Severe impairment of growth and differentiation in a Neurospora crassa mutant lacking all heterotrimeric G alpha proteins.

Heterotrimeric G alpha proteins play a critical role in regulating growth and differentiation in filamentous fungi. No systematic analysis of functional relationships between subunits has been investigated. This study explores the relative contributions of Neurospora crassa G alpha subunits, gna-1, gna-2, and gna-3, in directing development by analyzing strains deleted for various combinations of these genes. Although viable, mutants lacking all G alpha subunits or gna-1 and gna-3 are severely restricted in apical growth, forming small colonies. These strains form little aerial hyphae during asexual development on solid medium and exhibit inappropriate sporulation in submerged cultures. Similar to all strains carrying the Delta gna-1 mutation, these mutants are female sterile. Defects attributed to gna-2 are observed only in conjunction with the loss of gna-1 or gna-3, suggesting a minor role for this G alpha in N. crassa biology. Results from analysis of adenylyl cyclase and epistatic studies with the cAMP-dependent protein kinase regulatory subunit (mcb) indicate separate functions for GNA-1 and GNA-3 in cAMP metabolism and additional cAMP-independent roles for GNA-1. These studies indicate that although G alpha subunits are not essential for viability in filamentous fungi, their loss results in an organism that cannot effectively forage for nutrients or undergo asexual or sexual reproduction.