水稻条斑病菌克服水稻白叶枯病抗性的机理研究

Bacterial leaf streak (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc) occurs more severely than bacterial leaf blight (BLB) by X. oryzae pv. oryzae (Xoo) in rice in south China and BLB resistant rice cultivars are not resistant to BLS. Accumulated evidence demonstrates that the resistance and susceptibility are activated by transcriptional activator-like effectors (TALEs) which bind to TALE-binding elements (EBEs) in the promoter regions of either resistance (R)or susceptible (S) genes. We previously found that TAL6 and TAL9 from Xoc suppress plant defense mediated by AvrXa7-Xa7 and AvrXa10-Xa10 interactions, respectively, putatively implying that TAL6 and TAL9 bind the EBEs of unknown S gene to repress the AvrXa7-Xa7 and AvrXa10-Xa10 defense. In this proposal, we are going: to isolate TAL6- or TAL9-targeted S gene in rice and to reveal the functions of these S genes for BLS development by several approaches including to RNA-seq technology, TALE-target computational prediction, designing dTALE, syntherizing TALENs for modification in EBEs of S genes; to compare the differences in signal trasduction between the occurrence of BLS led by TAL6 and TAL9 and the suppression of BLB by TAL6 and TAL9, respectively, either in Xoo or in Xoc backgrouds which contain AvrXa7-TAL6 and AvrXa10-TAL9 combinations. Through the suggested project, we expect to understand the mechanisms how Xoc overcomes BLB resistance that will improve our strategies in BLS resistance breeding.

我国南方稻区条斑病(BLS)重于白叶枯病(BLB),抗BLB水稻不抗BLS.条斑病菌(Xoc)和白叶枯病菌(Xoo)均利用转录类因子(transcriptional activator-like effectors,TALEs)结合抗病(R)和感病(S)基因的EBE(TALE-binding element)从而激活水稻抗感病性.我们发现,Xoc的TAL6和TAL9可分别抑制AvrXa7-Xa7和AvrXa10-Xa10抗性,推测TAL6和TAL9结合未知S基因的EBE从而抑制BLB抗性.我们拟通过RNA-seq、计算生物学、dTALE和TALEN等途径,鉴别TAL6和TAL9对应的S基因和其功能；利用avrXa7-tal6和avrXa10-tal9组合,在Xoc和Xoo背景下比较BLB抗性被抑制和BLS感病性被激活的信号传导异同,揭示Xoc克服BLB抗性机理，为培育BLS抗性水稻奠定基础

我国南方水稻产区条斑病(BLS)重于白叶枯病(BLB)。条斑病菌(Xoc)和白叶枯病菌(Xoo)均利用转录类因子(TALEs)结合抗病(R)和感病(S)基因的启动子从而激活水稻抗感病性。本研究发现，Xoc的TAL6（TAL7）和TAL9可分别抑制AvrXa7-Xa7和AvrXa10-Xa10抗性，推测TAL7和TAL9结合未知S基因的EBE从而抑制BLB抗性。通过转录组学、GUS报道法、EMSA检测和dTALE诱导等途径分析，发现水稻条斑病菌Tal7蛋白在水稻中的靶标基因为Os09g29100。基因编辑获得的Os09g29100修饰水稻，抗含有tal7的Xoc侵染，但在TAL7作用下不能抑制AvrXa7-Xa7抗性，说明Os09g29100是水稻条斑病菌的感病基因。同样策略，获得了TAL9在水稻中的靶标基因BGIOSIBCE003431，相应的基因编辑水稻，抗含有Tal9基因的Xoc侵染，但在TAL9作用下不能抑制AvrXa10-Xa10抗性。鉴于依赖于RAN聚合酶PolII的水稻转录因子TFIIA的γ亚基是OsTFIIAγ5(Xa5)或OsTFIIAγ1，而Xa5的39位氨基酸(V)突变为（E）时，则xa5水稻抗BLB。我们推测稻黄单胞菌可能通过TALE蛋白招募水稻OsTFIIAγ1 和 OsTFIIAγ5形成复合体，从而有利于TALE的标靶基因表达。为此，我们在xa5背景下突变了OsTFIIAγ1，发现OsTFIIAγ1突变后对BLS的抗性强于xa5水稻。BiFC和MST试验发现，TALE蛋白可与OsTFIIAγ1或 X5或xa5结合并在细胞核中定位，TALE蛋白与OsTFIIAγ1和X5互作的亲和力相似，并远高于TALE蛋白与xa5互作的亲和力。这说明OsTFIIAγ1和OsTFIIAγ5双突变的水稻，可广谱抗BLS。