Genetical and O-glycoproteomic analyses reveal the roles of three protein O-mannosyltransferases in phytopathogen Fusarium oxysporum f.sp. cucumerinum

Protein O-mannosyltransferases (PMTs) have been identified in fungi but not in plants and nematodes, which makes PMTs become attractive targets for developing a new strategy against phytopathogens. Three PMTs have been identified in Fusarium oxysporum, a fungal pathogen that causes vascular wilt in a broad range of economical crops. By deletion or suppression of the pmt genes, we showed that all mutants displayed retarded growth, reduced conidiation, cell wall defects, ER stress and attenuated virulence in F. oxysporum f.sp. cucumerinum. In addition, the Delta prnt1 exhibited reduced thermotolerance, while the Delta pmt4 and the pmt2 conditional mutant exhibited abnormal polarized growth. Comparative glycoproteome analysis of these pmt mutants revealed that PMTs preferentially modified random coils with flanking regions rich in Ser, Thr, Ala, Glu, Asp and Lys at the stem region of membrane proteins, the N-terminal region close to signal peptide of secreted proteins, or surface of soluble proteins. PMT1 specifically acted on nuclear proteins and proteins that are responsible for protein folding, which might contribute to thermotolerance. PMT4 specifically acted on the membrane and soluble proteins in secretory pathways, especially the GPI anchoring pathway, which might contribute to synthesis and transportation of GPI anchored proteins and thus polarized growth. PMT2 was responsible for modification of proteins that are required for protein folding and cell wall synthesis, which might make PMT2 essential. Our results gave an insight to understanding of the roles of each O-mannosyltransferase in F. oxysporum f.sp. cucumerinum and provide a new perspective to prevent Fusarium wilt.