Search Results (5)

Pleurotus ostreatus, a globally cultivated oyster mushroom, is susceptible to viral infections that threaten yield and quality. This study reports the identification and characterization of three novel viruses from a symptomatic P. ostreatus strain K3: Pleurotus ostreatus deltaflexivirus 2, 3, and 4 (PoDFV2, PoDFV3, PoDFV4). Complete genome sequencing revealed that they are single-stranded, positive-sense RNA viruses with lengths of 7809 nt, 7771 nt, and 7786 nt, encoding 5, 2, and 4 open reading frames (ORFs), respectively. The largest open reading frame (ORF1) encodes a putative replication-associated polyprotein (RP) containing three conserved domains—viral RNA methyltransferase (Mtr), viral RNA helicase (Hel), and RNA-dependent RNA polymerase (RdRp). Based on genomic sequence analysis, multiple sequence alignments, and phylogenetic analysis, PoDFV2–4 were identified as novel viruses of the genus Deltaflexivirus within the family Deltaflexiviridae. PoDFV2–4 had no significant effects on mycelial growth rate, plate mycelial biomass, or laccase activity. However, they significantly inhibited mycelial cellulase activity and resulted in malformed fruiting bodies, as well as a substantial reduction in yield. Full article

Heterobasidion root rot fungi represent a major threat to conifer forest stands, and virocontrol (biocontrol) has been proposed as an alternative strategy of disease management in recent years. Here, we investigated the occurrence of RNA viruses and viroid-like genomes in Heterobasidion annosum sensu lato in near-natural forests of Bosnia and Herzegovina (Dinaric Alps), a region previously unexplored in this regard. Seventeen H. annosum s.l. isolates were screened for virus presence by RNA Sequencing and bioinformatic analyses. In total, 32 distinct mycoviruses were discovered in the datasets, 26 of which were previously unknown. The detected viruses represent two dsRNA (Partitiviridae and Curvulaviridae), six linear ssRNA (Mitoviridae, Narnaviridae, Botourmiaviridae, Virgaviridae, Benyviridae, and Deltaflexiviridae) and three circular ssRNA (Dumbiviridae, Quambiviridae, and Trimbiviridae) virus families. In addition to the known circular ambiviruses with their hammerhead (HHRz) and hairpin (HPRz) ribozymes, two other smaller non-coding circular RNAs of ca. 910 bp each were identified encoding HHRz and deltavirus (DVRz) ribozymes in both polarities of their genomes. This study documents the first report of a putative viroid-like RNA agent in Heterobasidion, along with beny-like and deltaflexivirus-like viruses in Heterobasidion abietinum, and expands the known virosphere of Heterobasidion species in Southeastern European forests. Full article

Metagenomic methods are powerful tools to investigate viral diversity in biological or environmental samples and to identify previously unknown viruses. We used RNA metagenomics to identify, in the gut of red-backed voles, the nearly complete genomes of two novel members of the Kitrinoviricota, a phylum including viruses with positive-sense ssRNA genomes encoding an RNA-directed RNA polymerase. The genome of a novel member of the Tombusviridae presented four open reading frames (ORFs); a −1 frameshift is potentially involved in generating the viral replicase. This sequence was part of a phylogenetic clade that did not include any officially classified species. The second genome presented a large ORF coding for a viral polyprotein containing the typical protein domains common to flexiviruses. The sequence clustered with currently known members of the Deltaflexiviridae. Both viruses appear to represent the first members of novel species in yet undefined genera. The identified viruses likely originated from the vole diet as members of the two viral families are known to infect plants and fungi, respectively. Investigating public databases demonstrated that a much higher richness than currently recognized exists for these two viral families, highlighting the need to update taxonomy systems and possibly also include genomes identified through metagenomics. Full article

Alternaria fungus can cause notable diseases in cereals, ornamental plants, vegetables, and fruits around the world. To date, an increasing number of mycoviruses have been accurately and successfully identified in this fungus. In this study, we discovered mycoviruses from 78 strains in 6 species of the genus Alternaria, which were collected from 10 pear production areas using high-throughput sequencing technology. Using the total RNA-seq, we detected the RNA-dependent RNA polymerase of 19 potential viruses and the coat protein of two potential viruses. We successfully confirmed these viruses using reverse transcription polymerase chain reaction with RNA as the template. We identified 12 mycoviruses that were positive-sense single-stranded RNA (+ssRNA) viruses, 5 double-strand RNA (dsRNA) viruses, and 4 negative single-stranded RNA (−ssRNA) viruses. In these viruses, five +ssRNA and four −ssRNA viruses were novel mycoviruses classified into diverse the families Botourmiaviridae, Deltaflexivirus, Mymonaviridea, and Discoviridae. We identified a novel −ssRNA mycovirus isolated from an A. tenuissima strain HB-15 as Alternaria tenuissima negative-stranded RNA virus 2 (AtNSRV2). Additionally, we characterized a novel +ssRNA mycovirus isolated from an A. tenuissima strain SC-8 as Alternaria tenuissima deltaflexivirus 1 (AtDFV1). According to phylogenetic and sequence analyses, we determined that AtNSRV2 was related to the viruses of the genus Sclerotimonavirus in the family Mymonaviridae. We also found that AtDFV1 was related to the virus family Deltaflexivirus. This study is the first to use total RNA sequencing to characterize viruses in Alternaria spp. These results expand the number of Alternaria viruses and demonstrate the diversity of these mycoviruses. Full article

Various mycoviruses have been isolated from Sclerotinia sclerotiorum. Here, we identified a viral RNA sequence contig, representing a novel virus, Sclerotinia sclerotiorum deltaflexivirus 2 (SsDFV2), from an RNA_Seq database. We found that SsDFV2 was harbored in the hypovirulent strain, 228, which grew slowly on potato dextrose agar, produced a few sclerotia, and could not induce typical lesions on detached rapeseed (Brassica napus) leaves. Strain 228 was also infected by Botrytis porri RNA Virus 1 (BpRV1), a virus originally isolated from Botrytis porri. The genome of SsDFV2 comprised 6711 nucleotides, excluding the poly (A) tail, and contained a single large predicted open reading frame encoding a putative viral RNA replicase. Phylogenetic analysis demonstrated that SsDFV2 is closely related to viruses in the family Deltaflexiviridae; however, it also differs significantly from members of this family, suggesting that it may represent a new species. Further we determined that SsDFV2 could be efficiently transmitted to host vegetative incompatible individuals by dual culture. To our best knowledge, this is the first report that a (+) ssRNA mycovirus can overcome the transmission limitations of the vegetative incompatibility system, a phenomenon that may facilitate the potential use of mycoviruses for the control of crop fungal diseases. Full article