O -Mannosyltransferase 1 in Aspergillus fumigatus (AfPmt1p) Is Crucial for Cell Wall Integrity and Conidium Morphology, Especially at an Elevated Temperature

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Abstract
Protein O-mannosyltransferases initiate O mannosylation of secretory proteins, which are of fundamental importance in eukaryotes. In this study, the PMT gene family of the human fungal pathogen Aspergillus fumigatus was identified and characterized. Unlike the case in Saccharomyces cerevisiae, where the PMT family is highly redundant, only one member of each PMT subfamily, namely, Afpmt1, Afpmt2, and Afpmt4, is present in A. fumigatus. Mutants with a deletion of Afpmt1 are viable. In vitro and in vivo activity assays confirmed that the protein encoded by Afpmt1 acts as an O-mannosyltransferase (AfPmt1p). Characterization of the ΔAfpmt1 mutant showed that a lack of AfPmt1p results in sensitivity to elevated temperature and defects in growth and cell wall integrity, thereby affecting cell morphology, conidium formation, and germination. In a mouse model, Afpmt1 was not required for the virulence of A. fumigatus under the experimental conditions used.