from James D. Kim, Patrick Schacht, Amruta Garud, Gyungsoon Park and Katherine A. Borkovich writing in Neurospora: Genomics and Molecular Biology:
One of the major systems used by Neurospora crassa to sense and respond to changes in the environment is the heterotrimeric G protein signaling pathway. This system translates signals detected by G protein coupled receptors (GPCRs) or the cytosolic protein RIC8 to an associated intracellular heterotrimeric G protein (α, β and Gγ subunit) to regulate GDP/GTP exchange on the Gα protein. Gα-GTP and the Gβ γdimer have the potential to regulate downstream effectors. In N. crassa, all five characterized G protein subunits have some function in sexual and asexual growth and development, nutrient sensing or stress responses. Biochemical evidence indicates that the Gβ and Gγ subunits form a heterodimer, and that loss of either subunit leads to degradation of Gα proteins. GPCRs have been implicated in the pheromone response (PRE-1 and PRE-2), perithecial development (GPR-1) and carbon sensing (GPR-4). GTP binding assays using purified proteins demonstrate that RIC8 activates GDP/GTP exchange on two Gα proteins. cAMP is an important second messenger that regulates aspects of asexual and sexual development. Furthermore, metabolomics experiments using 1H-NMR support a role for one G Gα protein in nutrient sensing.
Further reading: Neurospora: Genomics and Molecular Biology