TARGETED DISRUPTION OF A FUNGAL G-PROTEIN BETA-SUBUNIT GENE RESULTS IN INCREASED VEGETATIVE GROWTH BUT REDUCED VIRULENCE

Targeted disruption of two G-protein alpha subunit genes in the chestn ut blight fungus Cryphonectria parasitica revealed roles for the G(i a lpha) subunit CPG-1 in fungal reproduction, virulence, and vegetative growth. A second G(alpha) subunit, CPG-2, was found to be dispensable for these functions. We now report the cloning and targeted disruption of a C. parasitica G-protein beta subunit gene. The deduced amino aci d sequence encoded by this gene, designated cpgb-1, was found to share 66.2, 65.9, and 66.7% amino acid identity with G(beta) homologues fro m human, Drosophila, and Dictyostelium origins, respectively, but only 39.7% identity with the Saccharomyces cerevisiae G(beta) homologue ST E4 product. Low stringency Southern hybridization failed to detect any related G(beta) subunit genes in C. parasitica. Targeted disruption o f cpgb-1 resulted in several of the changes previously reported to acc ompany disruption of the C. parasitica G(i alpha) subunit gene cpg-1. These included very significant reductions in pigmentation, asexual sp orulation, and virulence. In contrast to results obtained for G(i alph a) gene disruption, the reduction in virulence resulting from the disr uption of a G(beta) gene was accompanied by increased, rather than dec reased, vegetative growth on synthetic medium. The relevance of these results to mechanisms of fungal virulence is considered.