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.

病原体分泌效应子以与其宿主建立成功的相互作用。众所周知，植物病原体募集经典分泌的分支酸盐变位酶（Cmu）作为破坏植物水杨酸（SA）合成的效应子。然而，来自白粉病真菌的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）中鉴定了一种新型的分泌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可以完全补充酿酒酵母ScAro7苯丙氨酸和酪氨酸合成不足的突变体。此外，EqCmu的瞬时表达可通过促进感染辣椒疫霉和降低SA的水平和mRNA中的PR1在基因本塞姆氏烟草响应于辣椒疫霉感染，而共焦观察表明EqCmu是细胞质和细胞核内的局部转染的本氏烟草叶细胞。这些非同源系统分析提供了证据，证明EqCmu可以充当“月光”蛋白，不仅是真菌细胞内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内植物SA合成的功能。 。这是第一项鉴定和功能验证来自大肠杆菌的候选效应子的研究。总体而言，非经典的分泌途径是白粉病真菌效应子分泌的新机制，并且可能在宿主与病原体的相互作用中发挥重要作用。