The Aspergillus nidulans sfaD gene encodes a G protein beta subunit that is required for normal growth and repression of sporulation

Abstract

flbA encodes an Aspergillus nidulans RGS (regulator of G protein signaling) domain protein that antagonizes FadA (G i α-subunit of heterotrimeric G protein)-mediated growth signaling to allow asexual development. We previously defined and characterized five suppressors of flbA (sfa) loss-of-function mutations and showed that one suppressor (sfaB) resulted from a novel dominant-negative allele of fadA. In this report we show that a second suppressor gene (sfaD) is predicted to encode the β subunit of a heterotrimeric G protein. Deletion of sfaD suppressed all defects resulting from complete loss-of-flbA function mutations, caused a hyperactive sporulation phenotype and severely reduced vegetative growth. However, the sfaD deletion could not suppress the growth activation caused by dominant-activating fadA alleles, indicating that constitutively active FadA can cause proliferative growth in the absence of Gβγ signaling. We propose that SfaD and FadA are both positive growth regulators with partially overlapping functions and that FlbA has an important role in controlling the activities of both proteins. Inactivation of signaling events stimulated by both components of the heterotrimeric G protein is essential for both sexual and asexual sporulation.

Multiple Roles of a Heterotrimeric G-Protein γ-Subunit in Governing Growth and Development of Aspergillus nidulans

“…We found that, while the DsfaD and DgpgADsfaD mutants produced conidiophores within 22 hr of liquid submerged culture, neither the DgpgA mutant nor WT produced conidiophores (Figure 4). Taken together, these results suggest that SfaD (Gb) plays a crucial role in negative regulation of conidiation under submerged culture conditions (Rosén et al 1999;Han et al 2004b) and GpgA may not be involved in this controlling process (see discussion).…”

“…Deletion of gpgA causes severe impairment in fruiting body formation: Our previous study showed that mutational inactivation of SfaD had profound negative effects on sexual fruiting body (cleistothecium) formation (Rosén et al 1999). To examine the possible role of GpgA in sexual development, we determined levels of Hülle cells and cleistothecia production in the DgpgA mutant.…”

“…Radial growth rates were determined every 24 hr for 7 days by measuring colony hyphal extension of individual strains point inoculated on solid medium (both MM and YM). Dry weight of each strain was measured as previously described (Rosén et al 1999). The numbers of conidia and Hü lle cells (per plate) were determined for 5-day cultures of each strain on solid MM or YM.…”

“…One of the suppressors, sfaD, was found to encode a Gb-subunit with the central conserved Trp-Asp sequence that is referred to as the ''WD-40'' motif (Rosén et al 1999). SfaD is required for normal vegetative growth and proper downregulation of conidiation, as well as formation of sexual fruiting bodies (Rosén et al 1999).…”

“…One of the suppressors, sfaD, was found to encode a Gb-subunit with the central conserved Trp-Asp sequence that is referred to as the ''WD-40'' motif (Rosén et al 1999). SfaD is required for normal vegetative growth and proper downregulation of conidiation, as well as formation of sexual fruiting bodies (Rosén et al 1999). The fact that DsfaD suppressed the DflbA-induced fluffy-autolytic phenotype led us to propose that SfaD (with the presumed Gg-subunit) functions in vegetative growth signaling that is negatively regulated by FlbA.…”