作为一种破坏性的植物病原体,致病疫霉分泌多种进入宿主的RxLR效应子以促进感染。一个关键的RxLR效应器,PiAvr3b,不仅诱导效应子触发免疫(ETI),它与马铃薯抗性蛋白StR3b有关,但也抑制病原体相关分子模式(PAMP)触发的免疫(PTI)。迄今为止,这种双重活动的分子基础仍然未知。基于全球致病假单胞菌分离株的系统发育分析,我们发现了两种PiAvr3b同工型,它们相差三个氨基酸。尽管有这种序列变异,这两种同工型在激活StR3b介导的超敏反应(HR)和抑制由三种PAMPs诱导的坏死(PiNpp,PiINF1和PsXeg1)和RxLR效应器(Pi10232)。使用联合诱变方法,我们发现PiAvr3b的双重活性紧密相连,并由C末端的88个氨基酸决定。我们进一步确定PiAvr3b的W60或E134残基对于触发StR3b相关的HR和抑制PiNpp和Pi10232相关的坏死是必不可少的。而S99残基部分有助于PTI抑制。此外,PiAvr3b的核定位需要刺激HR和抑制PTI,但不能抑制Pi10232相关的细胞死亡.我们的研究表明,PiAvr3b抑制了不同亚细胞位置的植物免疫反应,并提供了一个例子,其中RxLR效应子的单个氨基酸将ETI诱导和细胞死亡抑制联系起来。
As a destructive plant pathogen, Phytophthora infestans secretes diverse host-entering RxLR effectors to facilitate infection. One critical RxLR effector, PiAvr3b, not only induces effector-triggered immunity (ETI), which is associated with the potato resistance protein StR3b, but also suppresses pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI). To date, the molecular basis underlying such dual activities remains unknown. Based on phylogenetic analysis of global P. infestans isolates, we found two PiAvr3b isoforms that differ by three amino acids. Despite this sequence variation, the two isoforms retain the same properties in activating the StR3b-mediated hypersensitive response (HR) and inhibiting necrosis induced by three PAMPs (PiNpp, PiINF1, and PsXeg1) and an RxLR effector (Pi10232). Using a combined mutagenesis approach, we found that the dual activities of PiAvr3b were tightly linked and determined by 88 amino acids at the C-terminus. We further determined that either the W60 or the E134 residue of PiAvr3b was essential for triggering StR3b-associated HR and inhibiting PiNpp- and Pi10232-associated necrosis, while the S99 residue partially contributed to PTI suppression. Additionally, nuclear localization of PiAvr3b was required to stimulate HR and suppress PTI, but not to inhibit Pi10232-associated cell death. Our study revealed that PiAvr3b suppresses the plant immune response at different subcellular locations and provides an example in which a single amino acid of an RxLR effector links ETI induction and cell death suppression.