MoEgh1 regulates sterol homeostasis and autophagy pathways in Magnaporthe oryzae

Abstract:

Ergosteryl-β-glucosidase (Egh1) catalyzes the hydrolysis of ergosteryl-β-glucoside for producing free ergosterol and glucose. This enzyme plays a crucial role in maintaining intracellular membrane lipid homeostasis and regulating the morphological stability of organelles, including vacuoles. However, the biological functions of this enzyme class in plant pathogenic fungi remain poorly understood.Objective To elucidate the role of MoEGH1, an Egh1 homolog in Magnaporthe oryzae, in appressorium development, sterol metabolism, autophagy regulation, and pathogenicity.Methods MoEGH1, homologous to yeast EGH1, was identified by sequence homology analysis. A deletion mutant ΔMoegh1 was constructed through targeted gene replacement. The biological functions of MoEgh1 were systematically examined through phenotypic characterization, genetic complementation, autophagic flux assays, and assessments of appressorium formation and turgor pressure.Results The deletion of MoEGH1 markedly impaired the growth, development, and pathogenicity of M. oryzae. ΔMoegh1 displayed significantly reduced radial growth and conidiation, an increased proportion of malformed conidia, a substantial decrease in appressorial turgor pressure, and defective appressorium formation. These developmental defects led to an almost complete loss of pathogenicity. Furthermore, compared with the wild-type strain, ΔMoegh1 demonstrated heightened sensitivity to rapamycin and sterol-targeting antifungal agents, including natamycin, amphotericin B, and itraconazole. Additionally, the mutant displayed abnormally elevated activity of the target of rapamycin (TOR) signaling pathway concomitant with reduced levels of autophagy.Conclusion MoEgh1 is essential for vegetative growth, conidiation, and appressorium formation in M. oryzae. MoEgh1 regulates the autophagy process and sterol homeostasis by modulating TOR activity, thereby playing a critical role in the pathogenicity of this fungus.