Four distinct isolates of a novel polymycovirus identified in Setosphaeria turcicaZheng, Yun; Chen, Miaomiao; Li, Xiquan; Dai, Fei; Gao, Zhongnan; Deng, Qingchao; Fang, Shouguo; Zhang, Songbai; Pan, Shouhui
doi: 10.1007/s00705-023-05819-1pmid: 37351692
Isolation and analysis of double-stranded RNA (dsRNA) from the phytopathogenic fungus Setosphaeria turcica f. sp. zeae revealed the presence of a new double-stranded RNA (dsRNA) virus, tentatively named "Setosphaeria turcica polymycovirus 2" (StPmV2). The genome of StPmV2 consists of five segments (dsRNA1-5), ranging in size from 965 bp to 2462 bp. Each dsRNA contains one open reading frame (ORF) flanked by 5' and 3' untranslated regions (UTRs) with conserved terminal sequences. The putative protein encoded by dsRNA1 shows 64.52% amino acid sequence identity to the RNA-dependent RNA polymerase (RdRp) of the most closely related virus, Cladosporium cladosporioides virus 1, which belongs to the family Polymycoviridae. dsRNAs 2-4 encode the putative coat protein, methyltransferase (MTR), and proline-alanine-serine-rich protein (PASrp), respectively, and dsRNA5 encodes a protein of unknown function. Phylogenetic analysis based on the RdRp protein indicated that StPmV2 clustered with members of the family Polymycoviridae and is therefore a new mycovirus belonging to the genus Polymycovirus in the family Polymycoviridae. In addition, three other distinct isolates of StPmV2 were identified: one isolated from S. turcica f. sp. zeae and two from S. turcica f. sp. sorghi. To our knowledge, this is the first report of a polymycovirus infecting both S. turcica f. sp. zeae and S. turcica f. sp. sorghi.
Developments in the classification and nomenclature of arthropod-infecting large DNA viruses that contain pif genesvan Oers, Monique M.; Herniou, Elisabeth A.; Jehle, Johannes A.; Krell, Peter J.; Abd-Alla, Adly M.M.; Ribeiro, Bergmann M.; Theilmann, David A.; Hu, Zhihong; Harrison, Robert L.
doi: 10.1007/s00705-023-05793-8pmid: 37322175
Viruses of four families of arthropod-specific, large dsDNA viruses (the nuclear arthropod large DNA viruses, or NALDVs) possess homologs of genes encoding conserved components involved in the baculovirus primary infection mechanism. The presence of such homologs encoding per os infectivity factors (pif genes), along with their absence from other viruses and the occurrence of other shared characteristics, suggests a common origin for the viruses of these families. Therefore, the class Naldaviricetes was recently established, accommodating these four families. In addition, within this class, the ICTV approved the creation of the order Lefavirales for three of these families, whose members carry homologs of the baculovirus genes that code for components of the viral RNA polymerase, which is responsible for late gene expression. We further established a system for the binomial naming of all virus species in the order Lefavirales, in accordance with a decision by the ICTV in 2019 to move towards a standardized nomenclature for all virus species. The binomial species names for members of the order Lefavirales consist of the name of the genus to which the species belongs (e.g., Alphabaculovirus), followed by a single epithet that refers to the host species from which the virus was originally isolated. The common names of viruses and the abbreviations thereof will not change, as the format of virus names lies outside the remit of the ICTV.
Two novel flavi-like viruses shed light on the plant-infecting koshovirusesDebat, Humberto; Bejerman, Nicolás
doi: 10.1007/s00705-023-05813-7pmid: 37338667
The family Flaviviridae is composed of viruses with a positive-sense single-stranded RNA genome and includes viruses that are important veterinary and human pathogens. Most members of the family are arthropod- and vertebrate-infecting viruses, but more recently, divergent flavi-like viruses have been identified in marine invertebrate and vertebrate hosts. The striking discovery of gentian Kobu-sho-associated virus (GKaV), along with a recent report of a related virus from carrot, has expanded the known host range of flavi-like viruses to plants, suggesting they could be grouped in a proposed genus tentatively named “Koshovirus”. Here, we report the identification and characterization of two novel RNA viruses that show a genetic and evolutionary relationship to the previously identified “koshoviruses”. Their genome sequences were obtained from transcriptomic datasets of the flowering plants Coptis teeta and Sonchus asper. These two new viruses, which we have named "coptis flavi-like virus 1" (CopFLV1) and "sonchus flavi-like virus 1" (SonFLV1), are members of novel species characterized by the longest monopartite RNA genome observed so far among plant-associated RNA viruses, which is ca. 24 kb in size. Structural and functional annotations of the polyproteins of all koshoviruses resulted in the detection not only of the expected helicase and RNA-dependent RNA polymerase but also of several additional divergent domains, including AlkB oxygenase, trypsin-like serine protease, methyltransferase, and envelope E1 flavi-like domains. Phylogenetic analysis showed that CopFLV1, SonFLV1, GKaV, and the carrot flavi-like virus were grouped together in a monophyletic clade, strongly supporting the recent proposal for creation of the genus “Koshovirus” for the group of related plant-infecting flavi-like viruses.
Novel ollusvirus detected in a solitary wild bee species (Osmia taurus) in JapanTakemae, Hitoshi; Nunomura, Yuka; Yokota, Tomoko; Oba, Mami; Mizutani, Tetsuya; Hsu, Wei-Li; Sakamoto, Yoshiko
doi: 10.1007/s00705-023-05805-7pmid: 37318627
Pathogens of wild bees in Japan remain largely unknown. We examined viruses harbored by solitary wild Osmia bees, including Osmia cornifrons and Osmia taurus. Interestingly, the full-length genome of a novel virus (designated as "Osmia-associated bee chuvirus", OABV) was identified in three Osmia taurus bees collected in Fukushima prefecture. The sequences and genomic features are similar to those of Scaldis River bee virus. Phylogenetic analysis based on RNA-dependent RNA polymerase, glycoprotein, and nucleoprotein sequences showed that OABV formed a subcluster within ollusviruses and was closely related to strains identified in European countries. This study extends our knowledge of wild bee parasites in Japan.
A novel mitovirus isolated fromthe filamentous fungus Hypoxylon fendleriLi, Xiang; Ding, Fang; Zeng, Lina; Liu, Lili; Liu, Hongmei; Zhang, Tingting
doi: 10.1007/s00705-023-05811-9pmid: 37392345
Members of the fungal genus Hypoxylon of the family Xylariaceae are known to produce secondary metabolites with significant chemical diversity. There are more than 200 species in the genus, including the filamentous fungus Hypoxylon fendleri. To the best of our knowledge, there have been no reports of mycoviruses in H. fendleri. In this study, a novel mycovirus, designated “Hypoxylon fendleri mitovirus 1” (HfMV1), was isolated from this fungus. The genome of HfMV1 is 2850 nt in length with a G + C content of 36% and contains a large open reading frame (ORF) encoding an RNA-dependent RNA polymerase (RdRp). BLASTp analysis revealed that the RdRp domain of HfMV1 had 28.30–50.90% sequence identity to those of members of the genus Duamitovirus and had the highest identity (50.90%) to Fusarium graminearum mitovirus 2-2 (FgMV2-2). Phylogenetic analysis further indicated that HfMV1 is a member of the genus Duamitovirus of the family Mitoviridae. This is the first report of a mycovirus in H. fendleri.
Geminiviral betasatellites: critical viral ammunition to conquer plant immunityKumar, Sunil; Gupta, Neha; Chakraborty, Supriya
doi: 10.1007/s00705-023-05776-9pmid: 37386317
Geminiviruses have mastered plant cell modulation and immune invasion to ensue prolific infection. Encoding a relatively small number of multifunctional proteins, geminiviruses rely on satellites to efficiently re-wire plant immunity, thereby fostering virulence. Among the known satellites, betasatellites have been the most extensively investigated. They contribute significantly to virulence, enhance virus accumulation, and induce disease symptoms. To date, only two betasatellite proteins, βC1, and βV1, have been shown to play a crucial role in virus infection. In this review, we offer an overview of plant responses to betasatellites and counter-defense strategies deployed by betasatellites to overcome those responses.