Heterotrimeric G-proteins of a filamentous fungus regulate cell wall composition and susceptibility to a plant PR-5 protein

Membrane permeabilizing plant defensive proteins first encounter the fungal cell wall that can harbor specific components that facilitate or prevent a ccess to the plasma membrane. However, signal transduction pathways control ling cell wall composition in filamentous fungi are largely unknown. We rep ort here that the deposition of cell wall constituents that block the actio n of osmotin (PR-5), an antifungal plant defense protein, against Aspergill us nidulans requires the activity of a heterotrimeric G-protein mediated si gnaling pathway. The guanidine nucleotide GDP beta S, that locks G-proteins in a GDP bound inactive form, inhibits osmotin-induced conidial lysis. A d ominant interfering mutation in FadA, the alpha-subunit of a heterotrimeric G-protein, confers resistance to osmotin, A deletion mutation in SfaD, the beta-subunit of a heterotrimeric G-protein also increases osmotin resistan ce. Aspergillus nidulans strains bearing these mutations also have increase d tolerance to SDS, reduced cell wall porosity and increased chitin content in the cell wall.