Zhang Xue, Liu Wende, Li Yang, Li Guotian, Xu Jin-Rong
Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA.
College of Plant Protection, Purdue-NWAFU Joint Research Center, Northwest A&F University, Yangling, Shaanxi 712100, China.
Environ Microbiol. 2017 Oct;19(10):4190-4204. doi: 10.1111/1462-2920.13884. Epub 2017 Aug 24.
The Pmk1 and Mps1 MAP kinases are essential for appressorium formation and plant infection in Magnaporthe oryzae. However, their exact roles during invasive growth are not clear because pmk1 and mps1 mutants are defective in penetration. To further characterize their functions after penetration, in this study we expressed the Pseudomonas syringae effector HopAI known to inactivate plant MAP kinases in M. oryzae. Constitutive expression of HopAI with the RP27 or TrpC promoter resulted in defects in hyphal growth, conidiation, appressorium penetration and pathogenicity, which is similar to the phenotype of the mps1 mutant. HopAI interacted strongly with Mps1 in vivo and expression of dominant active MKK2 partially suppressed the defects of P -HopAI transformants, which were significantly reduced in Mps1 phosphorylation. When the infection-specific MIR1 (Magnaporthe-infection-related gene-1) promoter was used to express HopAI, P -HopAI transformants were defective in the spreading of invasive hyphae and elicited strong defense responses in penetrated plant cells. Expression of HopAI in Fusarium graminearum also mainly affected the activation of Mgv1, an Mps1 orthologue. Taken together, our results showed that Mps1 is the major intracellular target of HopAI when it is overexpressed, and MAP kinase signalling is important for cell-to-cell movement of invasive hyphae in M. oryzae.
Pmk1和Mps1丝裂原活化蛋白激酶对于稻瘟病菌附着胞的形成和植物侵染至关重要。然而，它们在侵染性生长过程中的具体作用尚不清楚，因为pmk1和mps1突变体在穿透过程中存在缺陷。为了进一步阐明它们在穿透后的功能，在本研究中，我们在稻瘟病菌中表达了已知能使植物丝裂原活化蛋白激酶失活的丁香假单胞菌效应蛋白HopAI。用RP27或色氨酸合成酶启动子组成型表达HopAI会导致菌丝生长、产孢、附着胞穿透和致病性方面的缺陷，这与mps1突变体的表型相似。HopAI在体内与Mps1强烈相互作用，显性活性MKK2的表达部分抑制了P -HopAI转化体的缺陷，这些转化体中Mps1的磷酸化显著降低。当使用感染特异性的MIR1（稻瘟病菌感染相关基因-1）启动子来表达HopAI时，P -HopAI转化体在侵染菌丝的扩展方面存在缺陷，并在被穿透的植物细胞中引发强烈的防御反应。在禾谷镰刀菌中表达HopAI也主要影响Mps1的直系同源物Mgv1的激活。综上所述，我们的结果表明，当HopAI过表达时，Mps1是其主要的细胞内靶点，并且丝裂原活化蛋白激酶信号传导对于稻瘟病菌侵染菌丝的细胞间移动很重要。
