A novel putative virus of Gremmeniella abietina type B (Ascomycota: Helotiaceae) has a composite genome with endornavirus affinities

Abstract

Ascospore and mycelial isolates of Gremmeniella abietina type B were found to contain three different dsRNA molecules with approximate lengths of 11, 5 and 3 kb. The 11 kb dsRNA encoded the genome of a putative virus and is named Gremmeniella abietina type B RNA virus XL (GaBRV-XL). GaBRV-XL probably exists in an unencapsulated state. We identified two distinct dsRNAs (10 374 and 10 375 bp) of GaBRV-XL, both of which coded for the same putative polyprotein (3249 amino acids) and contained four regions similar to putative viral methyltransferases, DExH box helicases, viral RNA helicase 1 and RNA-dependent RNA polymerases. While a cysteine-rich region with several CxCC motifs in GaBRV-XL was similar to that of putative endornaviruses, cluster analyses of conserved regions revealed GaBRV-XL to be distinct from a broad range of viral taxa but most closely related to Discula destructiva virus 3. Collectively, these findings suggest that GaBRV-XL represents a novel virus group related to endornaviruses.