Viral dsRNA Research Articles

Infection Defects of RNA and DNA Viruses Induced by Antiviral RNA Interference.

Immune recognition of viral genome-derived double-stranded RNA (dsRNA) molecules and their subsequent processing into small interfering RNAs (siRNAs) in plants, invertebrates, and mammals trigger specific antiviral immunity known as antiviral RNA interference (RNAi). Immune sensing of viral dsRNA is sequence-independent, and most regions of viral RNAs are targeted by virus-derived siRNAs which extensively overlap in sequence. Thus, the high mutation rates of viruses do not drive immune escape from antiviral RNAi, in contrast to other mechanisms involving specific virus recognition by host immune proteins such as antibodies and resistance (R) proteins in mammals and plants, respectively. Instead, viruses actively suppress antiviral RNAi at various key steps with a group of proteins known as viral suppressors of RNAi (VSRs). Some VSRs are so effective in virus counter-defense that potent inhibition of virus infection by antiviral RNAi is undetectable unless the cognate VSR is rendered nonexpressing or nonfunctional. Since viral proteins are often multifunctional, resistance phenotypes of antiviral RNAi are accurately defined by those infection defects of VSR-deletion mutant viruses that are efficiently rescued by host deficiency in antiviral RNAi. Here, we review and discuss in vivo infection defects of VSR-deficient RNA and DNA viruses resulting from the actions of host antiviral RNAi in model systems.

Peptidoglycan Recognition Protein S5 of Bombyx mori Facilitates the Proliferation of Bombyx mori Cypovirus 1

Bombyx mori cypovirus 1 (BmCPV1), a primary pathogen of the silkworm, is a typical dsRNA virus belonging to the Reoviridae family. In this study, a total of 2520 differentially expressed genes (DEGs) were identified by RNA-seq analysis of the silkworm midgut after BmCPV1 infection and Gene Ontology (GO) functional annotation showed that the DEGs predominantly functioned in binding (molecular function), cell (cellular component), and cellular processes (biological process). Additionally, the Kyoto Encyclopedia of Genes and Genomes (KEGG) functional annotation revealed that the DEGs were mainly distributed in global and overview metabolism maps, translation, and signal transduction. Among the identified DEGs, BmPGRP-S5 belongs to the peptidoglycan recognition protein (PGRP) family. Previous studies have revealed that PGRPs were involved in the interactions between silkworm and BmCPV1. Here, we explored the effect of BmPGRP-S5 on BmCPV1 replication and demonstrated that BmPGRP-S5 promotes the proliferation of BmCPV1 in BmN cells through overexpression or knockdown experiments. Knocking down of BmPGRP-S5 in silkworm larvae similarly promoted the proliferation of BmCPV1. Through experimental validation, we therefore determined that BmPGRP-S5 acts as a proviral host factor for BmCPV1 infection. This study clarifies the proliferation mechanism of BmCPV1 and provides new insights into the functional role of BmPGRP-S5.

An Outstandingly Rare Occurrence of Mycoviruses in Soil Strains of the Plant-Beneficial Fungi from the Genus Trichoderma and a Novel Polymycoviridae Isolate.

In fungi, viral infections frequently remain cryptic causing little or no phenotypic changes. It can indicate either a long history of coevolution or a strong immune system of the host. Some fungi are outstandingly ubiquitous and can be recovered from a great diversity of habitats. However, the role of viral infection in the emergence of environmental opportunistic species is not known. The genus of filamentous and mycoparasitic fungi Trichoderma (Hypocreales, Ascomycota) consists of more than 400 species, which mainly occur on dead wood, other fungi, or as endo- and epiphytes. However, some species are environmental opportunists because they are cosmopolitan, can establish in a diversity of habitats, and can also become pests on mushroom farms and infect immunocompromised humans. In this study, we investigated the library of 163 Trichoderma strains isolated from grassland soils in Inner Mongolia, China, and found only four strains with signs of the mycoviral nucleic acids, including a strain of T. barbatum infected with a novel strain of the Polymycoviridae and named and characterized here as Trichoderma barbatum polymycovirus 1 (TbPMV1). Phylogenetic analysis suggested that TbPMV1 was evolutionarily distinct from the Polymycoviridae isolated either from Eurotialean fungi or from the order Magnaportales. Although the Polymycoviridae viruses were also known from Hypocrealean Beauveria bassiana, the phylogeny of TbPMV1 did not reflect the phylogeny of the host. Our analysis lays the groundwork for further in-depth characterization of TbPMV1 and the role of mycoviruses in the emergence of environmental opportunism in Trichoderma. IMPORTANCE Although viruses infect all organisms, our knowledge of some groups of eukaryotes remains limited. For instance, the diversity of viruses infecting fungi-mycoviruses-is largely unknown. However, the knowledge of viruses associated with industrially relevant and plant-beneficial fungi, such as Trichoderma spp. (Hypocreales, Ascomycota), may shed light on the stability of their phenotypes and the expression of beneficial traits. In this study, we screened the library of soilborne Trichoderma strains because these isolates may be developed into bioeffectors for plant protection and sustainable agriculture. Notably, the diversity of endophytic viruses in soil Trichoderma was outstandingly low. Only 2% of 163 strains contained traces of dsRNA viruses, including the new Trichoderma barbatum polymycovirus 1 (TbPMV1) characterized in this study. TbPMV1 is the first mycovirus found in Trichoderma. Our results indicate that the limited data prevent the in-depth study of the evolutionary relationship between soilborne fungi and is worth further investigation.

Stress granules are shock absorbers that prevent excessive innate immune responses to dsRNA

Proper defense against microbial infection depends on the controlled activation of the immune system. This is particularly important for the RIG-I-like receptors (RLRs), which recognize viral dsRNA and initiate antiviral innate immune responses with the potential of triggering systemic inflammation and immunopathology. Here, we show that stress granules (SGs), molecular condensates that form in response to various stresses including viral dsRNA, play key roles in the controlled activation of RLR signaling. Without the SG nucleators G3BP1/2 and UBAP2L, dsRNA triggers excessive inflammation and immune-mediated apoptosis. In addition to exogenous dsRNA, host-derived dsRNA generated in response to ADAR1 deficiency is also controlled by SG biology. Intriguingly, SGs can function beyond immune control by suppressing viral replication independently of the RLR pathway. These observations thus highlight the multi-functional nature of SGs as cellular "shock absorbers" that converge on protecting cell homeostasis by dampening both toxic immune response and viral replication.

Prevalence and diversity of mycoviruses occurring in Chinese Lentinula edodes germplasm resource

Incidence and banding patterns of virus-like dsRNA elements in 215 Chinese genetically diverse Lentinula edodes strains collected from wide geographic distribution (or producing areas) were first investigated, and 17 viruses were identified including eight novel viruses. The results revealed a 63.3% incidence of dsRNA elements in the cultivated strains and a 67.2% incidence in the wild strains. A total of 10 distinguishable dsRNAs ranging from 0.6 to 12 kbp and 12 different dsRNA patterns were detected in the positive strains. The molecular information of these dsRNA elements was characterized, and the molecular information of the other 12 different viral sequences with (+) ssRNA genome was revealed in four L. edodes strains with complex dsRNA banding patterns. RT-PCR was also done to verify the five dsRNA viruses and 12 (+) ssRNA ones. The results presented may enrich our understanding of L. edodes virus diversity, and will promote further research on virus-host interactions. ImportanceViral infections involve complicated interactions including benign, harmful or possibly beneficial to hosts. Sometimes environment could lead to a transition in lifestyles from persistent to acute, resulting in a disease phenotype. The quality of spawn, such as the vulnerability to infection of viruses, is therefore important for mushroom production. Lentinula edodes, a wood rot basidiomycete fungus, was widely cultivated in the world for its edible and medicinal properties. In this study, the profile of dsRNA elements from Chinese genetically diverse L. edodes strains collected from wide geographic distribution or producing areas was first investigated. The molecular information of the dsRNA elements was characterized. Additionally, 12 different viral sequences with (+) ssRNA genome from four L. edodes strains with complex dsRNA banding patterns were identified. The results presented here will broaden our knowledge about mushroom viruses, and promote further studies of L. edodes production and the interaction between viruses and L. edodes.

Cryptosporidium uses CSpV1 to activate host type I interferon and attenuate antiparasitic defenses

Cryptosporidium infects gastrointestinal epithelium and is a leading cause of infectious diarrhea and diarrheal-related death in children worldwide. There are no vaccines and no fully effective therapy available for the infection. Type II and III interferon (IFN) responses are important determinants of susceptibility to infection but the role for type I IFN response remains obscure. Cryptosporidium parvum virus 1 (CSpV1) is a double-stranded RNA (dsRNA) virus harbored by Cryptosporidium spp. Here we show that intestinal epithelial conditional Ifnar1−/− mice (deficient in type I IFN receptor) are resistant to C. parvum infection. CSpV1-dsRNAs are delivered into host cells and trigger type I IFN response in infected cells. Whereas C. parvum infection attenuates epithelial response to IFN-γ, loss of type I IFN signaling or inhibition of CSpV1-dsRNA delivery can restore IFN-γ-mediated protective response. Our findings demonstrate that type I IFN signaling in intestinal epithelial cells is detrimental to intestinal anti-C. parvum defense and Cryptosporidium uses CSpV1 to activate type I IFN signaling to evade epithelial antiparasitic response.

A male-killing gene encoded by a symbiotic virus of Drosophila

In most eukaryotes, biparentally inherited nuclear genomes and maternally inherited cytoplasmic genomes have different evolutionary interests. Strongly female-biased sex ratios that are repeatedly observed in various arthropods often result from the male-specific lethality (male-killing) induced by maternally inherited symbiotic bacteria such as Spiroplasma and Wolbachia. However, despite some plausible case reports wherein viruses are raised as male-killers, it is not well understood how viruses, having much smaller genomes than bacteria, are capable of inducing male-killing. Here we show that a maternally inherited double-stranded RNA (dsRNA) virus belonging to the family Partitiviridae (designated DbMKPV1) induces male-killing in Drosophila. DbMKPV1 localizes in the cytoplasm and possesses only four genes, i.e., one gene in each of the four genomic segments (dsRNA1−dsRNA4), in contrast to ca. 1000 or more genes possessed by Spiroplasma or Wolbachia. We also show that a protein (designated PVMKp1; 330 amino acids in size), encoded by a gene on the dsRNA4 segment, is necessary and sufficient for inducing male-killing. Our results imply that male-killing genes can be easily acquired by symbiotic viruses through reassortment and that symbiotic viruses are hidden players in arthropod evolution. We anticipate that host-manipulating genes possessed by symbiotic viruses can be utilized for controlling arthropods.

Capsid structure of a fungal dsRNA megabirnavirus reveals its previously unidentified surface architecture.

Rosellinia necatrix megabirnavirus 1-W779 (RnMBV1) is a non-enveloped icosahedral double-stranded (ds)RNA virus that infects the ascomycete fungus Rosellinia necatrix, a causative agent that induces a lethal plant disease white root rot. Herein, we have first resolved the atomic structure of the RnMBV1 capsid at 3.2 Å resolution using cryo-electron microscopy (cryo-EM) single-particle analysis. Compared with other non-enveloped icosahedral dsRNA viruses, the RnMBV1 capsid protein structure exhibits an extra-long C-terminal arm and a surface protrusion domain. In addition, the previously unrecognized crown proteins are identified in a symmetry-expanded cryo-EM model and are present over the 3-fold axes. These exclusive structural features of the RnMBV1 capsid could have been acquired for playing essential roles in transmission and/or particle assembly of the megabirnaviruses. Our findings, therefore, will reinforce the understanding of how the structural and molecular machineries of the megabirnaviruses influence the virulence of the disease-related ascomycete fungus.

Melastoma malabathricum L. Suppresses Neutrophil Extracellular Trap Formation Induced by Synthetic Analog of Viral Double-Stranded RNA Associated with SARS-CoV-2 Infection.

Platelet hyper-reactivity and neutrophil extracellular trap (NET) formation contribute to the development of thromboembolic diseases for patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This study investigated the pathophysiological effects of SARS-CoV-2 surface protein components and the viral double-stranded RNA (dsRNA) on platelet aggregation and NET formation. Traditional Chinese medicine (TCM) with anti-viral effects was also delineated. The treatment of human washed platelets with SARS-CoV-2 spike protein S1 or the ectodomain S1 + S2 regions neither caused platelet aggregation nor enhanced agonists-stimulated platelet aggregation. Moreover, NET formation can be induced by polyinosinic-polycytidylic acid (poly(I:C)), a synthetic analog of viral dsRNA, but not by the pseudovirus composed of SARS-CoV-2 spike, envelope, and membrane proteins. To search for TCM with anti-NET activity, the plant Melastoma malabathricum L. which has anticoagulant activity was partially purified by fractionation. One of the fractions inhibited poly(I:C)-induced NET formation in a dose-dependent manner. This study implicates that SARS-CoV-2 structural proteins alone are not sufficient to promote NET and platelet activation. Instead, dsRNA formed during viral replication stimulates NET formation. This study also sheds new insight into using the active components of Melastoma malabathricum L. with anti-NET activity in the battle of thromboembolic diseases associated with SARS-CoV-2 infection.

Ebola virus disease: In vivo protection provided by the PAMP restricted TLR3 agonist rintatolimod and its mechanism of action

Ebola virus (EBOV) is a highly infectious and lethal pathogen responsible for sporadic self-limiting clusters of Ebola virus disease (EVD) in Central Africa capable of reaching epidemic status. 100% protection from lethal EBOV-Zaire in Balb/c mice was achieved by rintatolimod (Ampligen) at the well tolerated human clinical dose of 6 mg/kg. The data indicate that the mechanism of action is rintatolimod's dual ability to act as both a competitive decoy for the IID domain of VP35 blocking viral dsRNA sequestration and as a pathogen-associated molecular pattern (PAMP) restricted agonist for direct TLR3 activation but lacking RIG-1-like cytosolic helicase agonist properties. These data show promise for rintatolimod as a prophylactic therapy against human Ebola outbreaks.

The Impact of Variation in the Toll-like Receptor 3 Gene on Epizootic Hemorrhagic Disease in Illinois Wild White-Tailed Deer (Odocoileus virginianus).

Epizootic hemorrhagic disease (EHD) leads to high mortality in white-tailed deer (Odocoileus virginianus) and is caused by a double-stranded RNA (dsRNA) virus. Toll-like receptor 3 (TLR3) plays a role in host immune detection and response to dsRNA viruses. We, therefore, examined the role of genetic variation within the TLR3 gene in EHD among 84 Illinois wild white-tailed deer (26 EHD-positive deer and 58 EHD-negative controls). The entire coding region of the TLR3 gene was sequenced: 2715 base pairs encoding 904 amino acids. We identified 85 haplotypes with 77 single nucleotide polymorphisms (SNPs), of which 45 were synonymous mutations and 32 were non-synonymous. Two non-synonymous SNPs differed significantly in frequency between EHD-positive and EHD-negative deer. In the EHD-positive deer, phenylalanine was relatively less likely to be encoded at codon positions 59 and 116, whereas leucine and serine (respectively) were detected less frequently in EHD-negative deer. Both amino acid substitutions were predicted to impact protein structure or function. Understanding associations between TLR3 polymorphisms and EHD provides insights into the role of host genetics in outbreaks of EHD in deer, which may allow wildlife agencies to better understand the severity of outbreaks.

Synergistic Inhibitory Effect of Lactobacillus Cell Lysates and Butyrate on Poly I:C-Induced IL-8 Production in Human Intestinal Epithelial Cells.

Postbiotics include cell lysates (CLs), enzymes, cell wall fragments, and heat-killed bacteria derived from probiotics. Although postbiotics are increasingly being considered for their potential health-promoting properties, the effects of postbiotics on virus-mediated inflammatory responses in the intestine have not been elucidated. Hence, the present study aimed to examine whether CLs of Lactipantibacillus plantarum (LP CL) and Lacticaseibacillus rhamnosus GG (LR CL) could inhibit virus-mediated inflammatory responses in the human intestinal epithelial cell line HT-29 in vitro. Pretreatment with LP CL and LR CL significantly inhibited interleukin (IL)-8 production, which was induced by poly I:C, a synthetic analog of double-stranded RNA (dsRNA) viruses, at the mRNA and protein levels in HT-29 cells. However, peptidoglycans and heat-killed L. plantarum and L. rhamnosus GG did not effectively inhibit IL-8 production. LP CL and LR CL attenuated the poly I:C-induced phosphorylation of ERK and JNK and the activation of NF-κB, suggesting that these CLs could inhibit poly I:C-induced IL-8 production by regulating intracellular signaling pathways in HT-29 cells. Furthermore, among the short-chain fatty acids, butyrate enhanced the inhibitory effect of CLs on poly I:C-induced IL-8 production at the mRNA and protein levels in HT-29 cells, while acetate and propionate did not. Taken together, these results suggest that both LP CL and LR CL could act as potent effector molecules that can inhibit virus-mediated inflammatory responses and confer synergistic inhibitory effects with butyrate in human intestinal epithelial cells.

ICTV Virus Taxonomy Profile: Yadokariviridae 2023.

The family Yadokariviridae, with the genera Alphayadokarivirus and Betayadokarivirus, includes capsidless non-segmented positive-sense (+) RNA viruses that hijack capsids from phylogenetically distant double-stranded RNA viruses. Yadokarivirids likely replicate inside the hijacked heterocapsids using their own RNA-directed RNA polymerase, mimicking dsRNA viruses despite their phylogenetic placement in a (+) RNA virus lineage. Yadokarivirids can have negative or positive impacts on their host fungi, through interactions with the capsid donor dsRNA viruses. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) report on the family Yadokariviridae, which is available at ictv.global/report/yadokariviridae.

Principles of RNA recruitment to viral ribonucleoprotein condensates in a segmented dsRNA virus.

Rotaviruses transcribe 11 distinct RNAs that must be co-packaged prior to their replication to make an infectious virion. During infection, nontranslating rotavirus transcripts accumulate in cytoplasmic protein-RNA granules known as viroplasms that support segmented genome assembly and replication via a poorly understood mechanism. Here, we analysed the RV transcriptome by combining DNA-barcoded smFISH of rotavirus-infected cells. Rotavirus RNA stoichiometry in viroplasms appears to be distinct from the cytoplasmic transcript distribution, with the largest transcript being the most enriched in viroplasms, suggesting a selective RNA enrichment mechanism. While all 11 types of transcripts accumulate in viroplasms, their stoichiometry significantly varied between individual viroplasms. Accumulation of transcripts requires the presence of 3' untranslated terminal regions and viroplasmic localisation of the viral polymerase VP1, consistent with the observed lack of polyadenylated transcripts in viroplasms. Our observations reveal similarities between viroplasms and other cytoplasmic RNP granules and identify viroplasmic proteins as drivers of viral RNA assembly during viroplasm formation.

Detection of Mycovirus in Sclerotium Rolfsii, A Phytopathogenic Fungus in Bangladesh

A research project was conducted to detect presence of mycovirus, a probable virocontrol agent in Sclerotium rolfsii, a destructive soil-borne plant pathogenic fungus. A total of 500 isolates of the pathogen was isolated from infected wheat, bush bean, tomato, eggplant, lentil, chickpea, eggplant, chilli and okra grown Bangladesh following tissue planting methods and brought to the Virology laboratory of Okayama University, Japan. After brought to Japan, a total of 472 isolates were re-isolated and the fungal isolates were cultured on potato dextrose agar for extraction of DNA and dsRNA. The extracted nucleic acids were tested for the presence of viruses using rolling circle amplification (RCA) (for DNA viruses) and cellulose column chromatography (for RNA viruses). The detected S. rolfsii viruses were further characterized molecularly. For detection of DNA virus, a total of 120 isolates were tested, none were found positive for DNA viruses. For detection of dsRNA virus, a total of 472 isolates were tested, 7 isolates showed possible dsRNA positive band. The partial cDNA sequences of the dsRNA segments isolated from the strain SR336 were obtained. BlastX database search with the partial sequence from SR336 isolates showed similarities with randorna like virus. To screen the presence of randorna like virus in S. rolfsii isolates, 64 isolates were selected from 472 isolates of S. rolfsii. The isolates of S. rolfsii were tested by RT-PCR using randorna virus specific primers. Out of 64 isolates 13, (20.31%) isolates were randorna virus positive strain and rest of the isolates were absent of randorna virus.
 Bangladesh J. Agril. Res. 46(3): 331-341, September 2021

Identification of novel RNA mycoviruses from wild mushroom isolates in Japan

The characterization of viruses from environmental samples could aid in our understanding of their ecological significance and potential for biotechnological exploitation. While there has been much focus on pathogenic fungi or commercially cultivated mushrooms, attention to viruses from wild Basidiomycota mushrooms is lacking. Therefore, in this study, we conducted viral screening of fungal mycelia isolated from wild basidiocarps using agarose gel electrophoresis (AGE) and fragmented and primer-ligated dsRNA sequencing (FLDS). Among the 51 isolates, seven isolates were detected with virus-like bands during the initial screening with AGE, but only five isolates were detected with viruses after long-term storage. Using the FLDS method, we obtained seven viral genome sequences, including five double-stranded RNA (dsRNA) viruses belonging to Partitiviridae and Curvulaviridae, one positive-sense single-stranded RNA (ssRNA) virus belonging to Endornaviridae and one negative-sense ssRNA virus belonging to Tulasviridae (Bunyavirales). All viruses characterized in this study are novel species. These findings greatly expanded our knowledge of the diversity of RNA viruses from environmental samples.

Sequencing-based network analysis provides a core set of genes for understanding hemolymph immune response mechanisms against Poly I:C stimulation in Amphioctopus fangsiao

Aquatic viruses can spread rapidly and widely in seawater for their high infective ability. Polyinosinic-polycytidylic acid (Poly I:C), a viral dsRNA analog, is an immunostimulant that has been proved to activate various immune responses of immune cells in invertebrate. Hemolymph is a critical site that host immune response in invertebrates, and its transcriptome information obtained from Amphioctopus fangsiao stimulated by Poly I:C is crucial for understanding the antiviral molecular mechanisms of this species. In this study, we analyzed gene expression data in A. fangsiao hemolymph tissue within 24 h under Poly I:C stimulation and found 1082 and 299 differentially expressed genes (DEGs) at 6 and 24 h, respectively. Union set (1,369) DEGs were selected for subsequent analyses. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analyses were carried out for identifying DEGs related to immunity. Several significant immune-related terms and pathways, such as toll-like receptor signaling pathways term, inflammatory response term, TNF signaling pathway, and chemokine signaling pathway were identified. A protein–protein interaction (PPI) network was constructed for examining the relationships among immune-related genes. Finally, 12 hub genes, including EGFR, ACTG1, MAP2K1, and other nine hub genes, were identified based on the KEGG enrichment analysis and PPI network. The quantitative RT-PCR (qRT-PCR) was used to verify the expression profile of 12 hub genes. This research provides a reference for solving the problem of high mortality of A. fangsiao and other mollusks and provides a reference for the future production of some disease-resistant A. fangsiao.

Genetic Characterization of DH13M98, Umatilla Virus, Isolated from Culex tritaeniorhynchus Giles in Yunnan Province, China

Background: In August 2013, a virus strain (DH13M98) was isolated from Culex tritaeniorhynchus Giles collected in Mangshi, the southwestern border area of Yunnan Province, China. The virus replicated and caused cytopathic effects (CPE) in Aedes albopictus (C6/36) cells, but not in baby hamster Syrian kidney (BHK-21) cells. Materials and Methods: Agarose gel electrophoresis (AGE) analysis revealed that the DH13M98 virus was a 10-segment double-stranded RNA (dsRNA) virus, with a "1-1-1-2-1-1-2-1" pattern. The full genome of the DH13M98 virus was sequenced by full-length amplification of complementary DNAs (FLAC). Results: Phylogenetic analysis of the viral RNA-dependent RNA polymerase (Pol), major subcore-shell (T2), and major core-surface (T13) protein showed that DH13M98 clustered with Umatilla virus (UMAV), and the amino acid (aa) sequences of DH13M98 shared more than 89.5% (Pol), 95% (T2), and 91.1% (T13) identity with UMAV. However, the aa identity of outer capsid protein one (OC1) of DH13M98 with other UMAV was 57.1-79.2%, suggesting that DH13M98 was UMAV, but distinct from other strains of UMAV from the United States, Japan, and Germany at OC1, and it may be a high variant strain of UMAV, even a new serotype. Conclusion: This is the first isolation of UMAV in China, which enriches the resources of virus species in China and provides new insights into the genetic diversity and geographical distribution of the virus.

Molecular and biological characteristics of a novel chrysovirus infecting the fungus phytopathogenic Setosphaeria turcica f.sp. sorghi

A new double-stranded RNA (dsRNA) virus has been identified in the filamentous fungus Setosphaeria turcica f.sp. sorghi, whose genome consists of four segments (dsRNA1–4). Each dsRNA carries single open reading frame (ORF) flanked by 5′ and 3′ untranslated regions (UTRs) containing strictly conserved termini. The putative protein encoded by dsRNA1 showed 80.50% identity to the RNA-dependent RNA polymerase (RdRp) of the most closely related virus, Alternaria alternata chrysovirus 1 (AaCV1), belonging to the Chrysoviridae. dsRNA2 encodes the putative coat protein, while dsRNA3 and dsRNA4 respectively encode the hypothetical proteins of unknown functions. Phylogenetic analysis based on the RdRp protein indicated the virus clustered with members of the genus Betachrysovirus in the family Chrysoviridae. Based on the dsRNA profile, amino acid sequence comparisons, and phylogenetic analyses, the mycovirus is thought to be a new member of the family Chrysoviridae and designated as Setosphaeria turcica chrysovirus 1 (StCV1). Moreover, obvious differences were observed in the colony, mycelial and spore morphology between StCV1-infected and virus-cured strains of S. turcica f.sp. sorghi. StCV1 infection strongly reduced colony growth rate, spore production ability and virulence on host fungus. To our knowledge, this is the first report about mycovirus infecting S. turcica f.sp. sorghi and also the first chrysovirus infecting S. turcica.

Molecular characterization of a novel non-segmented double-stranded RNA mycovirus isolated from Penicillium citrinum strain RCEF7060.

Penicillium citrinum is a commonly occurring filamentous fungus with a worldwide distribution. However, no sequence data for viruses in P. citrinum have been reported. Here, we characterized a novel dsRNA virus from the hospital indoor air fungal strain P. citrinum RCEF 7060, which we have named "Penicillium citrinum non-segmented dsRNA virus 1" (PcNRV1). The genome of PcNRV1 dsRNA is 2,895bp in length and contains two open reading frames encoding a protein with an unknown function in ORF1 and a putative RNA-dependent RNA polymerase (RdRp) in ORF2. Sequence comparisons and phylogenetic analysis showed that PcNRV formed a well-supported independent clade together with members of the proposed genus "Unirnavirus" and was most closely related to Penicillium miczynskii RNA virus 1 (PmRV1), with 76.45% amino acid sequence identity in the RdRp. Thus, PcNRV1 is a novel non-segmented dsRNA mycovirus belonging to the proposed genus "Unirnavirus" and is the first characterized viral sequence from P. citrinum.