MoWsc1, MoWsc2, and MoMid2 recognize host surface signals and regulate appressorium-mediated infection by <i>Magnaporthe oryzae</i>

Cell wall integrity (CWI) sensors are crucial upstream components of the major pathway regulating cell wall biosynthesis in fungi. However, little is known about the biological functions of CWI sensors in phytopathogenic fungi. Magnaporthe oryzae has 3 putative CWI sensors, MoWsc1, MoWsc2, and MoMid2. Here, we constructed knockout mutants for these 3 CWI sensor genes in M. oryzae, generating a total of 7 mutants. Whereas the pathogenicity of single-knockout mutant strains was not significantly lower, ΔMowsc2 ΔMomid2 and ΔMowsc1 ΔMowsc2 ΔMomid2 displayed significantly lower virulence than the wild-type strain. These 2 mutants were defective in forming appressoria on artificial hydrophobic surfaces and plant surfaces. Abnormal mitosis and autophagy also occurred in these 2 mutants during appressorium formation. Induction of appressorium formation by providing hydrophobic surfaces or exogenous signals revealed that MoWsc1 and MoWsc2 mainly participate in the recognition of hydrophobicity. Meanwhile, binding assays suggested that MoWsc2 and MoMid2 are mainly involved in the recognition of various rice (Oryza sativa) surface substances including 1,16-hexadecanediol, cis-9-octadecen-1-ol, 1-octacosanol, and 1-triacontanol. Furthermore, defects in appressorium penetration and invasive growth were also major causes of compromised virulence in mutants. Although the deletion of individual genes had a small impact on pathogenicity, we found that MoWsc1, MoWsc2, and MoMid2 proteins play independent roles in growth, sporulation, and stress responses, especially MoWsc2. Overall, CWI sensors are critical for vegetative growth, conidiation, CWI, and pathogenicity. While MoWsc1, MoWsc2, and MoMid2 have overlapping functions, MoWsc2 is key for regulating appressorium formation.