稻黄单胞菌多样性的tale基因调控水稻抗（感）病性的机理与利用基础

Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc) are two pathovars of X. oryzae, causing bacterial blight (BB) and bacterial leaf streak (BLS) in rice, respectively. Regional and spasmodical occurrence of BB and BLS in rice growing areas in China is particularly due to the lost of resistance (R) which is overcame by newly evolved transcriptional activator-like effectors (tale) from the pathogens. Being coevolved with rice, Xoo and Xoc possess about 20 tale genes. The main differences among tale genes are the repeat numbers of a 102 bp repeat unit and, correspondingly, the repeat-variable diresidues (RVDs) at the 12th and 13th positions of the coding region. Each RVD, binding one pair of a nucleotide, enables one TALE protein to specifically recognize a DNA sequence with a promoter of an R or susceptibility (S) gene in rice that manipulate rice resistance or susceptibility to BB or BLS. To decipher tale-R (S) relationships between the pathogens and rice, we propose to analize tale diversities of different Xoo and Xoc strains or races collected from different rice growing areas, to investigate whether there are any interferences among tale genes for plant defense by using a strain without any tale genes; and to identify unknown targets (R or S genes) of some TALEs in rice by TALE coding prediction, TALE-promoter sequence hybridization and differential expression profiles between susceptible and resistant cultivars triggered by a tale gene. The revealed relationships between tale and R or S genes and identified unknown R or S genes will be of importance not only in understanding molecular mechanisms of rice-X. oryzae pathosystems, but also in rice resistant breeding and cultivar distribution avoiding pathogen infection.

白叶枯病菌(Xoo)和条斑病菌(Xoc)是稻黄单胞菌下两个致病变种，分别引起白叶枯病(BB)和条斑病(BLS)。BB和BLS在我国水稻产区区域性和间歇性成灾，主因是水稻中抗BB或BLS的抗病基因(R)被稻黄单胞菌中新进化的转录激活因子(tale)克服所致。与水稻协同进化，Xoo和Xoc中存在近20个tale基因。tale基因间的差异主要是102 bp重复单元的重复数以及编码第12和13位的氨基酸变异上，这2个位点的氨基酸可以结合特定的核苷酸从而每个TALE蛋白可以识别水稻中特定的 DNA序列以操控水稻的抗病性或感病性(S)。本项目拟对不同地域来源的tale基因进行多样性分析；利用已敲除全部tale基因的菌株分析tale基因间相互作用；应用密码计算、蛋白质与DNA互作以及水稻抗感表达谱分析和辅助F2群体，解析和分离tale对应水稻中未知R或S基因，揭示tale操控水稻抗（感）病性的分子机理。

白叶枯病菌(Xoo)和条斑病菌(Xoc)是稻黄单胞菌种下的两个致病变种，分别引起白叶枯病(BB)和条斑病(BLS)。BB和BLS在我国水稻产区区域性和间歇性成灾，主因是水稻中抗BB或BLS的抗病基因(R)被稻黄单胞菌中新进化的转录激活因子(tale)克服所致。本项目分离获得了我国不同水稻产区来源的Xoo菌株165株和Xoc菌株65株，根据tale基因大小和数量，将我国Xoo菌系划分为18个tale基因型，将Xoc菌系划分为14个基因型。抗病性检测发现，现有水稻材料不存在对条斑病的免疫性，含有xa5、Xa7和Xa23的水稻材料广谱抗白叶枯病菌，Xa4、Xa21和xa13抗性逐渐丧失。监控发现了可克服Xa23抗性的Xoo菌株，主要原因是该菌株不含有avrXa23基因。分离获得了50多个tale基因，发现Xoc来源的tal7和tal2g可分别抑制avrXa7-Xa7和 avrXa10-Xa10介导的ETI抗性，原因是tal7和tal2g分别作用水稻的感病基因。研究还发现，稻黄单胞菌中的iTALE基因可克服Xa1抗性，任何典型结构的TALE蛋白均能激活Xa1抗性。含Xa1的水稻抗不含有iTALE基因的稻黄单胞菌。研究还发现了Xa1的等位基因。3个感病基因修饰后的水稻，仍然有极少数Xoo菌株可克服其抗性，原因是病菌中存在变异的tale基因以及水稻中S基因位点变异所致。本项目另一重要成果是，稻黄单胞菌的TALE蛋白可招募水稻OsTFIIAγ1和OsTFIIAγ5，推测形成转录复合体，保证TALE蛋白的靶标基因转录表达。当OsTFIIAγ1和OsTFIIAγ5基因均突变后，水稻表现为更广谱抗性。这些处于领跑状态的研究结果，不仅对监控水稻生产上稻黄单胞菌的毒性组成以及有效培育和布局水稻抗性品种具有指导意义，而且科学回答了稻黄单胞菌如何利用TALE蛋白调控水稻抗病性和感病性的机理。