Mutational activation of a Galphai causes uncontrolled proliferation of aerial hyphae and increased sensitivity to heat and oxidative stress in Neurospora crassa.
Heterotrimeric G proteins, consisting of alpha, beta, and gamma subunits, transduce environmental signals through coupling to plasma membrane-localized receptors. We previously reported that the filamentous fungus Neurospora crassa possesses a Galpha protein, GNA-1, that is a member of the Galphai superfamily. Deletion of gna-1 leads to defects in apical extension, differentiation of asexual spores, sensitivity to hyperosmotic media, and female fertility. In addition, Deltagna-1 strains have lower intracellular cAMP levels under conditions that promote morphological abnormalities. To further define the function of GNA-1 in signal transduction in N. crassa, we examined properties of strains with mutationally activated gna-1 alleles (R178C or Q204L) as the only source of GNA-1 protein. These mutations are predicted to inhibit the GTPase activity of GNA-1 and lead to constitutive signaling. In the sexual cycle, gna-1(R178C) and gna-1(Q204L) strains are female-fertile, but produce fewer and larger perithecia than wild type. During asexual development, gna-1(R178C) and gna-1(Q204L) strains elaborate abundant, long aerial hyphae, produce less conidia, and possess lower levels of carotenoid pigments in comparison to wild-type controls. Furthermore, gna-1(R178C) and gna-1(Q204L) strains are more sensitive to heat shock and exposure to hydrogen peroxide than wild-type strains, while Deltagna-1 mutants are more resistant. In contrast to Deltagna-1 mutants, gna-1(R178C) and gna-1(Q204L) strains have higher steady-state levels of cAMP than wild type. The results suggest that GNA-1 possesses several Gbetagamma-independent functions in N. crassa. We propose that GNA-1 mediates signal transduction pathway(s) that regulate aerial hyphae development and sensitivity to heat and oxidative stresses, possibly through modulation of cAMP levels.
Yang
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Department of Microbiology and Molecular Genetics, University of Texas, Houston Medical School, Houston, Texas 77030, USA.
Borkovich
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D000483:Alleles; D002338:Carotenoids / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000235:genetics* / Q000502:physiology*; D006361:Heating; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009154:Mutation; D009492:Neurospora crassa / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D009995:Osmosis; D018384:Oxidative Stress
D002338:Carotenoids; D006861:Hydrogen Peroxide; D000242:Cyclic AMP; D020558:GTP Phosphohydrolases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go