Involvement of MAK-1 and MAK-2 MAP kinases in cell wall integrity in <i>Neurospora crassa</i>

Among three MAPK disruptants of <i>Neurospora crassa</i>, <i>Δmak</i>-<i>1</i> was sensitive and <i>Δmak</i>-<i>2</i> was hypersensitive to micafungin, a beta-1,3-glucan synthase inhibitor, than the wild-type or <i>Δos</i>-<i>2</i> strains. We identified six micafungin-inducible genes that are involved in cell wall integrity (CWI) and found that MAK-1 regulated the transcription of non-anchored cell wall protein gene, <i>ncw</i>-<i>1,</i> and the beta-1,3-endoglucanase gene, <i>bgt</i>-<i>2</i>, whereas MAK-2 controlled the expression of the glycosylhydrolase-like protein gene, <i>gh76</i>-<i>5</i>, and the C4-dicarboxylate transporter gene, <i>tdt</i>-<i>1</i>. Western blotting analysis revealed that, in the wild-type strain, MAK-1 was constitutively phosphorylated from conidial germination to hyphal development. In contrast, the phosphorylation of MAK-2 was growth phase-dependent, and micafungin induced the phosphorylation of unphosphorylated MAK-2. It should be noted that the phosphorylation of MAK-1 was virtually abolished in the <i>Δmak</i>-<i>2</i> strain, but was significantly induced by micafungin, suggesting functional cross talk between MAK-1 and MAK-2 signalling pathway in CWI. Both MAP kinases, MAK-1 and MAK-2, are activated by micafungin, and upregulate the expression of cell wall-related genes.