The Cell Wall Integrity MAPK Cascade Regulates Diverse Biological Processes in Parallel With the Pheromone MAPK Pathway in Sclerotinia sclerotiorum and Provides Effective HIGS Targets for Disease Control

Sclerotinia sclerotiorum is one of the most destructive soilborne plant fungal pathogens, devastating many economically important oilseed and vegetable crops. Its overwintering dormant structure sclerotia can survive in soil for years under harsh environments, making disease control particularly challenging. Despite its economic importance, the molecular understanding of sclerotia formation and virulence mechanisms remains fragmented. In this study, throughs both forward genetic screening and reverse genetic analysis, we identified and characterised key components of the cell wall integrity (CWI) MAPK cascade in S. sclerotiorum. Loss-of-function mutants of MAPKKK SsBck1, MAPKK SsMkk1, and MAPK SsSmk3, as well as the scaffold protein SsPro40, exhibited complete loss of sclerotia formation, defect in compound appressorium development, and abolished virulence. Genetic and MAPK phosphorylation analysis further revealed dual requirements of both the CWI cascade and the pheromone MAPK pathway in sclerotia development and virulence. In addition, the conserved CWI downstream transcription factor SsAdv1 was identified as a major regulator of sclerotia formation. Finally, we demonstrated that CWI kinases can serve as effective targets of host-induced gene silencing (HIGS) to suppress Sclerotinia stem rot. Collectively, our findings reveal a regulatory network involving the CWI and pheromone MAPK cascades that coordinates fungal growth, virulence, and sclerotia formation in S. sclerotiorum, providing potential molecular targets for disease control.