ABSTRACT
This chapter shows that the information available regarding deletion mutants of double-stranded RNA (dsRNA) genetic elements found in plants and fungi. Deletion mutants of Wound Tumor Virus (WTV) were discovered by Black and co-workers during the course of characterizing WTV isolates that had lost the ability to be transmitted by the leafhopper vector. The complete sequence for a wild-type dsRNA segment and its corresponding remnant has been reported in the case of the polyhedrin gene of cytoplasmic polyhedrosis virus, an insect-infecting reovirus. Correlative evidence strongly suggests that dsRNA is the cytoplasmically transmissible determinant responsible for the hypovirulence phenotype. Multiplication of WTV in systemically infected plants and of yeast killer virus and hypovirulence-associated dsRNA in their respective fungal hosts can be considered persistent infections. The chapter focuses on the properties of the remnant molecules, possible mechanisms responsible for their generation, and their potential as experimental tools.
