Institute for Integrative Biology of the Cell (I2BC), Université Paris-Saclay, CEA, CNRS, Gif-sur-Yvette, France.
Laboratory of Molecular Plant Pathology, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand.
PLoS Pathog. 2022 Jul 6;18(7):e1010664. doi: 10.1371/journal.ppat.1010664. eCollection 2022 Jul.
Recognition of a pathogen avirulence (AVR) effector protein by a cognate plant resistance (R) protein triggers a set of immune responses that render the plant resistant. Pathogens can escape this so-called Effector-Triggered Immunity (ETI) by different mechanisms including the deletion or loss-of-function mutation of the AVR gene, the incorporation of point mutations that allow recognition to be evaded while maintaining virulence function, and the acquisition of new effectors that suppress AVR recognition. The Dothideomycete Leptosphaeria maculans, causal agent of oilseed rape stem canker, is one of the few fungal pathogens where suppression of ETI by an AVR effector has been demonstrated. Indeed, AvrLm4-7 suppresses Rlm3- and Rlm9-mediated resistance triggered by AvrLm3 and AvrLm5-9, respectively. The presence of AvrLm4-7 does not impede AvrLm3 and AvrLm5-9 expression, and the three AVR proteins do not appear to physically interact. To decipher the epistatic interaction between these L. maculans AVR effectors, we determined the crystal structure of AvrLm5-9 and obtained a 3D model of AvrLm3, based on the crystal structure of Ecp11-1, a homologous AVR effector candidate from Fulvia fulva. Despite a lack of sequence similarity, AvrLm5-9 and AvrLm3 are structural analogues of AvrLm4-7 (structure previously characterized). Structure-informed sequence database searches identified a larger number of putative structural analogues among L. maculans effector candidates, including the AVR effector AvrLmS-Lep2, all produced during the early stages of oilseed rape infection, as well as among effector candidates from other phytopathogenic fungi. These structural analogues are named LARS (for Leptosphaeria AviRulence and Suppressing) effectors. Remarkably, transformants of L. maculans expressing one of these structural analogues, Ecp11-1, triggered oilseed rape immunity in several genotypes carrying Rlm3. Furthermore, this resistance could be suppressed by AvrLm4-7. These results suggest that Ecp11-1 shares a common activity with AvrLm3 within the host plant which is detected by Rlm3, or that the Ecp11-1 structure is sufficiently close to that of AvrLm3 to be recognized by Rlm3.
病原菌无毒（AVR）效应蛋白被同源植物抗性（R）蛋白识别，触发一系列免疫反应，使植物具有抗性。病原体可以通过多种机制逃避这种所谓的效应子触发的免疫（ETI），包括 AVR 基因的缺失或功能丧失突变、引入允许逃避识别的点突变而保持毒性功能，以及获得抑制 AVR 识别的新效应子。长柄壳属的长柄壳菌，是少数几种已证明其 AVR 效应子抑制 ETI 的真菌病原体之一。事实上，AvrLm4-7 分别抑制由 AvrLm3 和 AvrLm5-9 触发的 Rlm3-和 Rlm9-介导的抗性。AvrLm4-7 的存在并不妨碍 AvrLm3 和 AvrLm5-9 的表达，并且这三个 AVR 蛋白似乎没有物理相互作用。为了解析这些长柄壳菌 AVR 效应子之间的上位互作，我们测定了 AvrLm5-9 的晶体结构，并基于 Fulvia fulva 同源 AVR 效应子候选物 Ecp11-1 的晶体结构获得了 AvrLm3 的 3D 模型。尽管缺乏序列相似性，但 AvrLm5-9 和 AvrLm3 是 AvrLm4-7 的结构类似物（以前表征的结构）。基于结构的序列数据库搜索在长柄壳菌效应子候选物中鉴定出了更多的假定结构类似物，包括在油菜感染早期产生的 AVR 效应子 AvrLmS-Lep2，以及其他植物病原真菌的效应子候选物。这些结构类似物被命名为 LARS（代表长柄壳菌 AviRulence 和 Suppressing）效应子。值得注意的是，表达这些结构类似物之一 Ecp11-1 的长柄壳菌转化体在携带 Rlm3 的几种基因型中触发了油菜的免疫反应。此外，这种抗性可以被 AvrLm4-7 抑制。这些结果表明，Ecp11-1 在宿主植物中与 AvrLm3 具有共同的活性，被 Rlm3 检测到，或者 Ecp11-1 的结构与 AvrLm3 足够接近，被 Rlm3 识别。
