Engineering hypoviruses for fundamental and practical applications

The concept of using a parasite of a parasite for disease control is appealing from both an intellectual and an ecological perspective. The phenomenon of transmissible hypovirulence, in which virulence of the chestnut blight fungus, Cryphonectria parasitica, is attenuated by double-stranded RNA viruses in the family Hypoviridae, is often cited as a classic example of this approach to biological disease control. Progress in the development of an infectious cDNA-based reverse genetics system for hypoviruses has provided the means for engineering these viral agents for both fundamental and practical applications, e.g., as a tool for probing signal transduction processes underlying fungal pathogenesis and for enhanced biocontrol potential. This chapter describes the basic techniques used for manipulating hypovirus genomes and provides specific examples of how they are being applied to identify virus-encoded determinants responsible for altering fungal host phenotype, to gain insights into dispensable and essential elements of viral replication, and to fine tune the interaction between a fungal pathogen and its plant host.