Family: Botourmiaviridae
Genus: Botoulivirus
Distinguishing features
Botouliviruses have a mono-segmented genome and infect fungi. Some members of the genus have been identified in association with grapevine leaves affected by the oomycete Plasmopara viticola. Botouliviruses are phylogenetically distinct from other botourmiaviruses.
Virion
No true virions are associated with botouliviruses since their genomes have no capsid protein gene.
Genome organization and replication
The Botrytis ourmia-like virus (BOLV) genome is a (+) RNA molecule of 2 903 nucleotides with 45.9% GC content. The complete genome sequence has a 5′ non-coding region (NCR) of 41 nt and a 3′ NCR of 693 nt. The virus genome contains a single open reading frame (ORF) from positions 42 to 2 210, predicted to encode a polypeptide of 722 amino acids (81.88 kDa) that has similarity to the RNA-directed RNA polymerase (RdRP) of the other botouliviruses. The predicted RdRP of BOLV contains the conserved domains of the RdRP of (+) RNA viruses (motifs I-VIII), including the highly conserved core domain GDD (motif VI) (Donaire et al., 2016). Other Botrytis cinerea ourmia-like viruses included in this genus have genomes of 1 937 to 2 213 nt with a single ORF encoding an RdRP of 635 to 735 aa (Ruiz-Padilla et al., 2021). The RdRP of Botrytis cinerea botoulivirus 18 and Botrytis cinerea botoulivirus 19 contains nuclear localisation signals (Wang et al., 2022). The genomes of Sclerotinia sclerotiorum ourmia-like virus 2 and Sclerotinia sclerotiorum ourmia-like virus 3 have been partially sequenced, comprising 2 333 nt and 2 442 nt, respectively (Marzano et al., 2016). Sclerotinia minor botoulivirus 1 has a genome of 2 882 nt with the single ORF encoding an RdRP of 684 aa (Liang et al., 2020). Epicoccum nigrum ourmia-like virus 1 has a genome of 2 749 nt (Nerva et al., 2019b). Plamospara viticola lesion-associated botouliviruses have a genome ranging from 2 352 to 2 556 nt (Chiapello et al., 2020). Pestalotiopsis botourmiavirus 3 has a genome of 2 460 nt (Chen et al., 2021).
Biology
Botrytis ourmia-like virus infects the plant pathogenic fungus Botrytis (Donaire et al., 2016). Other BcOLV have been identified in B. cinerea strains isolated from grapevine (Ruiz-Padilla et al., 2021) or from diseased Paris polyphylla plants (Wang et al., 2022). Sclerotinia sclerotiorum ourmia-like virus 2 and Sclerotinia sclerotiorum ourmia-like virus 3 were identified through metatranscriptomic characterization of the Sclerotinia sclerotiorum virome (Marzano et al., 2016). Sclerotinia minor botoulivirus 1 was identified infecting the phytopathogenic fungus Sclerotinia minor (Liang et al., 2020). Epicoccum nigrum ourmia-like virus 1 was identified in samples of esca symptomatic grapevine plants (Nerva et al., 2019b). Plamospara viticola lesion associated botouliviruses were identified in symptomatic grapevine leaves affected by downy mildew (oomycete Plasmopara viticola) infection (Chiapello et al., 2020). Pestalotiopsis botourmiavirus 3 was found infecting the plant pathogen and endophyte Pestalotiopsis spp. (Chen et al., 2021).
Species demarcation criteria
Amino acid sequence identities of putative RdRP proteins between viruses belonging to different species of the genus Botoulivirus are less than 90%.