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

Disruption of the gene encoding Got 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 wildtype 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. (C) 2003 Elsevier Science (USA). All rights reserved.