Characterization of a Fungal Virus Representing a Novel Genus in the Family Alphaflexiviridae

Sclerotinia sclerotiorum is an ascomycetous fungus and hosts various mycoviruses. In this study, a novel fungal alphaflexivirus with a special genomic structure, named Sclerotinia sclerotiorum alphaflexivirus 1 (SsAFV1), was cloned from a hypovirulent strain, AHS31. Strain AHS31 was also co-infected with two botourmiaviruses and two mitoviruses. The complete genome of SsAFV1 comprised 6939 bases with four open reading frames (ORFs), a conserved 5 '-untranslated region (UTR), and a poly(A) tail in the 3 ' terminal; the ORF1 and ORF3 encoded a replicase and a coat protein (CP), respectively, while the function of the proteins encoded by ORF2 and ORF4 was unknown. The virion of SsAFV1 was flexuous filamentous 480-510 nm in length and 9-10 nm in diameter. The results of the alignment and the phylogenetic analysis showed that SsAFV1 is related to allexivirus and botrexvirus, such as Garlic virus X of the genus Allexivirus and Botrytis virus X of the genus Botrevirus, both with 44% amino-acid (aa) identity of replicase. Thus, SsAFV1 is a novel virus and a new genus, Sclerotexvirus, is proposed to accommodate this novel alphaflexivirus.