Eitas Timothy K, Nimchuk Zachary L, Dangl Jeffery L
Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599, USA.
Proc Natl Acad Sci U S A. 2008 Apr 29;105(17):6475-80. doi: 10.1073/pnas.0802157105. Epub 2008 Apr 18.
The type III effector protein encoded by avirulence gene B (AvrB) is delivered into plant cells by pathogenic strains of Pseudomonas syringae. There, it localizes to the plasma membrane and triggers immunity mediated by the Arabidopsis coiled-coil (CC)-nucleotide binding (NB)-leucine-rich repeat (LRR) disease resistance protein RPM1. The sequence unrelated type III effector avirulence protein encoded by avirulence gene Rpm1 (AvrRpm1) also activates RPM1. AvrB contributes to virulence after delivery from P. syringae in leaves of susceptible soybean plants, and AvrRpm1 does the same in Arabidopsis rpm1 plants. Conditional overexpression of AvrB in rpm1 plants results in leaf chlorosis. In a genetic screen for mutants that lack AvrB-dependent chlorosis in an rpm1 background, we isolated TAO1 (target of AvrB operation), which encodes a Toll-IL-1 receptor (TIR)-NB-LRR disease resistance protein. In rpm1 plants, TAO1 function results in the expression of the pathogenesis-related protein 1 (PR-1) gene, suggestive of a defense response. In RPM1 plants, TAO1 contributes to disease resistance in response to Pto (P. syringae pathovars tomato) DC3000(avrB), but not against Pto DC3000(avrRpm1). The tao1-5 mutant allele, a stop mutation in the LRR domain of TAO1, posttranscriptionally suppresses RPM1 accumulation. These data provide evidence of genetically separable disease resistance responses to AvrB and AvrRpm1 in Arabidopsis. AvrB activates both RPM1, a CC-NB-LRR protein, and TAO1, a TIR-NB-LRR protein. These NB-LRR proteins then act additively to generate a full disease resistance response to P. syringae expressing this type III effector.
无毒基因B(AvrB)编码的III型效应蛋白由丁香假单胞菌的致病菌株传递到植物细胞中。在植物细胞中,它定位于质膜,并触发由拟南芥卷曲螺旋(CC)-核苷酸结合(NB)-富含亮氨酸重复序列(LRR)抗病蛋白RPM1介导的免疫反应。无毒基因Rpm1(AvrRpm1)编码的与序列无关的III型效应无毒蛋白也能激活RPM1。AvrB从丁香假单胞菌传递到易感大豆植株叶片后有助于致病,AvrRpm1在拟南芥rpm1植株中也有同样作用。在rpm1植株中条件性过表达AvrB会导致叶片黄化。在一项针对在rpm1背景下缺乏AvrB依赖性黄化的突变体的遗传筛选中,我们分离出了TAO1(AvrB作用靶点),它编码一种Toll样白细胞介素-1受体(TIR)-NB-LRR抗病蛋白。在rpm1植株中,TAO1的功能导致病程相关蛋白1(PR-1)基因的表达,这表明存在防御反应。在RPM1植株中,TAO1有助于对丁香假单胞菌番茄致病变种(Pto)DC3000(avrB)产生抗病性,但对Pto DC3000(avrRpm1)没有作用。tao1-5突变等位基因是TAO1的LRR结构域中的一个终止突变,它在转录后抑制RPM1的积累。这些数据提供了拟南芥对AvrB和AvrRpm1的遗传上可分离的抗病反应的证据。AvrB既能激活CC-NB-LRR蛋白RPM1,也能激活TIR-NB-LRR蛋白TAO1。然后这些NB-LRR蛋白协同作用,对表达这种III型效应蛋白的丁香假单胞菌产生全面的抗病反应。