Mycoviruses (Fungal viruses) are widespread throughout the major taxonomic groups of fungi, including yeasts, mushrooms, and pathogenic fungi that infect plants, insects, and humans. The first mycovirus, named La France isometric virus (LIV), was reported in Agaricus bisporus as “La France disease” in 1962 [6]. Since then, numerous mycoviruses have been discovered in all major fungal groups. Most mycoviruses have RNA genomes and are divided into eleven families with positive single-stranded (+ ss) RNA genomes, three families with negative single-strand (-ss) RNA genomes, nine families with double-stranded (ds) RNA genomes, one family with ssDNA genomes, and two families with RT-ssRNA genomes [9, 10, 16]. Mycoviruses with + ssRNA genomes are now classified into eleven families: Alphaflexiviridae, Barnaviridae, Botourmiaviridae, Deltaflexiviridae, Endornaviridae, Gammaflexiviridae, Hadakaviridae, Hypoviridae, Mitoviridae, Narnaviridae, and Yadokariviridae [9, 16].
The order Tymovirales consists of five approved families (Alphaflexiviridae, Betaflexiviridae, Deltaflexiviridae, Gammaflexiviridae, and Tymoviridae) [2]. To date, twelve mycoviruses belong to the order Tymovirales. These mycoviruses include Botrytis virus X (BVX, family Alphaflexiviridae), Botryosphaeria dothidea botrexvirus 1 (BdBV1, family Alphaflexiviridae), Sclerotinia sclerotiorum debilitation-associated RNA virus (SSDaV, family Alphaflexiviridae), Botrytis virus F (BVF, family Gammaflexiviridae), Alternaria tenuissima deltaflexivirus 1 (AtDFV1, Deltaflexiviridae), Fusarium graminearum deltaflexivirus 1 (FgDFV1, Deltaflexiviridae), Sclerotinia sclerotiorum deltaflexivirus 1 (SsDFV1, Deltaflexiviridae), Sclerotinia sclerotiorum deltaflexivirus 2 (SsDFV2, Deltaflexiviridae), Sclerotinia sclerotiorum deltaflexivirus 3 (SsDFV3, Deltaflexiviridae), Fusarium graminearum mycotymovirus 1 (FgMTV1, Tymoviridae), Sclerotinia sclerotiorum mycotymovirus 1 (SsMTV1, Tymoviridae), and Rhizoctonia solani flexivirus 1 (RsFV-1, unclassified flexivirus) [1, 3, 4, 7, 8, 12, 13, 15, 22–25]. The family Deltaflexiviridae includes one genus, Deltaflexivirus. Except for SsDFV3 with a segmented genome [15], the other four deltaflexiviruses have unsegmented genomes [3, 4, 12, 23]. The gene encoding an RNA replicase is the only one conserved among all deltaflexiviruses.
Pleurotus ostreatus is a widely cultivated edible fungus worldwide. It has high nutritional and medicinal values, such as enhancing immunity, enhancing memory, lowering blood sugar, and lowering blood lipids [21]. Five mycoviruses have been reported in Pleurotus ostreatus, including four dsRNA viruses belonging to the family Partitiviridae: Oyster mushroom isometric virus (OMIV), Pleurotus ostreatus virus 1 (PoV1), Pleurotus ostreatus spherical virus (POSV), PoV-ASI2792, and the only ssRNA virus: Oyster mushroom spherical virus (OMSV, an unassigned genus of the Tymoviridae family) [14, 17–19, 26].
Here, we report a novel mycovirus isolated from Pleurotus ostreatus strain ZP6. Genetic organization and phylogenetic analysis suggested that the virus is a member of the genus Deltaflexivirus of the family Deltaflexiviridae. Therefore, we have tentatively named this virus Pleurotus ostreatus deltaflexivirus 1 (PoDFV1).