一个水稻显性抗白叶枯病突变基因的克隆与功能分析

Bacterial blight is one of the most serious diseases causing rice yield loss, so mining and utilizing new disease resistance genes is of great significance to breeding new rice varieties resistant to diseases. In this study, the highly susceptible restorer line 3550(R3550) was used for mutation with EMS, then we found a gain-of-function mutant resistant to blight bacteria, T1247. Lesion length on leaves of T1247 and R3550 showed obvious difference after inoculated with Xoo. Genetic analysis showed that the resistant trait of T1247 was controlled by a single dominant nuclear gene. The candidate gene was mapped on the long arm of chromosome 11 through BSA-Seq, which was a new gene and was named Xa45 tentatively. Different from those typical resistance genes, Xa45 has no LRRs region and is an atypical resistance gene. At the same time, the T1247 mutant showed no significant difference in agronomic characters to the high yield restorer line R3550 which is already spread and applied in large area, thus the T1247 mutant and its dominant mutant gene have potential application in resistance varieties breeding. Based on previous work of this study, function of Xa45 will be identified using transformation systems and a series of experiments will be performed including temporal and spatial expression patterns, subcellular localization, transcriptome sequencing and metabolomic profiling, which may provide theoretical reference to breeding new varieties of rice resistance to blight bacterial.

白叶枯病是危害水稻产量的三大病害之一，新型抗病基因的挖掘与利用对于水稻抗病新品种的培育意义重大。本研究中，用EMS诱变处理高感白叶枯病恢复系广恢3550（R3550），筛选到一份功能获得性抗白叶枯突变体T1247，接种白叶枯病菌后，其病斑长度与野生型有显著差异。遗传分析显示该抗病突变性状由一对显性核基因控制，经BSA-Seq得到候选基因，位于第11染色体长臂，为一个新基因，暂命名为Xa45。不同于经典的抗病基因，Xa45不含LRRs序列区，是一个非典型抗病基因。又因T1247的各项农艺性状与R3550无显著差异，且R3550为大面积推广应用的高产恢复系，所以该抗病突变体及其显性突变基因在抗性育种中具有良好的应用潜力。本项目拟在前期研究基础上，进行转基因验证，并通过时空表达特征分析、亚细胞定位、转录组测序及代谢组学分析等手段探索其抗病机理，为培育新的抗白叶枯水稻品种提供理论参考。

白叶枯病菌是极具破坏力的一种病原微生物，在水稻大田生产中会引起严重的减产。通过遗传变异获取新突变的方法是在植物中导入新抗性基因的最有效方法之一。我们利用EMS诱变处理高感白叶枯病恢复系广恢3550（R3550），筛选到一份功能获得性抗白叶枯突变体T1247，接种白叶枯病菌后，其病斑长度与野生型有显著差异。因此，为了有效利用这一珍贵的抗性资源，我们通过基因组混池测序技术（BSA）结合转录组测序分析技术来挖掘T1247突变体的白叶枯病抗性遗传机理。通过BSA混池测序与转录组分析，对高抗白叶枯病突变体T1247进行了精细定位，将其定位到水稻11号染色体0.45Mb的区间内，包含33个基因和4个差异表达基因。其中三个基因响应白叶枯菌接种（OsR498G1120557200, OsR498G1120555700, and OsR498G1120563600）。同时，转录组测试结果揭示了其余37个与白叶枯病抗性相关的基因，且他们的调控途径不同。本研究为白叶枯菌相关QTL的有关研究提供了更多重要线索，并揭示了数个可供验证的候选基因，能够为培育抗白叶枯病新品种提供重要基因资源的同时，也为白叶枯病的抗病机理研究提供理论支撑。