Mitogen-activated protein kinase (MAPK) cascades are key signaling modules controlling development and virulence in fungal pathogens. Down-regulation of MAPK activity by protein phosphatases provides a critical layer of control during desensitization or adaptation to stimuli. In Saccharomyces cerevisiae, the dual-specificity phosphatase Msg5 dephosphorylates target threonine and tyrosine residues in the two MAPKs Mpk1 and Fus3, which regulate the cell wall integrity (CWI) and pheromone responses, respectively. Here we studied the role of the Msg5 ortholog in Fusarium oxysporum, a soilborne phytopathogen that infects host plants through the roots to cause vascular wilt and plant death. F. oxysporum mutants lacking Msg5 showed constitutively high levels of Mpk1 phosphorylation and increased sensitivity to the cell wall targeting compound Calcofluor White. Moreover, these mutants displayed reduced colony growth and conidiation. Importantly, msg5Δ mutants were impaired in hyphal chemotropism towards host plant roots and in virulence on tomato plants. These results reveal a key role of Msg5 in regulation of the CWI MAPK cascade of F. oxysporum as well as in infection-related signaling of this important fungal pathogen.

丝裂原活化蛋白激酶 (MAPK) 级联是控制真菌病原体发育和毒力的关键信号模块。蛋白磷酸酶对 MAPK 活性的下调在脱敏或适应刺激过程中提供了一个关键的控制层。在酿酒酵母中，双特异性磷酸酶 Msg5 去磷酸化靶向两个 MAPK Mpk1 和 Fus3 中的苏氨酸和酪氨酸残基，它们分别调节细胞壁完整性 (CWI) 和信息素反应。在这里，我们研究了 Msg5 直向同源物在尖孢镰刀菌中的作用，尖孢镰刀菌是一种土传植物病原体，通过根部感染寄主植物，导致维管枯萎和植物死亡。尖孢镰刀菌缺乏 Msg5 的突变体表现出组成性高水平的 Mpk1 磷酸化和对细胞壁靶向化合物 Calcofluor White 的敏感性增加。此外，这些突变体表现出减少的菌落生长和分生孢子。重要的是，msg5 Δ 突变体在对宿主植物根部的菌丝趋化性和对番茄植物的毒力方面受损。这些结果揭示了 Msg5 在调节尖孢镰刀菌的 CWI MAPK 级联以及这种重要真菌病原体的感染相关信号传导中的关键作用。