SNX-BAR protein StMvp1 is required for the endosomal sorting, melanin transport, and pathogenicity of Setosphaeria turcica

Abstract

The fungal pathogen Setosphaeria turcica causes northern corn leaf blight and relies on melanized appressoria for host invasion. SNX-BAR proteins are a subfamily of Sorting nexins (SNX), which regulate membrane trafficking, cargo sorting and membrane remodeling at the endosome. Previous studies have suggested that SNX-BARs play a critical role in growth, development and virulence of plant pathogens. However, its roles in S. turcica remain not fully understood. Here, we characterized the SNX-BAR protein StMvp1, a homolog of yeast Mvp1, in S. turcica and uncovered its critical role in melanin biosynthesis, autophagy, and pathogenicity. Deletion of StMvp1 impaired polarized growth, and appressorium development, significantly reducing pathogenicity on maize. StMvp1 located in endosomes and is necessary for endocytosis. Notably, ΔStMvp1 accumulated intracellular melanin due to the mislocalization of key synthases (StPKS18, StLac1, and StSCD3), which were trapped in punctate endosomal compartments. Meanwhile, ΔStMvp1 exhibited aberrant autophagosome formation and impaired autophagy-dependent appressorium maturation. Our study establishes StMvp1 as a regulator of endosomal sorting, melanin transport, and pathogenicity, providing insights into SNX-BAR-mediated pathogenesis in plant pathogenic fungi.