College of Plant Protection, Hainan University, Haikou 570228, China; Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pests (Hainan University), Ministry of Education, Haikou 570228, China.
College of Plant Protection, Hainan University, Haikou 570228, China; Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pests (Hainan University), Ministry of Education, Haikou 570228, China.
Microbiol Res. 2021 Jan;242:126599. doi: 10.1016/j.micres.2020.126599. Epub 2020 Sep 24.
Pathogens secrete effectors to establish a successful interaction with their host. It is well understood that plant pathogens recruit classically secreted chorismate mutase (Cmu) as an effector to disrupt plant salicylic acid (SA) synthesis. However, the identity and function of the Cmu effector from powdery mildew fungi remain unknown. Here, we identified a novel secreted Cmu effector, EqCmu, from rubber (Hevea brasiliensis Muell) powdery mildew fungus (Erysiphe quercicola). Unlike the classically secreted Cmu, EqCmu lack signal peptide, and exhibited characteristics of non-classically secreted proteins. EqCmu could fully complement a Saccharomyces cerevisiae ScAro7 mutant that was deficient in the synthesis of phenylalanine and tyrosine. In addition, transient expression of EqCmu could promote infection by Phytophthora capsici and reduce the levels of SA and the mRNA of PR1 gene in Nicotiana benthamiana in response to P. capsici infection, while confocal observations showed that EqCmu was localized within the cytoplasm and nucleus of transfected N. benthamiana leaf cells. These non-homologous systems assays provide evidences that EqCmu may serve as a "moonlighting" protein, which is not only a key enzyme in the synthesis of phenylalanine and tyrosine within fungal cells, but also has the function of regulating plant SA synthesis within plant cells. This is the first study to identify and functionally validate a candidate effector from E. quercicola. Overall, the non-classical secretion pathway is a novel mechanism for powdery mildew fungal effectors secretion and might play an important role in host-pathogen interactions.
病原体分泌效应子与宿主建立成功的相互作用。人们已经充分了解到，植物病原体招募经典分泌的分支酸变位酶（Cmu）作为一种效应子来破坏植物水杨酸（SA）的合成。然而，白粉病真菌的 Cmu 效应子的身份和功能仍然未知。在这里，我们从橡胶（Hevea brasiliensis Muell）白粉病真菌（Erysiphe quercicola）中鉴定出一种新型分泌的 Cmu 效应子 EqCmu。与经典分泌的 Cmu 不同，EqCmu 缺乏信号肽，并表现出非经典分泌蛋白的特征。EqCmu 可以完全补充 Saccharomyces cerevisiae ScAro7 突变体，该突变体缺乏苯丙氨酸和酪氨酸的合成。此外，瞬时表达 EqCmu 可以促进辣椒疫霉的感染，并降低 Nicotiana benthamiana 中 SA 和 PR1 基因 mRNA 的水平，以响应 P. capsici 的感染，而共聚焦观察表明 EqCmu 定位于转染的 N. benthamiana 叶细胞的细胞质和核内。这些非同源系统测定提供了证据表明 EqCmu 可能作为一种“多功能”蛋白，它不仅是真菌细胞中苯丙氨酸和酪氨酸合成的关键酶，而且还具有调节植物细胞中 SA 合成的功能。这是首次从 E. quercicola 中鉴定和功能验证候选效应子的研究。总的来说，非经典分泌途径是白粉病真菌效应子分泌的一种新机制，可能在宿主-病原体相互作用中发挥重要作用。
