Sumoylation-dependent control of Pmk1 phosphorylation during Magnaporthe oryzae infection

Rice blast disease, caused by Magnaporthe oryzae, significantly threatens global rice yields. The Pmk1-MAPK signaling pathway is crucial for the infection process, but the precise regulatory mechanisms of Pmk1 remain unclear. Our research reveals that sumoylation of Pmk1 is vital for its infectious function. A sumoylation site at K347 and two small ubiquitin-related modifier (SUMO)-interacting motifs (SIMs) in Pmk1 are highly conserved across fungi. This sumoylation, orchestrated by Smt3 and Siz1, reduces the phosphorylation of Pmk1 by tuning its interaction with Mst7. The Pmk1 sumoylation is high in hyphae and less in conidia, and it intensifies during appressorium maturation. It may act as a molecular brake to prevent excessive Pmk1 phosphorylation during appressorium formation, without affecting phosphatase Pmp1 or the localization of Pmk1. Mutations at K347 lead to hyperphosphorylation of Pmk1 and Mst12, and overexpression of appressorium-related genes. The Δpmk1/Pmk1^K347R mutant shows deficiencies in storage utilization, turgor accumulation, and septin ring formation. Our study highlights the critical role of sumoylation dynamically balancing Pmk1 function via phosphorylation crosstalk, crucial for infection of M. oryzae, thus proposing a conserved target for antifungal strategies across fungal pathogens.