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

November 1997 , Volume 10 , Number  8
Pages  984 - 993

Shin Kasahara and Donald L. Nuss

Center for Agricultural Biotechnology, University of Maryland Biotechnology Institute, University of Maryland, College Park 20742-4450, U.S.A.

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Accepted 18 July 1997.

Targeted disruption of two G-protein α subunit genes in the chestnut blight fungus Cryphonectria parasitica revealed roles for the G 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 G subunit gene cpg-1. These included very significant reductions in pigmentation, asexual sporulation, and virulence. In contrast to results obtained for G 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.

Additional keywords: hypovirulence, signal transduction.

© 1997 The American Phytopathological Society