Gβγ-mediated growth and developmental control in Aspergillus fumigatus

The roles of the G beta gamma subunits of the opportunistic human pathogen Aspergillus fumigatus were investigated. The predicted AfuSfaD (G beta) protein consists of 353 amino acids and shows 94-98% similarity with other Aspergillus G beta subunits. AfuGpgA consists of 90 amino acids showing 95-98% identity with other fungal G-protein gamma subunits. The deletion (Delta) of AfusfaD or AfugpgA resulted in severe impairment in vegetative growth, conidial germination and conidial trehalose breakdown. While the total number of conidia produced by Delta AfusfaD and Delta AfugpgA strains on solid medium was only about 1% of wild type, the growth-adjusted conidiation levels were twofold higher than those of wild type. Enhanced formation of conidiophores and elevated AfubrlA mRNA levels were observable in Delta AfusfaD or Delta AfugpgA strains in liquid submerged culture. Moreover, overexpression of AfusfaD or AfugpgA caused reduced levels of submerged culture conidiation, indicating that G beta gamma is involved in negative regulation of conidiation. Gliotoxin and other metabolites were not detected in the chloroform extracts of Delta AfusfaD and Delta AfugpgA culture filtrates. Northern blot analyses revealed that, while AfulaeA mRNA levels unchanged, accumulation of gliZ mRNA was delayed by Delta AfusfaD or Delta AfugpgA. A model summarizing the roles of AfusfaD and AfugpgA in A. fumigatus is presented.