Regulators of G-protein signalling in Aspergillus nidulans: RgsA downregulates stress response and stimulates asexual sporulation through attenuation of GanB (Galpha) signalling.

Regulators of G-protein signalling play a crucial role in controlling the degree of heterotrimeric G-protein signalling. In addition to the previously studied flbA, we have identified three genes (rgsA, rgsB and rgsC) encoding putative RGS proteins in the genome of Aspergillus nidulans. Characterization of the rgsA gene revealed that RgsA downregulates pigment production and conidial germination, but stimulates asexual sporulation (conidiation). Deletion of rgsA (DeltargsA) resulted in reduced colony size with increased aerial hyphae, elevated accumulation of brown pigments as well as enhanced tolerance of conidia and vegetative hyphae against oxidative and thermal stress. Moreover, DeltargsA resulted in conidial germination in the absence of a carbon source. Deletion of both flbA and rgsA resulted in an additive phenotype, suggesting that the G-protein pathways controlled by FlbA and RgsA are different. Morphological and metabolic alterations caused by DeltargsA were suppressed by deletion of ganB encoding a Galpha subunit, indicating that the primary role of RgsA is to control negatively GanB-mediated signalling. Overexpression of rgsA caused inappropriate conidiation in liquid submerged culture, supporting the idea that GanB signalling represses conidiation. Our findings define a second and specific RGS-Galpha pair in A. nidulans, which may govern upstream regulation of fungal cellular responses to environmental changes.