Thorough characterization of a new curvulavirid from a Japanese strain of Cryphonectria nitschkei

A new curvulavirid was isolated from a Japanese strain of the filamentous ascomycete Cryphonectria nitschkei and thoroughly characterized. The virus termed Cryphonectria nitschkei curvulavirus 1 (CnCvV1) has a bi-segmented dsRNA genome. CnCvV1 dsRNA1 encodes an RNA-dependent RNA polymerase (592 amino acids), while dsRNA2 possesses two ORFs, one that encodes a protein associated with the genomic dsRNA and the other that encodes a hypothetical protein of unknown function. CnCvV1 could be experimentally introduced into another virus-free strain of C. nitschkei and two strains of different fungal species within the genus Cryphonectria ( Cryphonectria parasitica and Cryphonectria carpinicola ). Based on phenotypic comparison, the virus caused asymptomatic infection in the three newly established fungal strains. However, there was a reduced colony growth rate and increased CnCvV1 accumulation in an RNA silencing-deficient mutant (Δ dcl2 ), relative to the wt strain EP155 of a model virus host fungus ( C. parasitica ). These findings suggest that CnCvV1 is targeted by RNA silencing in C. parasitica . This study provides a foundation for further exploration of curvulavirids that have been biologically understudied.