Recent Advances in Expanding and Understanding Virus-Mediated Attenuation of Fungal Virulence

Abstract

Strains of the chestnut blight fungus Cryphonectria parasitica that contain viral double-stranded (ds) RNA belonging to the genus Hypovirus exhibit reduced levels of virulence (hypovirulence) 1. These elements are transmissible to vegetatively compatible strains of C. parasitica by anastomosis, providing the basis for biological control 2. The potential for effective biological control of chestnut blight has been further advanced by the development of an infectious cDNA copy of a hypovirus dsRNA 3. Strains transformed with these infectious cDNA clones (engineered hypovirulent strains) are able to transmit hypovirus genetic information through mating, a mode of transmission not available to natural hypovirulent strains. This property circumvents barriers to cytoplasmic virus transmission imposed by the fungal vegetative incompatibility system 4,5. Two recent extensions of our studies on virus-mediated attenuation of fungal virulence are reviewed in this chapter. The first involves the development of an infectious hypovirus synthetic transcript and its use to extend fungal host range, thus expanding virus-mediated virulence attenuation to other fungal pathogens. The second concerns additional insights into the molecular mechanisms underlying virus-mediated virulence attenuation.