Tanaka Shigeyuki, Gollin Isabelle, Rössel Nicole, Kahmann Regine
Department of Organismic Interactions, Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Straße 10, D-35043, Marburg, Germany.
New Phytol. 2020 Jul;227(1):185-199. doi: 10.1111/nph.16508. Epub 2020 Mar 25.
The biotrophic fungus Ustilago maydis causes the smut disease of maize. The interaction with its host and induction of characteristic tumors are governed largely by secreted effectors whose function is mostly unknown. To identify effectors with a prominent role in virulence, we used RNA sequencing and found that the gene sta1 is upregulated during early stages of infection. We characterized Sta1 by comparative genomics, reverse genetics, protein localization, stress assays, and microscopy. sta1 mutants show a dramatic reduction of virulence and show altered colonization of tissue neighboring the vascular bundles. Functional orthologues of Sta1 are found in related smut pathogens infecting monocot and dicot plants. Sta1 is secreted by budding cells but is attached to the cell wall of filamentous hyphae. Upon constitutive expression of Sta1, fungal filaments become susceptible to Congo red, β-glucanase, and chitinase, suggesting that Sta1 alters the structure of the fungal cell wall. Constitutive or delayed expression of sta1 during plant colonization negatively impacts on virulence. Our results suggest that Sta1 is a novel kind of effector, which needs to modify the hyphal cell wall to allow hyphae to be accommodated in tissue next to the vascular bundles.
活体营养型真菌玉米黑粉菌可引发玉米的黑粉病。它与宿主的相互作用以及特征性肿瘤的诱导很大程度上受分泌效应子的调控，而这些效应子的功能大多未知。为了鉴定在毒力方面起重要作用的效应子，我们使用RNA测序，发现基因sta1在感染早期上调。我们通过比较基因组学、反向遗传学、蛋白质定位、胁迫试验和显微镜观察对Sta1进行了表征。sta1突变体的毒力显著降低，并且在维管束邻近组织中的定殖情况发生改变。在感染单子叶和双子叶植物的相关黑粉病菌中发现了Sta1的功能直系同源物。Sta1由出芽细胞分泌，但附着在丝状菌丝的细胞壁上。在组成型表达Sta1后，真菌丝状体对刚果红、β-葡聚糖酶和几丁质酶敏感，这表明Sta1改变了真菌细胞壁的结构。在植物定殖过程中组成型或延迟表达sta1会对毒力产生负面影响。我们的结果表明，Sta1是一种新型效应子，它需要修饰菌丝细胞壁，以使菌丝能够在维管束旁边的组织中存活。
