The SUMOylation Pathway Components Are Required for Vegetative Growth, Asexual Development, Cytotoxic Responses, and Programmed Cell Death Events in f. sp. .

SUMOylation is an essential protein modification process that regulates numerous crucial cellular and biochemical processes in phytopathogenic fungi, and thus plays important roles in multiple biological functions. The present study characterizes the SUMOylation pathway components, including SMT3 (SUMO), AOS1 (an E1 enzyme), UBC9 (an E2 enzyme), and MMS21 (an E3 ligase), in f. sp. (), the causative agent of watermelon Fusarium wilt, in terms of the phylogenetic relationship, gene/protein structures, and basic biological functions. The SUMOylation components FonSMT3, FonAOS1, FonUBC9, and FonMMS21 are predominantly located in the nucleus. , , , and are highly expressed in the germinating macroconidia, but their expression is downregulated gradually in infected watermelon roots with the disease progression. The disruption of and seems to be lethal in . The deletion mutant strains for , , , and are viable, but exhibit significant defects in vegetative growth, asexual reproduction, conidial morphology, spore germination, responses to metal ions and DNA-damaging agents, and apoptosis. The disruption of , , , and enhances sensitivity to cell wall-perturbing agents, but confers tolerance to digestion by cell wall-degrading enzymes. Furthermore, the disruption of , , and negatively regulates autophagy in . Overall, these results demonstrate that the SUMOylation pathway plays vital roles in regulating multiple basic biological processes in , and, thus, can serve as a potential target for developing a disease management approach to control Fusarium wilt in watermelon.