Degradation of α-Subunits, Doa1 and Doa4, are Critical for Growth, Development, Programmed Cell Death Events, Stress Responses, and Pathogenicity in the Watermelon Fusarium Wilt Fungus Fusarium oxysporum f. sp. niveum

The ubiquitin-proteasome system (UPS) regulatesproteinquality or control and plays essential roles in several biologicaland biochemical processes in fungi. Here, we present the characterizationof two UPS components, FonDoa1 and FonDoa4, in watermelon Fusariumwilt fungus, Fusarium oxysporum f.sp. niveum (Fon), and their biologicalfunctions. FonDoa1 localizes in both the nucleus and cytoplasm, whileFonDoa4 is predominantly present in the cytoplasm. Both genes showhigher expression in germinating macroconidia at 12 h. Deletion of FonDoa1 or FonDoa4 affects vegetative growth,conidiation, conidial germination/morphology, apoptosis, and responsesto environmental stressors. FonDoa1, but not FonDoa4, positively regulates autophagy. The targeted disruptionmutants exhibit significantly attenuated pathogenicity on watermelondue to defects in the infection process and invasive fungal growth.Further results indicate that the WD40, PFU, and PUL domains are essentialfor the function of FonDoa1 in Fon pathogenicityand environmental stress responses. These findings demonstrate thepreviously uncharacterized biological functions of FonDoa1 and FonDoa4 in phytopathogenic fungi, providingpotential targets for developing strategies to control watermelonFusarium wilt.