Virus-mediated or transgenic suppression of a G-protein alpha subunit and attenuation of fungal virulence.

Strains of the chestnut blight fungus Cryphonectria parasitica harboring RNA viruses of the genus Hypovirus exhibit significantly reduced levels of virulence (called hypovirulence). The accumulation of a heterotrimeric GTP-binding protein (G protein) alpha subunit of the Gi class was found to be reduced in hypovirus-containing C. parasitica strains. Transgenic cosuppression, a phenomenon frequently observed in transgenic plants, reduced the accumulation of this alpha subunit in virus-free fungal strains. Significantly, the resulting transgenic fungal strains were also hypovirulent. These results indicate a crucial role for G-protein-linked signal transduction in fungal pathogenesis and suggest a molecular basis for virus-mediated attenuation of fungal virulence.