XA13新互作蛋白OsHMGB1介导的负调控水稻免疫机制解析

稻黄单胞杆菌水稻变种携带的一类三型分泌蛋白扮演植物转录因子的角色，可进入细胞核并直接作用于水稻靶基因启动子特殊位点调控目标基因的表达。其中一类靶基因编码SWEET细胞膜蛋白（如XA13），被认为是主要的感病必需蛋白。本研究围绕解析XA13介导的感病机制，从新鉴定的XA13羧基端互作蛋白OsHMGB1入手，通过遗传学、细胞生物学等手段验证OsHMGB1基因参与Xa13介导的感病性。同时，比较OsHMGB1与SWEET蛋白第三亚型家族成员间的相互作用，提出并规划验证新假说：XA13等多个SWEET蛋白第三亚型家族成员通过与OsHMGB1的直接互作抑制水稻基础免疫。进而对OsHMGB1参与的转录调控及互作蛋白的分析，解析OsHMGB1如何介入SWEET蛋白调控的水稻白叶枯病的感病性。同时，也将xa13等隐性抗病基因从小种特异性抗性拓宽到调控因子介导的宽抗谱抗性，为抗白叶枯病育种提供改良新目标。

Xanthomonas oryzae pv. oryzae (Xoo), causing the bacterial blight disease in rice, carry large numbers of transcription activator-like effectors which belong to a subfamily of type III secretion proteins. It could be delivered into rice nuclei to mimic the plant transcription factor that directly binds to the promoter region and activates the expression of the target gene. Several TAL’s targets are necessary for susceptibility which encode plasma membrane proteins of SWEET family that mediate the sucrose and glucose efflux from the phloem parenchyma cells to the apoplast to provide the nutrient for pathogen proliferation in rice. In this proposal, we aim to explore the mechanism of Xa13-mediated susceptibility. Our current data was shown that the carboxyl terminus of XA13 protein is required for fully susceptibility to PXO99 carrying the cognate TAL effector PthXo1. And the OsHMGB1 was identified to interact with the carboxyl terminus of XA13 and to negatively regulate the rice immunity.We will validate the function of OsHMGB1 involved into Xa13-mediated susceptibility with the tools of genetic and cytobiology. Then we plan to test the interactions between OsHMGB1 and other clade III subfamily members of OsSWEET. These will support the proposed hypothesis that several members of clade III subfamily of OsSWEETs negatively regulate the plant immunity by interacting with OsHMGB1. Finally, to answer the question of how to negatively regulate the rice immunity for OsHMGB1, we try to identify the signal component downstream the OsHMGB1 by RNA-seq and yeast two hybridization. The results will enlarge to broad spectrum resistant to Xoo strains by modulating the expression of OsHMGB1 than by modifying those race-specific recessive resistance genes as xa13, xa25 etc. These will also provide new resources for genetic improvement of bacterial blight resistance.