Family: Botourmiaviridae
Genus: Scleroulivirus
Distinguishing features
Sclerouliviruses have a mono-segmented genome, infect fungi, and are phylogenetically distinct from other botourmiaviruses. The genome of Magnaporthe oryzae botourmiavirus 9 is polyadenilated at the 3′-end (Zhou et al., 2021).
Virion
No true virions are associated with sclerouliviruses since their genomes have no capsid protein gene.
Genome organization and replication
The genome of Sclerotinia sclerotiorum ourmia-like virus 1 (SsOLV1) is a positive-sense RNA molecule of 3 180 nt. The SsOLV1 genome has a single open reading frame (ORF) from nt positions 281 to 2 341, predicted to encode a polypeptide of 686 aa. This protein is most closely related to the RNA-directed RNA polymerase (RdRP) of soybean leaf-associated ourmiavirus 1 (49 % amino acid sequence identity), although it is closely related to other ourmia-like mycoviruses and plant ourmiaviruses. The genomes of soybean leaf-associated ourmiavirus 1 and soybean leaf-associated ourmiavirus 2 have been partially sequenced (Marzano and Domier 2016). Pyricularia oryzae ourmia-like virus 2 and Pyricularia oryzae ourmia-like virus 3 have genomes of 1 671 and 2 557 nt, respectively (Ohkita et al., 2019). The genome of Cladosporium uredinicola ourmia-like virus 1 is 2 593 nt (Nerva et al., 2019b). Oidiodendron maius ourmia-like virus 1 has a genome of 2 087 nt (Sutela et al., 2020). Eighteen Plasmopara viticola lesion-associated ourmia-like sclerouliviruses with varying genome lengths are also included in this genus (Chiapello et al., 2020). Magnaporthe oryzae botourmiavirus 9 has a full-length nucleotide sequence of 2 812 nt long (Zhou et al., 2021). Pestalotiopsis botourmiavirus 2 has a genome of 2 634 nt (Chen et al., 2021).
Biology
Sclerotinia sclerotiorum ourmia-like virus 1 infects the plant pathogenic fungus Sclerotinia sclerotiorum (Marzano et al., 2016). Soybean leaf-associated ourmiavirus 1 and soybean leaf-associated ourmiavirus 2 have been isolated from soybean leaves (Marzano and Domier 2016). Pyricularia oryzae ourmia-like virus 2 and Pyricularia oryzae ourmia-like virus 3 have been detected in wheat lesions produced by Pyricularia oryzae (Ohkita et al., 2019). Cladosporium uredinicola ourmia-like virus 1 has been isolated from grapevine wood tissues (Nerva et al., 2019b). Oidiodendron maius ourmia-like virus 1 infects the fungus Oidiodendron maius (Sutela et al., 2020). Plasmopara viticola lesion-associated ourmia-like sclerouliviruses were identified in grapevine leaves affected by downy mildew (oomycete Plasmopara viticola) infection (Chiapello et al., 2020). Magnaporthe oryzae botourmiavirus 9 was found infecting the rice blast fungus Magnaporthe oryzae (Zhou et al., 2021). Pestalotiopsis botourmiavirus 2 was found infecting the plant pathogen and endophyte fungi Pestalotiopsis spp. (Chen et al., 2021).
Species demarcation criteria
Amino acid sequence identities of putative RdRP proteins between viruses belonging to different species in the genus Scleroulivirus are less than 90%.