The Penicillium digitatum protein O Mannosyltransferase Pmt2 is required for cell wall integrity, conidiogenesis, virulence and sensitivity to the antifungal peptide PAF26

Abstract

The activity of protein O-mannosyltransferases (Pmt) affects the morphogenesis and virulence of fungal pathogens. PMT genes have been recently shown to determine the sensitivity of Saccharomyces cerevisiae to the antifungal peptide PAF26. This study reports the identification and characterisation of the three Pdpmt genes in the citrus postharvest pathogen Penicillium digitatum. The Pdpmt genes are expressed during fungal growth and fruit infection, with the highest induction for Pdpmt2. Pdpmt2 complemented the growth defect of the S. cerevisiae Δpmt2 strain. The Pdpmt2 gene mutation in P. digitatum caused pleiotropic effects, including the reduction of fungal growth and virulence, while its constitutive expression had no phenotypic effect. The Pdpmt2 null mutants also showed a distinctive colourless phenotype with a strong reduction in the number of conidia, which was associated with severe alterations in the development of conidiophores. Additional effects of the Pdpmt2 mutation were hyphal morphological alterations, increased sensitivity to cell wall-interfering compounds, and a blockage of invasive growth. In contrast,the Pdpmt2 mutation increased tolerance to oxidative stress and to the antifungal activity of PAF26. These data confirm the role of protein O-glycosylation in the PAF26-mediated antifungal mechanism present in distant fungal species. Important to future crop protection strategies, this study demonstrates that a mutation rendering fungi more resistant to an antifungal peptide results in severe deleterious effects on fungal growth and virulence.