chalk5，但其调控机理不清楚。本项目在其工作基础上，通过研究胚乳pH值、温度、失水的速率和方向性等因素对垩白形成的影响，来确定Chalk5调控垩白形成的生理学原因以及它们所导致的细胞原因；通过酵母单杂交、启动子反式作用因子、酵母双杂交、免疫沉淀-质谱联用、垩白抑制子筛选等分析鉴定Chalk5上游调控蛋白和互作蛋白，再用凝胶阻滞、免疫共沉淀、双分子荧光互补、突变体或转基因等技术对调控蛋白和互作蛋白进行生化与遗传上的双重验证，来剖析Chalk5等位基因在胚乳特异表达与差异表达的分子原因及其调控垩白形成的分子网络。本研究的完成，不仅将增进对稻米垩白调控机制的认识，还将为水稻优质稻分子育种提供理论基础与技术保障，在理论和实践上具重要意义。

垩白直接影响稻米的外观品质、蒸煮食味品质、精米产量和市场价值，是水稻最重要的品质性状之一。前期研究工作中，实验室成功分离克隆了控制水稻垩白的第一个主效QTL基因Chalk5，但其调控机理不清楚。本项目在其研究基础上，围绕Chalk5胚乳特异与差异表达的原因、引起腹白极性产生的原因以及调控垩白形成的分子机理3个方面开展研究。主要研究结果如下：(1) Chalk5在胚乳的特异表达受组蛋白甲基转移酶FIE1和组蛋白去甲基化酶JMJ705介导的H3K27me3修饰调控；(2) Chalk5胚乳差异表达受上游调控蛋白复合体（主要有bZIP58、ABI3、B3类转录因子、组蛋白取甲基化酶JMJ705等）对变异序列的差异调控；(3) 稻米腹白极性的产生与Chalk5及其上游调控蛋白基因bZIP58、淀粉水解酶基因以及种子贮藏物质合成基因的背腹极性表达密切相关，且发育后期腹部较高含水量也是引起腹白极性形成的重要原因；(4) Chalk5及其关键调控因子bZIP58基因均受高温诱导表达，且高温下种子的垩白度会加强。本研究的完成，不仅将增进对稻米垩白调控机制和胚乳发育的认识，还将为水稻优质稻分子育种提供理论基础与技术保障，在理论和实践上具有重要意义。