Characterization of a novel alternavirus infecting the fungal pathogen Fusarium solani

A novel dsRNA mycovirus was found in Fusarium solani (F. solani) strain NW-FVA 2572. The fungus was originally isolated from a root, associated with stem collar necrosis of Fraxinus excelsior L. The viral genome is composed of four segments, which range from around 3.5 kbp to 1.7 kbp (RNA 1: 3522 bp; RNA 2: 2633 bp; RNA 3: 2403 bp; RNA 4: 1721 bp). The segments share a conserved and capped 5'-terminus and their 3'-termini are polyadenylated. Protein sequencing showed that the viral RdRP is encoded on segment 1. The virus clusters together with Aspergillus mycovirus 341 (AsV341), Aspergillus heteromorphus alternavirus 1 (AheAV1), Aspergillus foetidus virus-fast (AfV-F) and Cordyceps chanhua alternavirus 1 (CcAV1). As highest value, the RdRP showed 61.50% identical amino acids with P1 of the AfV-F. The capsid protein is encoded on segment 3, the proteins encoded on RNA 2 and RNA 4 are of unknown function. Segment 4 harbors large UTRs (186 nts at the 5'-terminus and 311 nts at the 3'-terminus). Based on its genome organization and phylogenetic position, the virus is suggested to be a new member of the proposed family Alternaviridae and was therefore named Fusarium solani alternavirus 1 (FsAV1). This is the first report of an Alternavirus infecting a fungus of the F. solani species complex (FSSC).