Family: Botourmiaviridae

Genus: Betarhizoulivirus

Distinguishing features

Betarhizouliviruses have a mono-segmented genome, infect fungi, and are phylogenetically distinct from other botourmiaviruses.

Virion

No true virions are associated with betarhizouliviruses since their genomes have no capsid protein gene.

Genome organization and replication

The Rhizoctonia solani ourmia-like virus 5 (RsOLV5) genome is a (+) RNA molecule of 5 234 nucleotides with 55% GC content. The complete genome sequence has a 5′ non-coding region (NCR) of 919 nt and a 3′ NCR of 202 nt. The virus genome contains a single open reading frame from positions 920 to 5 032, predicted to encode a polypeptide of 1 370 amino acids (153.22 kDa) that has similarity to the RNA-directed RNA polymerase (RdRP) of the rhizouliviruses (Picarelli et al., 2019). The genome of Armillaria mellea ourmia-like virus 1 (AmOlV1) is 3 919 nt in length and contains a single ORF from positions 923 to 3 649, predicted to code for a protein of 908 amino acids (Linnakoski et al., 2021). This virus was mistakenly assigned to the species Betarhizoulivirus alphamellea in the genus Betarhizoulivirus - a future Taxonomic Proposal will move this species to the genus Rhizoulivirus.

Biology

RsOLV5 infects the plant pathogenic fungus Rhizoctonia solani (Picarelli et al., 2019). Armillaria mellea ourmia-like virus 1, incorrectly assigned to a species in this genus, infects the edible fungus Armillaria mellea (Linnakoski et al., 2021).

Species demarcation criteria

There are two species in the genus. However, the species Betarhizoulivirus alphamellea has been incorrectly assigned. A future Taxonomic Proposal will move the species to the genus Rhizoulivirus. Members of distinct species in the genus are expected to have amino acid sequence identities of their putative RdRP proteins of less than 90%.