cDNA-derived hypovirus RNA in transformed chestnut blight fungus is spliced and trimmed of vector nucleotides.

Unencapsidated double-stranded viral RNAs belonging to the genus Hypovirus attenuate virulence of the chestnut blight fungus, Cryphonectria parasitica. A full-length cDNA clone of hypovirus CHV1-713 double-stranded RNA was recently shown to be infectious when introduced into the C. parasitica genome by DNA-mediated transformation. In this study, we show that the viral RNA derived from the chromosomally integrated cDNA copy is trimmed of extraneous vector nucleotide sequences. The cDNA-derived viral RNA was also found to contain a 73-bp deletion located within the 5'-noncoding leader sequence as a result of a pre-mRNA splicing event. Implications of these results are discussed in terms of hypovirus RNA replication and anticipated field studies involving engineered hypovirulent C. parasitica strains.