Ji Zhi-Yuan, Xiong Li, Zou Li-Fang, Li Yu-Rong, Ma Wen-Xiu, Liu Liang, Zakria Muhammad, Ji Guang-Hai, Chen Gong-You
Mol Plant Microbe Interact. 2014 Sep;27(9):983-95. doi: 10.1094/MPMI-09-13-0279-R.
The closely related plant pathogens Xanthomonas oryzae pv. oryzicola and X. oryzae pv. oryzae cause bacterial leaf streak (BLS) and bacterial leaf blight (BLB), respectively, in rice. Unlike X. oryzae pv. oryzae, endogenous avirulence-resistance (avr-R) gene interactions have not been identified in the X. oryzae pv. oryzicola-rice pathosystem, though both X. oryzae pv. oryzicola and X. oryzae pv. oryzae possess transcriptional activator-like effectors (TALE), which are known to modulate R or S genes in rice. In this report, avrXa7, avrXa10, and avrXa27 from X. oryzae pv. oryzae were transferred into YNB0-17 and RS105, hypovirulent and hypervirulent strains, respectively, of X. oryzae pv. oryzicola. When YNB0-17 containing avrXa7, avrXa10, or avrXa27 was inoculated to rice, hypersensitive responses (HR) were elicited in rice cultivars containing the R genes Xa7, Xa10, and Xa27, respectively. By contrast, RS105 expressing avrXa27 elicited an HR in a rice cultivar containing Xa27 but the expression of avrXa7 and avrXa10 in RS105 did not result in HR in rice cultivars containing Xa7 and Xa10, correspondingly. Southern blot analysis demonstrated that YNB0-17 possesses only approximately nine putative tale genes, whereas the hypervirulent RS105 contains at least 20. Although YNB0-17 contains an intact type III secretion system (T3SS), its genome is lacking the T3SS effector genes avrRxo1 and xopO, which are present in RS105. The introduction of avrRxo1 and xopO into YNB0-17 did not suppress avrXa7- or avrXa10-triggered immunity in rice. However, the transference of individual tale genes from RS105 into YNB0-17 led to the identification of tal6 and tal11a that suppressed avrXa7-Xa7-mediated defense. Thus, YNB0-17 may be a useful recipient for discovering such suppressors. This is the first report that co-evolutionally generated tale genes in X. oryzae pv. oryzicola suppress gene-for-gene defense against BLB, which may explain the lack of BLS-resistant cultivars.
密切相关的植物病原菌水稻条斑病菌（Xanthomonas oryzae pv. oryzicola）和水稻白叶枯病菌（X. oryzae pv. oryzae）分别在水稻中引起细菌性条斑病（BLS）和细菌性叶枯病（BLB）。与水稻白叶枯病菌不同，在水稻条斑病菌 - 水稻病理系统中尚未鉴定出内源性无毒力 - 抗性（avr - R）基因相互作用，尽管水稻条斑病菌和水稻白叶枯病菌都拥有转录激活样效应因子（TALE），已知这些效应因子可调节水稻中的R或S基因。在本报告中，将来自水稻白叶枯病菌的avrXa7、avrXa10和avrXa27分别转入水稻条斑病菌的弱毒菌株YNB0 - 17和强毒菌株RS105中。当将含有avrXa7、avrXa10或avrXa27的YNB0 - 17接种到水稻上时，分别在含有R基因Xa7、Xa10和Xa27的水稻品种中引发了过敏反应（HR）。相比之下，表达avrXa27的RS105在含有Xa27的水稻品种中引发了HR，但RS105中avrXa7和avrXa10的表达在含有Xa7和Xa10的水稻品种中并未相应地引发HR。Southern印迹分析表明，YNB0 - 17仅拥有大约9个推定的tale基因，而强毒的RS105至少含有20个。尽管YNB0 - 17含有完整的III型分泌系统（T3SS），但其基因组缺少RS105中存在的T3SS效应因子基因avrRxo1和xopO。将avrRxo1和xopO引入YNB0 - 17并未抑制水稻中avrXa7或avrXa10触发的免疫反应。然而，将RS105中的单个tale基因转移到YNB0 - 17中导致鉴定出抑制avrXa7 - Xa7介导的防御的tal6和tal11a。因此，YNB0 - 17可能是发现此类抑制因子的有用受体。这是第一份关于水稻条斑病菌中共同进化产生的tale基因抑制针对白叶枯病的基因对基因防御的报告，这可能解释了缺乏抗条斑病品种的原因。
