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Said A Ghabrial - One of the best experts on this subject based on the ideXlab platform.
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Reprint of "The Victorivirus Helminthosporium victoriae virus 190S is the primary cause of disease/hypovirulence in its natural host and a heterologous host".
Virus research, 2016Co-Authors: Wendy M Havens, Nobuhiro Suzuki, Said A GhabrialAbstract:A transmissible disease of the plant pathogenic fungus Helminthosporium victoriae, the causal agent of Victoria blight of oats, was reported more than 50 years ago. Diseased, but not normal, isolates, of H. victoriae contain two distinct viruses designated according to their sedimentation values as Victorivirus Helminthosporium victoriae virus 190S (HvV190S) and chrysovirus Helminthosporium victoriae 145S (HvV145S). Although a viral etiology of the disease was previously proposed, conclusive evidence was lacking. Here we present unequivocal evidence based on transfecting virus-free H. victoriae protoplasts with purified virus particles showing that HvV190S is essential for disease development. Furthermore, we show an expansion of the host range of HvV190S to include Cryphonectria parasitica and we also show similarity in a subset of phenotypic traits between HvV190S-infected RNA silencing deficient mutant (Δdcl-2) of C. parasitica and a strain of H. victoriae. In virulence assays on detached American chestnut branches and Red Delicious apple fruits, HvV190S-infected C. parasitica strain Δdcl-2 was markedly less virulent than wild type and virus-free Δdcl-2 C. parasitica strains. Furthermore, the hypovirulent HvV190S-infected C. parasitica Δdcl-2 strain exhibited strong antifungal activity in dual culture with the plant pathogenic fungus Sclerotinia sclerotiorum. No such inhibitory activity was observed in comparable dual cultures with wild type and virus-free Δdcl-2 C. parasitica strains. The discovery that infection with HvV190S induced a hypovirulent phenotype in a heterologous plant pathogenic host is very significant since it might be possible to convert other economically important plant pathogenic fungi to hypovirulence using HvV190S.
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the Victorivirus helminthosporium victoriae virus 190s is the primary cause of disease hypovirulence in its natural host and a heterologous host
Virus Research, 2016Co-Authors: Wendy M Havens, Nobuhiro Suzuki, Said A GhabrialAbstract:A transmissible disease of the plant pathogenic fungus Helminthosporium victoriae, the causal agent of Victoria blight of oats, was reported more than 50 years ago. Diseased, but not normal, isolates, of H. victoriae contain two distinct viruses designated according to their sedimentation values as Victorivirus Helminthosporium victoriae virus 190S (HvV190S) and chrysovirus Helminthosporium victoriae 145S (HvV145S). Although a viral etiology of the disease was previously proposed, conclusive evidence was lacking. Here we present unequivocal evidence based on transfecting virus-free H. victoriae protoplasts with purified virus particles showing that HvV190S is essential for disease development. Furthermore, we show an expansion of the host range of HvV190S to include Cryphonectria parasitica and we also show similarity in a subset of phenotypic traits between HvV190S-infected RNA silencing deficient mutant (Δdcl-2) of C. parasitica and a strain of H. victoriae. In virulence assays on detached American chestnut branches and Red Delicious apple fruits, HvV190S-infected C. parasitica strain Δdcl-2 was markedly less virulent than wild type and virus-free Δdcl-2 C. parasitica strains. Furthermore, the hypovirulent HvV190S-infected C. parasitica Δdcl-2 strain exhibited strong antifungal activity in dual culture with the plant pathogenic fungus Sclerotinia sclerotiorum. No such inhibitory activity was observed in comparable dual cultures with wild type and virus-free Δdcl-2 C. parasitica strains. The discovery that infection with HvV190S induced a hypovirulent phenotype in a heterologous plant pathogenic host is very significant since it might be possible to convert other economically important plant pathogenic fungi to hypovirulence using HvV190S.
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The Victorivirus Helminthosporium victoriae virus 190S is the primary cause of disease/hypovirulence in its natural host and a heterologous host.
Virus Research, 2015Co-Authors: Wendy M Havens, Nobuhiro Suzuki, Said A GhabrialAbstract:A transmissible disease of the plant pathogenic fungus Helminthosporium victoriae, the causal agent of Victoria blight of oats, was reported more than 50 years ago. Diseased, but not normal, isolates, of H. victoriae contain two distinct viruses designated according to their sedimentation values as Victorivirus Helminthosporium victoriae virus 190S (HvV190S) and chrysovirus Helminthosporium victoriae 145S (HvV145S). Although a viral etiology of the disease was previously proposed, conclusive evidence was lacking. Here we present unequivocal evidence based on transfecting virus-free H. victoriae protoplasts with purified virus particles showing that HvV190S is essential for disease development. Furthermore, we show an expansion of the host range of HvV190S to include Cryphonectria parasitica and we also show similarity in a subset of phenotypic traits between HvV190S-infected RNA silencing deficient mutant (Δdcl-2) of C. parasitica and a strain of H. victoriae. In virulence assays on detached American chestnut branches and Red Delicious apple fruits, HvV190S-infected C. parasitica strain Δdcl-2 was markedly less virulent than wild type and virus-free Δdcl-2 C. parasitica strains. Furthermore, the hypovirulent HvV190S-infected C. parasitica Δdcl-2 strain exhibited strong antifungal activity in dual culture with the plant pathogenic fungus Sclerotinia sclerotiorum. No such inhibitory activity was observed in comparable dual cultures with wild type and virus-free Δdcl-2 C. parasitica strains. The discovery that infection with HvV190S induced a hypovirulent phenotype in a heterologous plant pathogenic host is very significant since it might be possible to convert other economically important plant pathogenic fungi to hypovirulence using HvV190S.
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An RNA cassette from Helminthosporium victoriae virus 190S necessary and sufficient for stop/restart translation.
Virology, 2014Co-Authors: Hua Li, Max L Nibert, Wendy M Havens, Said A GhabrialAbstract:Abstract Prototype Victorivirus HvV190S employs stop/restart translation to express its RdRp from the downstream ORF in its bicistronic mRNA. The signals for this activity appear to include a predicted RNA pseudoknot directly upstream of the CP stop and RdRp start codons, which overlap in the motif AUGA. Here we used a dual-fluorescence system to further define which HvV190S sequences are important for stop/restart translation and found that the AUGA motif plus 38 nt directly upstream are both necessary and sufficient for this activity. This RNA cassette encompasses the predicted pseudoknot, and indeed substitutions that disrupted the pseudoknot disrupted the activity whereas complementary substitutions that restored the pseudoknot restored the activity. Replacement of this RNA cassette with those from other Victoriviruses with a predicted pseudoknot in comparable position also supported stop/restart translation. To our knowledge, this is the first example of stop/restart translation regulated by an RNA pseudoknot.
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Three-dimensional Structure of Victorivirus HvV190S Suggests Coat Proteins in Most Totiviruses Share a Conserved Core
PLOS Pathogens, 2013Co-Authors: Sarah E. Dunn, Giovanni Cardone, Said A Ghabrial, Max L Nibert, Hua Li, Timothy S BakerAbstract:Double-stranded (ds)RNA fungal viruses are currently assigned to six different families. Those from the family Totiviridae are characterized by nonsegmented genomes and single-layer capsids, 300–450 A in diameter. Helminthosporium victoriae virus 190S (HvV190S), prototype of recently recognized genus Victorivirus, infects the filamentous fungus Helminthosporium victoriae (telomorph: Cochliobolus victoriae), which is the causal agent of Victoria blight of oats. The HvV190S genome is 5179 bp long and encompasses two large, slightly overlapping open reading frames that encode the coat protein (CP, 772 aa) and the RNA-dependent RNA polymerase (RdRp, 835 aa). To our present knowledge, Victoriviruses uniquely express their RdRps via a coupled termination–reinitiation mechanism that differs from the well-characterized Saccharomyces cerevisiae virus L-A (ScV-L-A, prototype of genus Totivirus), in which the RdRp is expressed as a CP/RdRp fusion protein due to ribosomal frameshifting. Here, we used transmission electron cryomicroscopy and three-dimensional image reconstruction to determine the structures of HvV190S virions and two types of virus-like particles (capsids lacking dsRNA and capsids lacking both dsRNA and RdRp) at estimated resolutions of 7.1, 7.5, and 7.6 A, respectively. The HvV190S capsid is thin and smooth, and contains 120 copies of CP arranged in a “T = 2” icosahedral lattice characteristic of ScV-L-A and other dsRNA viruses. For aid in our interpretations, we developed and used an iterative segmentation procedure to define the boundaries of the two, chemically identical CP subunits in each asymmetric unit. Both subunits have a similar fold, but one that differs from ScV-L-A in many details except for a core α-helical region that is further predicted to be conserved among many other totiviruses. In particular, we predict the structures of other Victoriviruses to be highly similar to HvV190S and the structures of most if not all totiviruses including, Leishmania RNA virus 1, to be similar as well.
Nobuhiro Suzuki - One of the best experts on this subject based on the ideXlab platform.
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Novel Victorivirus from a Pakistani Isolate of Alternaria alternata Lacking a Typical Translational Stop/Restart Sequence Signature
Viruses, 2019Co-Authors: Atif Jamal, Yukiyo Sato, Sabitree Shahi, Wajeeha Shamsi, Hideki Kondo, Nobuhiro SuzukiAbstract:The family Totiviridae currently contains five genera Totivirus, Victorivirus, Leishmavirus, Trichomonasvirus, and Giardiavirus. Members in this family generally have a set of two-open reading frame (ORF) elements in their genome with the 5′-proximal ORF (ORF1) encoding a capsid protein (CP) and the 3′-proximal one (ORF2) for RNA-dependent RNA polymerase (RdRp). How the downstream open reading frames (ORFs) are expressed is genus-specific. All Victoriviruses characterized thus far appear to use the stop/restart translation mechanism, allowing for the expression of two separate protein products from bicitronic genome-sized viral mRNA, while the totiviruses use a −1 ribosomal frame-shifting that leads to a fusion product of CP and RdRp. We report the biological and molecular characterization of a novel Victorivirus termed Alternaria alternata Victorivirus 1 (AalVV1) isolated from Alternaria alternata in Pakistan. The phylogenetic and molecular analyses showed AalVV1 to be distinct from previously reported Victoriviruses. AalVV1 appears to have a sequence signature required for the −1 frame-shifting at the ORF1/2 junction region, rather than a stop/restart key mediator. By contrast, SDS–polyacrylamide gel electrophoresis and peptide mass fingerprinting analyses of purified virion preparations suggested the expression of two protein products, not a CP-RdRp fusion product. How these proteins are expressed is discussed in this study. Possible effects of infection by this virus were tested in two fungal species: A. alternata and RNA silencing proficient and deficient strains of Cryphonectria parasitica, a model filamentous fungus. AalVV1 showed symptomless infection in all of these fungal strains, even in the RNA silencing deficient C. parasitica strain.
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novel Victorivirus from a pakistani isolate of alternaria alternata lacking a typical translational stop restart sequence signature
Viruses, 2019Co-Authors: Atif Jamal, Yukiyo Sato, Sabitree Shahi, Wajeeha Shamsi, Hideki Kondo, Nobuhiro SuzukiAbstract:The family Totiviridae currently contains five genera Totivirus, Victorivirus, Leishmavirus, Trichomonasvirus, and Giardiavirus. Members in this family generally have a set of two-open reading frame (ORF) elements in their genome with the 5′-proximal ORF (ORF1) encoding a capsid protein (CP) and the 3′-proximal one (ORF2) for RNA-dependent RNA polymerase (RdRp). How the downstream open reading frames (ORFs) are expressed is genus-specific. All Victoriviruses characterized thus far appear to use the stop/restart translation mechanism, allowing for the expression of two separate protein products from bicitronic genome-sized viral mRNA, while the totiviruses use a −1 ribosomal frame-shifting that leads to a fusion product of CP and RdRp. We report the biological and molecular characterization of a novel Victorivirus termed Alternaria alternata Victorivirus 1 (AalVV1) isolated from Alternaria alternata in Pakistan. The phylogenetic and molecular analyses showed AalVV1 to be distinct from previously reported Victoriviruses. AalVV1 appears to have a sequence signature required for the −1 frame-shifting at the ORF1/2 junction region, rather than a stop/restart key mediator. By contrast, SDS–polyacrylamide gel electrophoresis and peptide mass fingerprinting analyses of purified virion preparations suggested the expression of two protein products, not a CP-RdRp fusion product. How these proteins are expressed is discussed in this study. Possible effects of infection by this virus were tested in two fungal species: A. alternata and RNA silencing proficient and deficient strains of Cryphonectria parasitica, a model filamentous fungus. AalVV1 showed symptomless infection in all of these fungal strains, even in the RNA silencing deficient C. parasitica strain.
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Reprint of "The Victorivirus Helminthosporium victoriae virus 190S is the primary cause of disease/hypovirulence in its natural host and a heterologous host".
Virus research, 2016Co-Authors: Wendy M Havens, Nobuhiro Suzuki, Said A GhabrialAbstract:A transmissible disease of the plant pathogenic fungus Helminthosporium victoriae, the causal agent of Victoria blight of oats, was reported more than 50 years ago. Diseased, but not normal, isolates, of H. victoriae contain two distinct viruses designated according to their sedimentation values as Victorivirus Helminthosporium victoriae virus 190S (HvV190S) and chrysovirus Helminthosporium victoriae 145S (HvV145S). Although a viral etiology of the disease was previously proposed, conclusive evidence was lacking. Here we present unequivocal evidence based on transfecting virus-free H. victoriae protoplasts with purified virus particles showing that HvV190S is essential for disease development. Furthermore, we show an expansion of the host range of HvV190S to include Cryphonectria parasitica and we also show similarity in a subset of phenotypic traits between HvV190S-infected RNA silencing deficient mutant (Δdcl-2) of C. parasitica and a strain of H. victoriae. In virulence assays on detached American chestnut branches and Red Delicious apple fruits, HvV190S-infected C. parasitica strain Δdcl-2 was markedly less virulent than wild type and virus-free Δdcl-2 C. parasitica strains. Furthermore, the hypovirulent HvV190S-infected C. parasitica Δdcl-2 strain exhibited strong antifungal activity in dual culture with the plant pathogenic fungus Sclerotinia sclerotiorum. No such inhibitory activity was observed in comparable dual cultures with wild type and virus-free Δdcl-2 C. parasitica strains. The discovery that infection with HvV190S induced a hypovirulent phenotype in a heterologous plant pathogenic host is very significant since it might be possible to convert other economically important plant pathogenic fungi to hypovirulence using HvV190S.
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the Victorivirus helminthosporium victoriae virus 190s is the primary cause of disease hypovirulence in its natural host and a heterologous host
Virus Research, 2016Co-Authors: Wendy M Havens, Nobuhiro Suzuki, Said A GhabrialAbstract:A transmissible disease of the plant pathogenic fungus Helminthosporium victoriae, the causal agent of Victoria blight of oats, was reported more than 50 years ago. Diseased, but not normal, isolates, of H. victoriae contain two distinct viruses designated according to their sedimentation values as Victorivirus Helminthosporium victoriae virus 190S (HvV190S) and chrysovirus Helminthosporium victoriae 145S (HvV145S). Although a viral etiology of the disease was previously proposed, conclusive evidence was lacking. Here we present unequivocal evidence based on transfecting virus-free H. victoriae protoplasts with purified virus particles showing that HvV190S is essential for disease development. Furthermore, we show an expansion of the host range of HvV190S to include Cryphonectria parasitica and we also show similarity in a subset of phenotypic traits between HvV190S-infected RNA silencing deficient mutant (Δdcl-2) of C. parasitica and a strain of H. victoriae. In virulence assays on detached American chestnut branches and Red Delicious apple fruits, HvV190S-infected C. parasitica strain Δdcl-2 was markedly less virulent than wild type and virus-free Δdcl-2 C. parasitica strains. Furthermore, the hypovirulent HvV190S-infected C. parasitica Δdcl-2 strain exhibited strong antifungal activity in dual culture with the plant pathogenic fungus Sclerotinia sclerotiorum. No such inhibitory activity was observed in comparable dual cultures with wild type and virus-free Δdcl-2 C. parasitica strains. The discovery that infection with HvV190S induced a hypovirulent phenotype in a heterologous plant pathogenic host is very significant since it might be possible to convert other economically important plant pathogenic fungi to hypovirulence using HvV190S.
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The Victorivirus Helminthosporium victoriae virus 190S is the primary cause of disease/hypovirulence in its natural host and a heterologous host.
Virus Research, 2015Co-Authors: Wendy M Havens, Nobuhiro Suzuki, Said A GhabrialAbstract:A transmissible disease of the plant pathogenic fungus Helminthosporium victoriae, the causal agent of Victoria blight of oats, was reported more than 50 years ago. Diseased, but not normal, isolates, of H. victoriae contain two distinct viruses designated according to their sedimentation values as Victorivirus Helminthosporium victoriae virus 190S (HvV190S) and chrysovirus Helminthosporium victoriae 145S (HvV145S). Although a viral etiology of the disease was previously proposed, conclusive evidence was lacking. Here we present unequivocal evidence based on transfecting virus-free H. victoriae protoplasts with purified virus particles showing that HvV190S is essential for disease development. Furthermore, we show an expansion of the host range of HvV190S to include Cryphonectria parasitica and we also show similarity in a subset of phenotypic traits between HvV190S-infected RNA silencing deficient mutant (Δdcl-2) of C. parasitica and a strain of H. victoriae. In virulence assays on detached American chestnut branches and Red Delicious apple fruits, HvV190S-infected C. parasitica strain Δdcl-2 was markedly less virulent than wild type and virus-free Δdcl-2 C. parasitica strains. Furthermore, the hypovirulent HvV190S-infected C. parasitica Δdcl-2 strain exhibited strong antifungal activity in dual culture with the plant pathogenic fungus Sclerotinia sclerotiorum. No such inhibitory activity was observed in comparable dual cultures with wild type and virus-free Δdcl-2 C. parasitica strains. The discovery that infection with HvV190S induced a hypovirulent phenotype in a heterologous plant pathogenic host is very significant since it might be possible to convert other economically important plant pathogenic fungi to hypovirulence using HvV190S.
Satoko Kanematsu - One of the best experts on this subject based on the ideXlab platform.
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differential inductions of rna silencing among encapsidated double stranded rna mycoviruses in the white root rot fungus rosellinia necatrix
Journal of Virology, 2016Co-Authors: Hajime Yaegashi, Takeo Shimizu, Satoko KanematsuAbstract:UNLABELLED: RNA silencing acts as a defense mechanism against virus infection in a wide variety of organisms. Here, we investigated inductions of RNA silencing against encapsidated double-stranded RNA (dsRNA) fungal viruses (mycoviruses), including a partitivirus (RnPV1), a quadrivirus (RnQV1), a Victorivirus (RnVV1), a mycoreovirus (RnMyRV3), and a megabirnavirus (RnMBV1) in the phytopathogenic fungus Rosellinia necatrix Expression profiling of RNA silencing-related genes revealed that a dicer-like gene, an Argonaute-like gene, and two RNA-dependent RNA polymerase genes were upregulated by RnMyRV3 or RnMBV1 infection but not by other virus infections or by constitutive expression of dsRNA in R. necatrix Massive analysis of viral small RNAs (vsRNAs) from the five mycoviruses showed that 19- to 22-nucleotide (nt) vsRNAs were predominant; however, their ability to form duplexes with 3' overhangs and the 5' nucleotide preferences of vsRNAs differed among the five mycoviruses. The abundances of 19- to 22-nt vsRNAs from RnPV1, RnQV1, RnVV1, RnMyRV3, and RnMBV1 were 6.8%, 1.2%, 0.3%, 13.0%, and 24.9%, respectively. Importantly, the vsRNA abundances and accumulation levels of viral RNA were not always correlated, and the origins of the vsRNAs were distinguishable among the five mycoviruses. These data corroborated diverse interactions between encapsidated dsRNA mycoviruses and RNA silencing. Moreover, a green fluorescent protein (GFP)-based sensor assay in R. necatrix revealed that RnMBV1 infection induced silencing of the target sensor gene (GFP gene and the partial RnMBV1 sequence), suggesting that vsRNAs from RnMBV1 activated the RNA-induced silencing complex. Overall, this study provides insights into RNA silencing against encapsidated dsRNA mycoviruses. IMPORTANCE: Encapsidated dsRNA fungal viruses (mycoviruses) are believed to replicate inside their virions; therefore, there is a question of whether they induce RNA silencing. Here, we investigated inductions of RNA silencing against encapsidated dsRNA mycoviruses (a partitivirus, a quadrivirus, a Victorivirus, a mycoreovirus, and a megabirnavirus) in Rosellinia necatrix We revealed upregulation of RNA silencing-related genes in R. necatrix infected with a mycoreovirus or a megabirnavirus but not with other viruses, which was consistent with the relatively high abundances of vsRNAs from the two mycoviruses. We also showed common and different molecular features and origins of the vsRNAs from the five mycoviruses. Furthermore, we demonstrated the activation of RNA-induced silencing complex by mycoviruses in R. necatrix Taken together, our data provide insights into an RNA silencing pathway against encapsidated dsRNA mycoviruses which is differentially induced among encapsidated dsRNA mycoviruses; that is, diverse replication strategies exist among encapsidated dsRNA mycoviruses.
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a novel Victorivirus from a phytopathogenic fungus rosellinia necatrix is infectious as particles and targeted by rna silencing
Journal of Virology, 2013Co-Authors: Sotaro Chiba, Hideki Kondo, Satoko Kanematsu, Nobuhiro SuzukiAbstract:ABSTRACT A novel Victorivirus, termed Rosellinia necatrix Victorivirus 1 (RnVV1), was isolated from a plant pathogenic ascomycete, white root rot fungus Rosellinia necatrix, coinfected with a partitivirus. The virus was molecularly and biologically characterized using the natural and experimental hosts (chestnut blight fungus, Cryphonectria parasitica). RnVV1 was shown to have typical molecular Victorivirus attributes, including a monopartite double-stranded RNA genome with two open reading frames (ORFs) encoding capsid protein (CP) and RNA-dependent RNA polymerase (RdRp), a UAAUG pentamer presumed to facilitate the coupled termination/reinitiation for translation of the two ORFs, a spherical particle structure ∼40 nm in diameter, and moderate levels of CP and RdRp sequence identity (34 to 58%) to those of members of the genus Victorivirus within the family Totiviridae. A reproducible transfection system with purified RnVV1 virions was developed for the two distinct fungal hosts. Transfection assay with purified RnVV1 virions combined with virus elimination by hyphal tipping showed that the effects of RnVV1 on the phenotype of the natural host were negligible. Interestingly, comparison of the RNA silencing-competent (standard strain EP155) and -defective (Δ dcl-2 ) strains of C. parasitica infected with RnVV1 showed that RNA silencing acted against the virus to repress its replication, which was restored by coinfection with hypovirus or transgenic expression of an RNA silencing suppressor, hypovirus p29. Phenotypic changes were observed in the Δ dcl-2 strain but not in EP155. This is the first reported study on the host range expansion of a Totiviridae member that is targeted by RNA silencing.
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appearance of mycovirus like double stranded rnas in the white root rot fungus rosellinia necatrix in an apple orchard
FEMS Microbiology Ecology, 2013Co-Authors: Hajime Yaegashi, Atsuko Sasaki, Hitoshi Nakamura, Takuo Sawahata, Yasuhiko Iwanami, Satoko KanematsuAbstract:In general, mycoviruses are transmitted through hyphal anastomosis between vegetatively compatible strains of the same fungi, and their entire intracellular life cycle within host fungi limits transmission to separate species and even to incompatible strains belonging to the same species. Based on field observations of the white root rot fungus, Rosellinia necatrix , we found two interesting phenomena concerning mycovirus epidemiology. Specifically, apple trees in an orchard were inoculated with one or two R. necatrix strains that belonged to different mycelial compatibility groups (MCGs), strains W563 (virus-free, MCG139) and NW10 (carrying a mycovirus-like double-stranded (ds) RNA element (N10), MCG442). Forty-two sub-isolates of R. necatrix , which were retrieved 2–3 years later, were all genetically identical to W563 or NW10: however, 22 of the sub-isolates contained novel dsRNAs. Six novel dsRNAs (S1-S6) were isolated: S1 was a new Victorivirus; S2, S3, and S4 were new partitiviruses; and S5 and S6 were novel viruses that could not be assigned to any known mycovirus family. N10 dsRNA was detected in three W563 sub-isolates. These findings indicated that novel mycoviruses, from an unknown source, were infecting strains W563 and NW10 of R. necatrix in the soil, and that N10 dsRNA was being transmitted between incompatible strains, NW10 to W563.
Max L Nibert - One of the best experts on this subject based on the ideXlab platform.
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An RNA cassette from Helminthosporium victoriae virus 190S necessary and sufficient for stop/restart translation.
Virology, 2014Co-Authors: Hua Li, Max L Nibert, Wendy M Havens, Said A GhabrialAbstract:Abstract Prototype Victorivirus HvV190S employs stop/restart translation to express its RdRp from the downstream ORF in its bicistronic mRNA. The signals for this activity appear to include a predicted RNA pseudoknot directly upstream of the CP stop and RdRp start codons, which overlap in the motif AUGA. Here we used a dual-fluorescence system to further define which HvV190S sequences are important for stop/restart translation and found that the AUGA motif plus 38 nt directly upstream are both necessary and sufficient for this activity. This RNA cassette encompasses the predicted pseudoknot, and indeed substitutions that disrupted the pseudoknot disrupted the activity whereas complementary substitutions that restored the pseudoknot restored the activity. Replacement of this RNA cassette with those from other Victoriviruses with a predicted pseudoknot in comparable position also supported stop/restart translation. To our knowledge, this is the first example of stop/restart translation regulated by an RNA pseudoknot.
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Three-dimensional Structure of Victorivirus HvV190S Suggests Coat Proteins in Most Totiviruses Share a Conserved Core
PLOS Pathogens, 2013Co-Authors: Sarah E. Dunn, Giovanni Cardone, Said A Ghabrial, Max L Nibert, Hua Li, Timothy S BakerAbstract:Double-stranded (ds)RNA fungal viruses are currently assigned to six different families. Those from the family Totiviridae are characterized by nonsegmented genomes and single-layer capsids, 300–450 A in diameter. Helminthosporium victoriae virus 190S (HvV190S), prototype of recently recognized genus Victorivirus, infects the filamentous fungus Helminthosporium victoriae (telomorph: Cochliobolus victoriae), which is the causal agent of Victoria blight of oats. The HvV190S genome is 5179 bp long and encompasses two large, slightly overlapping open reading frames that encode the coat protein (CP, 772 aa) and the RNA-dependent RNA polymerase (RdRp, 835 aa). To our present knowledge, Victoriviruses uniquely express their RdRps via a coupled termination–reinitiation mechanism that differs from the well-characterized Saccharomyces cerevisiae virus L-A (ScV-L-A, prototype of genus Totivirus), in which the RdRp is expressed as a CP/RdRp fusion protein due to ribosomal frameshifting. Here, we used transmission electron cryomicroscopy and three-dimensional image reconstruction to determine the structures of HvV190S virions and two types of virus-like particles (capsids lacking dsRNA and capsids lacking both dsRNA and RdRp) at estimated resolutions of 7.1, 7.5, and 7.6 A, respectively. The HvV190S capsid is thin and smooth, and contains 120 copies of CP arranged in a “T = 2” icosahedral lattice characteristic of ScV-L-A and other dsRNA viruses. For aid in our interpretations, we developed and used an iterative segmentation procedure to define the boundaries of the two, chemically identical CP subunits in each asymmetric unit. Both subunits have a similar fold, but one that differs from ScV-L-A in many details except for a core α-helical region that is further predicted to be conserved among many other totiviruses. In particular, we predict the structures of other Victoriviruses to be highly similar to HvV190S and the structures of most if not all totiviruses including, Leishmania RNA virus 1, to be similar as well.
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three dimensional structure of Victorivirus hvv190s suggests coat proteins in most totiviruses share a conserved core
PLOS Pathogens, 2013Co-Authors: Sarah E. Dunn, Giovanni Cardone, Said A Ghabrial, Max L Nibert, Hua Li, Timothy S BakerAbstract:Author(s): Dunn, Sarah E; Li, Hua; Cardone, Giovanni; Nibert, Max L; Ghabrial, Said A; Baker, Timothy S | Abstract: Double-stranded (ds)RNA fungal viruses are currently assigned to six different families. Those from the family Totiviridae are characterized by nonsegmented genomes and single-layer capsids, 300-450 A in diameter. Helminthosporium victoriae virus 190S (HvV190S), prototype of recently recognized genus Victorivirus, infects the filamentous fungus Helminthosporium victoriae (telomorph: Cochliobolus victoriae), which is the causal agent of Victoria blight of oats. The HvV190S genome is 5179 bp long and encompasses two large, slightly overlapping open reading frames that encode the coat protein (CP, 772 aa) and the RNA-dependent RNA polymerase (RdRp, 835 aa). To our present knowledge, Victoriviruses uniquely express their RdRps via a coupled termination-reinitiation mechanism that differs from the well-characterized Saccharomyces cerevisiae virus L-A (ScV-L-A, prototype of genus Totivirus), in which the RdRp is expressed as a CP/RdRp fusion protein due to ribosomal frameshifting. Here, we used transmission electron cryomicroscopy and three-dimensional image reconstruction to determine the structures of HvV190S virions and two types of virus-like particles (capsids lacking dsRNA and capsids lacking both dsRNA and RdRp) at estimated resolutions of 7.1, 7.5, and 7.6 A, respectively. The HvV190S capsid is thin and smooth, and contains 120 copies of CP arranged in a "T = 2" icosahedral lattice characteristic of ScV-L-A and other dsRNA viruses. For aid in our interpretations, we developed and used an iterative segmentation procedure to define the boundaries of the two, chemically identical CP subunits in each asymmetric unit. Both subunits have a similar fold, but one that differs from ScV-L-A in many details except for a core α-helical region that is further predicted to be conserved among many other totiviruses. In particular, we predict the structures of other Victoriviruses to be highly similar to HvV190S and the structures of most if not all totiviruses including, Leishmania RNA virus 1, to be similar as well.
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rna sequence determinants of a coupled termination reinitiation strategy for downstream open reading frame translation in helminthosporium victoriae virus 190s and other Victoriviruses family totiviridae
Journal of Virology, 2011Co-Authors: Hua Li, Max L Nibert, Wendy M Havens, Said A GhabrialAbstract:The genome-length, dicistronic mRNA of the double-stranded RNA fungal virus Helminthosporium victoriae virus 190S (genus Victorivirus, family Totiviridae) contains two long open reading frames (ORFs) that overlap in the tetranucleotide AUGA. Translation of the downstream ORF, which encodes the RNA-dependent RNA polymerase (RdRp), has been proposed to depend on ribosomal reinitiation following termination of the upstream ORF, which encodes the capsid protein. In the current study, we examined the RNA sequence determinants for RdRp translation in this virus and demonstrated that a coupled termination-reinitiation (stop-restart) strategy is indeed used. Signals for termination-reinitiation are found within a 32-nucleotide stretch of RNA immediately upstream of the AUGA motif, including a predicted pseudoknot structure. The close proximity in which this predicted structure is followed by the upstream ORF's stop codon appears to be especially important for promoting translation of the downstream ORF. The normal strong preferences for an AUG start codon and the canonical sequence context to favor translation initiation appear somewhat relaxed for the downstream ORF. Similar sequence motifs and predicted RNA structures in other Victoriviruses suggest that they all share a related stop-restart strategy for RdRp translation. Members of the genus Victorivirus thus provide new and unique opportunities for exploring the molecular mechanisms of translational coupling, which remain only partly understood in this and other systems.
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Victorivirus, a new genus of fungal viruses in the family Totiviridae
Archives of Virology, 2009Co-Authors: Said A Ghabrial, Max L NibertAbstract:The family Totiviridae comprises viruses with nonsegmented dsRNA genomes and isometric virions. A new genus, Victorivirus , has been approved for this family, named from the specific epithet of Helminthosporium victoriae, host of the type species, Helminthosporium victoriae virus 190S . Distinguishing characteristics of the 11 viruses so far assigned to this genus include infection of filamentous fungi, an apparently coupled termination–reinitiation mechanism for translating the RNA-dependent RNA polymerase as a separate product from the upstream capsid protein, and sequence-based phylogenetic grouping in a distinct clade from other family members.
Hua Li - One of the best experts on this subject based on the ideXlab platform.
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An RNA cassette from Helminthosporium victoriae virus 190S necessary and sufficient for stop/restart translation.
Virology, 2014Co-Authors: Hua Li, Max L Nibert, Wendy M Havens, Said A GhabrialAbstract:Abstract Prototype Victorivirus HvV190S employs stop/restart translation to express its RdRp from the downstream ORF in its bicistronic mRNA. The signals for this activity appear to include a predicted RNA pseudoknot directly upstream of the CP stop and RdRp start codons, which overlap in the motif AUGA. Here we used a dual-fluorescence system to further define which HvV190S sequences are important for stop/restart translation and found that the AUGA motif plus 38 nt directly upstream are both necessary and sufficient for this activity. This RNA cassette encompasses the predicted pseudoknot, and indeed substitutions that disrupted the pseudoknot disrupted the activity whereas complementary substitutions that restored the pseudoknot restored the activity. Replacement of this RNA cassette with those from other Victoriviruses with a predicted pseudoknot in comparable position also supported stop/restart translation. To our knowledge, this is the first example of stop/restart translation regulated by an RNA pseudoknot.
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Three-dimensional Structure of Victorivirus HvV190S Suggests Coat Proteins in Most Totiviruses Share a Conserved Core
PLOS Pathogens, 2013Co-Authors: Sarah E. Dunn, Giovanni Cardone, Said A Ghabrial, Max L Nibert, Hua Li, Timothy S BakerAbstract:Double-stranded (ds)RNA fungal viruses are currently assigned to six different families. Those from the family Totiviridae are characterized by nonsegmented genomes and single-layer capsids, 300–450 A in diameter. Helminthosporium victoriae virus 190S (HvV190S), prototype of recently recognized genus Victorivirus, infects the filamentous fungus Helminthosporium victoriae (telomorph: Cochliobolus victoriae), which is the causal agent of Victoria blight of oats. The HvV190S genome is 5179 bp long and encompasses two large, slightly overlapping open reading frames that encode the coat protein (CP, 772 aa) and the RNA-dependent RNA polymerase (RdRp, 835 aa). To our present knowledge, Victoriviruses uniquely express their RdRps via a coupled termination–reinitiation mechanism that differs from the well-characterized Saccharomyces cerevisiae virus L-A (ScV-L-A, prototype of genus Totivirus), in which the RdRp is expressed as a CP/RdRp fusion protein due to ribosomal frameshifting. Here, we used transmission electron cryomicroscopy and three-dimensional image reconstruction to determine the structures of HvV190S virions and two types of virus-like particles (capsids lacking dsRNA and capsids lacking both dsRNA and RdRp) at estimated resolutions of 7.1, 7.5, and 7.6 A, respectively. The HvV190S capsid is thin and smooth, and contains 120 copies of CP arranged in a “T = 2” icosahedral lattice characteristic of ScV-L-A and other dsRNA viruses. For aid in our interpretations, we developed and used an iterative segmentation procedure to define the boundaries of the two, chemically identical CP subunits in each asymmetric unit. Both subunits have a similar fold, but one that differs from ScV-L-A in many details except for a core α-helical region that is further predicted to be conserved among many other totiviruses. In particular, we predict the structures of other Victoriviruses to be highly similar to HvV190S and the structures of most if not all totiviruses including, Leishmania RNA virus 1, to be similar as well.
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Viruses of Helminthosporium (Cochlioblus) victoriae
Advances in Virus Research, 2013Co-Authors: Said A Ghabrial, Sarah E. Dunn, Hua Li, Timothy S BakerAbstract:The enigma of the transmissible disease of Helminthosporium victoriae has almost been resolved. Diseased isolates are doubly infected with two distinct viruses, the Victorivirus Helminthosporium victoriae virus 190S and the chrysovirus HvV145S. Mixed infection, however, is not required for disease development. DNA transformation experiments and transfection assays using purified HvV190S virions strongly indicate that HvV190S alone is necessary for inducing disease symptoms. HvV145, like other chrysoviruses, appears to have no effect on colony morphology. This chapter will discuss the molecular biology of the two viruses and summarize recent results of characterization of host gene products upregulated by virus infection. Furthermore, the novel structural features of HvV190S capsid will be highlighted.
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three dimensional structure of Victorivirus hvv190s suggests coat proteins in most totiviruses share a conserved core
PLOS Pathogens, 2013Co-Authors: Sarah E. Dunn, Giovanni Cardone, Said A Ghabrial, Max L Nibert, Hua Li, Timothy S BakerAbstract:Author(s): Dunn, Sarah E; Li, Hua; Cardone, Giovanni; Nibert, Max L; Ghabrial, Said A; Baker, Timothy S | Abstract: Double-stranded (ds)RNA fungal viruses are currently assigned to six different families. Those from the family Totiviridae are characterized by nonsegmented genomes and single-layer capsids, 300-450 A in diameter. Helminthosporium victoriae virus 190S (HvV190S), prototype of recently recognized genus Victorivirus, infects the filamentous fungus Helminthosporium victoriae (telomorph: Cochliobolus victoriae), which is the causal agent of Victoria blight of oats. The HvV190S genome is 5179 bp long and encompasses two large, slightly overlapping open reading frames that encode the coat protein (CP, 772 aa) and the RNA-dependent RNA polymerase (RdRp, 835 aa). To our present knowledge, Victoriviruses uniquely express their RdRps via a coupled termination-reinitiation mechanism that differs from the well-characterized Saccharomyces cerevisiae virus L-A (ScV-L-A, prototype of genus Totivirus), in which the RdRp is expressed as a CP/RdRp fusion protein due to ribosomal frameshifting. Here, we used transmission electron cryomicroscopy and three-dimensional image reconstruction to determine the structures of HvV190S virions and two types of virus-like particles (capsids lacking dsRNA and capsids lacking both dsRNA and RdRp) at estimated resolutions of 7.1, 7.5, and 7.6 A, respectively. The HvV190S capsid is thin and smooth, and contains 120 copies of CP arranged in a "T = 2" icosahedral lattice characteristic of ScV-L-A and other dsRNA viruses. For aid in our interpretations, we developed and used an iterative segmentation procedure to define the boundaries of the two, chemically identical CP subunits in each asymmetric unit. Both subunits have a similar fold, but one that differs from ScV-L-A in many details except for a core α-helical region that is further predicted to be conserved among many other totiviruses. In particular, we predict the structures of other Victoriviruses to be highly similar to HvV190S and the structures of most if not all totiviruses including, Leishmania RNA virus 1, to be similar as well.
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rna sequence determinants of a coupled termination reinitiation strategy for downstream open reading frame translation in helminthosporium victoriae virus 190s and other Victoriviruses family totiviridae
Journal of Virology, 2011Co-Authors: Hua Li, Max L Nibert, Wendy M Havens, Said A GhabrialAbstract:The genome-length, dicistronic mRNA of the double-stranded RNA fungal virus Helminthosporium victoriae virus 190S (genus Victorivirus, family Totiviridae) contains two long open reading frames (ORFs) that overlap in the tetranucleotide AUGA. Translation of the downstream ORF, which encodes the RNA-dependent RNA polymerase (RdRp), has been proposed to depend on ribosomal reinitiation following termination of the upstream ORF, which encodes the capsid protein. In the current study, we examined the RNA sequence determinants for RdRp translation in this virus and demonstrated that a coupled termination-reinitiation (stop-restart) strategy is indeed used. Signals for termination-reinitiation are found within a 32-nucleotide stretch of RNA immediately upstream of the AUGA motif, including a predicted pseudoknot structure. The close proximity in which this predicted structure is followed by the upstream ORF's stop codon appears to be especially important for promoting translation of the downstream ORF. The normal strong preferences for an AUG start codon and the canonical sequence context to favor translation initiation appear somewhat relaxed for the downstream ORF. Similar sequence motifs and predicted RNA structures in other Victoriviruses suggest that they all share a related stop-restart strategy for RdRp translation. Members of the genus Victorivirus thus provide new and unique opportunities for exploring the molecular mechanisms of translational coupling, which remain only partly understood in this and other systems.
