Targeted Disruption of a Fungal G-Protein β Subunit Gene Results in Increased Vegetative Growth but Reduced Virulence

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Abstract
Targeted disruption of two G-protein α subunit genes in the chestnut blight fungus Cryphonectria parasitica revealed roles for the Giα subunit CPG-1 in fungal reproduction, virulence, and vegetative growth. A second Gα 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 β subunit gene. The deduced amino acid sequence encoded by this gene, designated cpgb-1, was found to share 66.2, 65.9, and 66.7% amino acid identity with Gβ homologues from human, Drosophila, and Dictyostelium origins, respectively, but only 39.7% identity with the Saccharomyces cerevisiae Gβ homologue STE4 product. Low stringency Southern hybridization failed to detect any related Gβ subunit genes in C. parasitica. Targeted disruption of cpgb-1 resulted in several of the changes previously reported to accompany disruption of the C. parasitica Giα subunit gene cpg-1. These included very significant reductions in pigmentation, asexual sporulation, and virulence. In contrast to results obtained for Giα gene disruption, the reduction in virulence resulting from the disruption of a Gβ gene was accompanied by increased, rather than decreased, vegetative growth on synthetic medium. The relevance of these results to mechanisms of fungal virulence is considered.