Overlapping Functions for Two G Protein α Subunits in Neurospora crassa

Abstract

Heterotrimeric G proteins, consisting of α, β and γ subunits, mediate a variety of signaling pathways in eukaryotes. We have previously identified two genes, gna-1 and gna-2, that encode G protein α subunits in the filamentous fungus Neurospora crassa. Mutation of gna-1 results in female infertility and sensitivity to hyperosmotic media. In this study, we investigate the expression and functions of gna-2. Results from Western analysis and measurements of gna-2 promoter-lacZ fusion activity indicate that gna-2 is expressed during the vegetative and sexual cycle of N. crassa in both A and a mating types. Activating mutations predicted to abolish the GTPase activity of GNA-2 cause subtle defects in aerial hyphae formation and conidial germination. Extensive phenotypic analysis of Δgna-2 strains did not reveal abnormalities during vegetative or sexual development. In contrast, deletion of gna-2 in a Δgna-1 strain accentuates the Δgna-1 phenotypes. Δgna-1 Δgna-2 strains have a slower rate of hyphal apical extension than Δgna-1 strains on hyperosmotic media. Moreover, Δgna-1 Δgna-2 mutants have more pronounced defects in female fertility than Δgna-1 strains. We propose that gna-1 and gna-2 have overlapping functions and may constitute a gene family. This is the first report of G protein α subunits with overlapping functions in eukaryotic microbes.

Regulator of G Protein Signaling Proteins Control Growth, Development and Cellulase Production in Neurospora crassa

“…We analyzed the strains for three major events during sexual development: the production of protoperithecia, perithecia and ascospores. The findings confirmed published results for the three Gα mutants [ 11 , 12 , 13 , 19 , 20 ], with Δ gna-2 being like wild type, Δ gna-1 producing abnormal perithecia and no ascospores, and Δ gna-3 forming fewer protoperithecia and perithecia than wild type ( Table 2 ). Consistent with previous findings, strains carrying the gna-1 Q204L allele produced fewer perithecia and ascospores than wild type [ 11 , 19 ], while gna-2 Q205L strains were normal [ 12 ].…”

“…The findings confirmed published results for the three Gα mutants [ 11 , 12 , 13 , 19 , 20 ], with Δ gna-2 being like wild type, Δ gna-1 producing abnormal perithecia and no ascospores, and Δ gna-3 forming fewer protoperithecia and perithecia than wild type ( Table 2 ). Consistent with previous findings, strains carrying the gna-1 Q204L allele produced fewer perithecia and ascospores than wild type [ 11 , 19 ], while gna-2 Q205L strains were normal [ 12 ]. In this study, we also observed that gna-3 Q208L strains did not produce protoperithecia, perithecia or ascospores ( Table 2 ).…”

“…Previous research has shown that the three Gα protein subunits have important functions during growth and development in N. crassa , with GNA-2 often serving a compensatory role to GNA-1 and GNA-3 [ 11 , 12 , 13 , 19 , 20 ]. In this study, we investigated roles for the seven RGS genes during the N. crassa life cycle.…”

“…Previous studies have demonstrated that perturbation of components in the G protein signaling pathway results in altered growth and development in N. crassa [ 9 ]. N. crassa possesses three Gα proteins GNA-1, GNA-2, and GNA-3 ( G uanine N ucleotide-binding protein A lpha—1/2/3) [ 10 , 11 , 12 , 13 ], two predicted Gβ proteins GNB-1 ( G uanine N ucleotide-binding protein B eta -1) and CPC-2 ( C ross P athway C ontrol -2) [ 14 , 15 , 16 ] and one Gγ protein GNG-1 ( G uanine N ucleotide-binding protein G amma -1) [ 17 ]. Various G protein subunits have been shown to regulate hyphal growth rate, aerial hyphae height, macroconidia abundance, development of protoperithecia and perithecia, and stress resistance.…”

Correction: The Guanine Nucleotide Exchange Factor RIC8 Regulates Conidial Germination through Gα Proteins in Neurospora crassa

“…In contrast, the N. crassa Dgna-2 mutant displays only a mild phenotype during growth on poor carbon sources [4]. However, loss of GNA-2 exacerbates phenotypes of the Dgna-1 and Dgna-3 mutants, indicating that GNA-2 shares overlapping functions with the other two Ga subunits [5,6]. Indeed, all three G proteins are thought to act together to regulate certain processes, as mutants lacking GNA-1 and GNA-3 or all three Ga subunits are severely impaired in growth on solid medium, inappropriately conidiate in submerged liquid culture and do not produce female reproductive structures [6].…”