Aspergillus fumigatus G-protein coupled receptors GprM and GprJ are important for the regulation of the cell wall integrity pathway, secondary metabolite production, and virulence

G-protein
coupled receptors (GPCRs) are extracellular signalling receptors that sense
environmental cues to coordinate a biological response. Fungi sense their
environment primarily through GPCR-mediated signalling pathways, which in turn
regulate fungal development, metabolism, virulence and mycotoxin biosynthesis. A. fumigatus is an important human
pathogen that causes aspergillosis, a heterogeneous group of diseases that
presents a wide range of clinical manifestations. Here, we investigate in detail the role of the GPCRs
GprM and GprJ in growth and gene expression. GprM and GprJ are important for melanin
production and the regulation of the cell wall integrity (CWI) pathway. Overexpression of gprM and gprJ causes a 20 and 50% reduction in growth rate when compared to
the wild-type (WT) strain, and increases sensitivity to cell wall-damaging
agents. Phosphorylation of the CWI protein kinase MpkA is increased in the ΔgprM and ΔgprJ strains and decreased in the overexpression mutants when compared
to the WT strain. Furthermore, differences in cell wall polysaccharide
concentrations and organization were observed in these strains. RNA-sequencing suggests that GprM and GprJ negatively
regulate genes encoding secondary metabolites (SMs). Mass spectrometry analysis confirmed that the
production of fumagillin,
pyripyropene, fumigaclavine C, fumiquinazoline, and fumitremorgin is reduced in
the ΔgprM and ΔgprJ strains, and that this regulation occurs, at least partially,
through the activation of MpkA. Overexpression of grpM also resulted in the regulation of many transcription factors,
with AsgA predicted to function downstream of GprM and MpkA signalling.
Finally, we show that the
ΔgprM and ΔgprJ mutants are reduced in virulence in the Galleria mellonella insect model of
invasive aspergillosis. This work further
contributes to unravelling functions of A.
fumigatus GPCRs and shows that GprM and GprJ are essential for CWI,
secondary metabolite production and virulence.