Dual-specificity protein phosphatase Msg5 controls cell wall integrity and virulence in Fusarium oxysporum

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 Mpk2 phosphorylation and increased sensitivity to the cell wall targeting compound Calcofluor White. Moreover, these mutants displayed reduced colony growth and conidiation. Importantly, msg50 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.