The C2H2 transcription factor SsZFH1 regulates the size, number and development of apothecia in Sclerotinia sclerotiorum
Sclerotinia sclerotiorum is a notorious phytopathogenic, Ascomycota fungus with a host range of over 600 plant species worldwide. This homothallic, Leotiomycetes species reproduces sexually through a multicellular apothecium which produces and releases ascospores. These ascospores serve as the primary inoculum source for disease initiation in the majority of S. sclerotiorum disease cycles. The regulation of apothecium development for this pathogen and other apothecium-producing fungi remains largely unknown. Here, we report that a C2H2 transcription factor SsZFH1 (zinc finger homologous protein) is necessary for the proper development and maturation of sclerotia and apothecia in S. sclerotiorum and is required for the normal growth rate of hyphae. Furthermore, ΔSszfh1 strains exhibit decreased reactive oxygen species (ROS) accumulation in hyphae, increased melanin deposition and enhanced tolerance to H2O2 in the process of vegetative growth and sclerotia formation. Infection assays on common bean leaves, with thin cuticles, and soybean and tomato leaves, with thick cuticles, suggest that the deletion of Sszfh1 slows the mycelial growth rate, which in turn affect the expansion of leaf lesions. Collectively, our results provide novel insights into the fungal factor mediating maturation of apothecia with additional effects on hyphae and sclerotia development.