Constitutively activated Galpha negatively regulates virulence, reproduction and hydrophobin gene expression in the chestnut blight fungus Cryphonectria parasitica.

Disruption of the gene encoding Galpha subunit cpg-1 in the chestnut blight fungus Cryphonectria parasitica reduces growth and pigmentation and abolishes reproduction and virulence. We now report the consequences of mutations designed to constitutively activate (Q204-L and R178-C) CPG-1-mediated signaling. Introduction of cpg-1-QL or cpg-1-RC into wild type, Deltacpg-1 and Deltacpgb-1 (Gbeta) mutant strains resulted in a dominant phenotype characterized by a complete absence of aerial hyphae, pigmentation, conidia production and virulence. Opposing responses of Deltacpg-1 and activated mutant strains to chronic heat, hyperosmolarity and oxidative stress suggested that CPG-1 plays a role in mediating stress response. Growth of the cpg-1 mutant strains proceeded at wild-type level in rich liquid medium, but was severely curtailed on solid medium and absent in chestnut tissue, indicating the importance of CPG-1 mediated signaling under these harsher conditions. Both cpg-1 deletion and activating CPG-1 mutations resulted in post-transcriptional alterations in the accumulation of CPG-1 and/or CPGB-1, providing evidence for extensive post-transcriptional regulation of G-protein subunit accumulation in C. parasitica. Finally, the absence of aerial hyphae and the easily wettable phenotype exhibited by the QL and RC mutants correlated with reduced expression of the gene encoding cryparin, suggesting G-protein-mediated regulation of a fungal hydrophobin.