The Fungal Cell-Wall Integrity MAPK Cascade Is Crucial for Hyphal Network Formation and Maintenance of Restrictive Growth of Epichloe festucae in Symbiosis With Lolium perenne
The Fungal Cell-Wall Integrity MAPK Cascade Is Crucial for Hyphal Network Formation and Maintenance of Restrictive Growth of Epichloe festucae in Symbiosis With Lolium perenne
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DOI：
10.1094/mpmi-06-14-0183-r
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发表时间：
2015-01-01
影响因子：
3.5
通讯作者：
Scott, Barry
中科院分区：
文献类型：
--
作者：
Becker, Yvonne;Eaton, Carla J.;Scott, Barry
三叶草是一种共生共生体，系统地定殖在多年生黑麦草叶片的细胞间隙，形成一个高度结构化和相互连接的菌丝网络。在根癌农杆菌T-DNA正向遗传筛选中，我们鉴定了一个突变体TM 1066，该突变体具有严重的宿主互作表型，导致宿主发育迟缓和早衰。分子分析显示，导致这种表型的突变是在细胞壁完整性（CWI）丝裂原活化蛋白激酶激酶（MAPKK），mkkA。通过靶向缺失mkkA或下游mpkA激酶产生的突变体重现了观察到的TM 1066的表型。这两个突变体的菌丝细胞融合缺陷，形成菌丝内菌丝，有增强的分生孢子，并显示微循环分生孢子。透射电子显微镜和共聚焦显微镜分析表明，突变体菌丝比野生型更丰富的细胞间隙和定殖的维管束。菌丝分支未能融合，而是一个接一个地生长，形成卷曲的菌丝束。突变体菌丝与AF 488-WGA显示出增加的荧光，表明几丁质的可及性增加，细胞壁超微结构的变化支持的假设。这些结果表明，CWI MAPK信号通路是控制大肠杆菌间互惠共生相互作用的关键信号通路。festucae和L.多年生植物
Epichloe festucae is a mutualistic symbiont that systemically colonizes the intercellular spaces of Lolium perenne leaves to form a highly structured and interconnected hyphal network. In an Agrobacterium tumefaciens T-DNA forward genetic screen, we identified a mutant TM1066 that had a severe host interaction phenotype, causing stunting and premature senescence of the host. Molecular analysis revealed that the mutation responsible for this phenotype was in the cell-wall integrity (CWI) mitogen-activated protein kinase kinase (MAPKK), mkkA. Mutants generated by targeted deletion of the mkkA or the downstream mpkA kinase recapitulated the phenotypes observed for TM1066. Both mutants were defective in hyphal cell-cell fusion, formed intrahyphal hyphae, had enhanced conidiation, and showed microcyclic conidiation. Transmission electron microscopy and confocal microscopy analysis of leaf tissue showed that mutant hyphae were more abundant than the wild type in the intercellular spaces and colonized the vascular bundles. Hyphal branches failed to fuse but, instead, grew past one another to form bundles of convoluted hyphae. Mutant hyphae showed increased fluorescence with AF488-WGA, indicative of increased accessibility of chitin, a hypothesis supported by changes in the cell-wall ultrastructure. These results show that the CWI MAPK pathway is a key signaling pathway for controlling the mutualistic symbiotic interaction between E. festucae and L. perenne.