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G. J. Boland - One of the best experts on this subject based on the ideXlab platform.
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plant wounding and ophiostoma Mitovirus 3a omv3a influence infection of creeping bentgrass by sclerotinia homoeocarpa
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2012Co-Authors: Angela M. Orshinsky, Michael J Boehm, G. J. BolandAbstract:Abstract Colonization and lesion development by virulent, asymptomatic and hypovirulent isolates of Sclerotinia homoeocarpa on nonwounded (NW) and wounded (W) leaves of creeping bentgrass were characterized. Hypovirulent and asymptomatic isolates contain the fungal virus, Ophiostoma Mitovirus 3a, and virulent isolates are virus-free. On NW leaves, all isolates infected leaves with appressoria along cell walls and through stomata by 48 hours post-inoculation (hpi). Inter- and intracellular hyphae formed on heavily colonized, NW leaves at 96 hpi. Wound-inoculated grass had a colonization front characterized by inter- and intracellular hyphal colonization within nonsymptomatic tissues at 8 hpi by direct infection of the wound site. The colonization front grew ahead of symptom development for 50 hpi on both NW and W leaves. In contrast to virulent and asymptomatic isolates, the hypovirulent isolate seldom colonized more than 30% of leaf tissue of the NW or W leaves. Callose accumulation under fungal appressor...
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ophiostoma Mitovirus 3a ascorbic acid glutathione and photoperiod affect the development of stromata and apothecia by sclerotinia homoeocarpa
Canadian Journal of Microbiology, 2011Co-Authors: Angela M. Orshinsky, G. J. BolandAbstract:Hypovirulence in Sclerotinia homoeocarpa is associated with infection by Ophiostoma Mitovirus 3a (OMV3a). OMV3a is also present in asymptomatic isolates, with growth and virulence comparable to that of virus-free isolates. Hypo- virulent isolates have impaired mitochondrial function resulting in increased activity of the alternative oxidase pathway, which is implicated in the reduction of reactive oxygen species in other fungi. In this study, hypovirulent, asymptomatic, and virus-free isolates were grown on potato dextrose agar amended with ascorbic acid or glutathione and were incubated under various photoperiods to determine the importance of reactive oxygen species, light, and OMV3a infection for differen- tiation of stromata and apothecia by S. homoeocarpa. Hypovirulent isolates did not form stromata or apothecia. Glutathione and darkness reduced stromata size and apothecia production by virulent and asymptomatic isolates. Apothecia formed under several different photoperiods, and ascorbic acid increased apothecia production. Ascospores were not detected in these apothecia. The results suggest that hypovirulence, light, and the superoxide radical are important factors in the forma- tion of stromata and apothecia by S. homoeocarpa isolates. This is the first report of sterile apothecia production by North American isolates of S. homoeocarpa and provides a starting point for attempts to produce fertile apothecia.
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The influence of Ophiostoma Mitovirus-3a (OMV3a) on the respiration and growth of the dollar spot pathogen, Sclerotinia homoeocarpa (Bennett)
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2010Co-Authors: Angela M. Orshinsky, G. J. BolandAbstract:Abstract Sclerotinia homoeocarpa is the causal agent of dollar spot disease of turfgrass. Although both asymptomatic and hypovirulent isolates of S. homoeocarpa contain the mitochondrial virus Ophiostoma novo-ulmi Mitovirus 3a (OMV3a), only asymptomatic isolates display growth rates and virulence levels comparable to that of virus-free isolates. In this study, the respiration and growth of asymptomatic, hypovirulent and virulent isolates of S. homoeocarpa were characterized using antimycin A (AA) as a complex III inhibitor, and salicylhydroxamic acid (SHAM) as an alternative oxidase inhibitor. Results of this study indicate that alternative oxidase contributes substantially to respiration by hypovirulent isolates. All S. homoeocarpa isolates appear to utilize the alternative pathway to some extent; however, hypovirulent isolates demonstrated a substantial increase in AOX transcription relative to asymptomatic and virulent isolates. These results demonstrate that OMV3a infection interferes with the normal ...
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Attenuation of Virulence in Sclerotinia homoeocarpa during Storage is Associated with Latent Infection by Ophiostoma Mitovirus 3a
European Journal of Plant Pathology, 2006Co-Authors: F Deng, G. J. BolandAbstract:The hypovirulence-associated Mitovirus, Ophiostoma Mitovirus 3a (OMV3a), has been shown to be widespread in eastern Canadian populations of Sclerotinia homoeocarpa in the form of latent infection. Latent infection by OMV3a was not associated with an apparent phenotype and did not significantly reduce the growth and virulence of the pathogen. In the present study, we found that isolates of S. homoeocarpa latently infected by OMV3a can change to hypovirulent isolates after storage at 4 °C, and that this attenuation of virulence was associated with increased concentration of the OMV3a virus. Recurrent observations revealed that up to 29.8% of latently infected isolates changed to hypovirulent isolates after 21 months of storage. Transmission of OMV3a dsRNA from latently infected isolates to virus-free isolates resulted in latent infection of the recipient isolates, indicating that latent infection by OMV3a was not associated with genetic differences in the fungal host. The RNA genomes of the OMV3a virus in an isogenic pair of latently infected and hypovirulent isolates were sequenced and compared. Each of the two RNAs contained an open reading frame of 726 amino acids with conserved motifs typical of RNA-dependent RNA polymerase (RdRp). The OMV3a RNA sequences in these two isolates share 95.1% nucleotide and 94.6% amino acid sequence identities. The development of hypovirulence from latent infection by OMV3a virus may provide new strategies to improve the biological control efficacy of hypovirulence in dollar spot management.
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asymptomatic infection and distribution of ophiostoma Mitovirus 3a omv3a in populations of sclerotinia homoeocarpa
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2005Co-Authors: M S Melzer, F Deng, G. J. BolandAbstract:One hundred and sixteen isolates of Sclerotinia homoeocarpa from nine locations in southwestern Ontario and one location in Nova Scotia were assessed for the presence of a hypovirulence-associated Mitovirus, Ophiostoma Mitovirus 3a (OMV3a). Two detection methods, nucleic acid extraction with gel electrophoresis (NAE–GE) and reverse transcription – polymerase chain reaction (RT–PCR), were employed. Phenotype, growth rate, and virulence of isolates were also assessed. OMV3a was detected in four isolates (3.4%), using both the standard NAE–GE method and the RT–PCR method. The four isolates displayed reduced colony growth and virulence, and they were considered to be symptomatic, hypovirulent isolates infected by OMV3a. In the remaining 112 isolates, OMV3a was detected in 53 isolates by RT–PCR only. These isolates displayed typical colony growth and virulence, and they were considered to have asymptomatic infections by the virus. OMV3a was not detected by either method in 59 isolates that displayed typical co...
Kenneth W. Buck - One of the best experts on this subject based on the ideXlab platform.
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detection of an rna dependent rna polymerase in mitochondria from a Mitovirus infected isolate of the dutch elm disease fungus ophiostoma novo ulmi
Virology, 2000Co-Authors: Thomas E. Cole, Yiguo Hong, Clive M. Brasier, Kenneth W. BuckAbstract:RNA-dependent RNA polymerase (RdRp) activity has been detected in mitochondria from an isolate of Ophiostoma novo-ulmi infected with O. novo-ulmi Mitovirus 6 (OnuMV6). The reaction products corresponded to the double-stranded and single-stranded forms of OnuMV6 RNA. Western blot analysis using antibodies raised against a conserved RdRp region has detected a protein of ca. 80 kDa in OnuMV6-infected mitochondria, close to the predicted size of the OnuMV6 RdRp. No RdRp activity or protein was detected in mitochondria from an uninfected O. novo-ulmi isolate. This is the first detection of a virus RdRp in fungal mitochondria and the results are consistent with the use of UGA tryptophan codons in its synthesis.
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MULTIPLE MITOCHONDRIAL VIRUSES IN AN ISOLATE OF THE DUTCH ELM DISEASE FUNGUS OPHIOSTOMA NOVO-ULMI
Virology, 1999Co-Authors: Yiguo Hong, Sharon L Dover, Thomas E. Cole, Clive M. Brasier, Kenneth W. BuckAbstract:Abstract The nucleotide sequences of three mitochondrial virus double-stranded (ds) RNAs, RNA-4 (2599 nucleotides), RNA-5 (2474 nucleotides), and RNA-6 (2343 nucleotides), in a diseased isolate Log1/3–8d 2 (Ld) of the Dutch elm disease fungus Ophiostoma novo-ulmi have been determined. All these RNAs are A-U-rich (71–73% A + U residues). Using the fungal mitochondrial genetic code in which UGA codes for tryptophan, the positive-strand of each of RNAs 4, 5, and 6 contains a single open reading frame (ORF) with the potential to encode a protein of 783, 729, and 695 amino acids, respectively, all of which contain conserved motifs characteristic of RNA-dependent RNA polymerases (RdRps). Sequence comparisons showed that these RNAs are related to each other and to a previously characterized RNA, RNA-3a, from the same O. novo-ulmi isolate, especially within the RdRp-like motifs. However, the overall RNA nucleotide and RdRp amino acid sequence identities were relatively low (43–55% and 20–32%, respectively). The 5′- and 3′-terminal sequences of these RNAs are different, but they can all be folded into potentially stable stem-loop structures. Those of RNA-4 and RNA-6 have inverted complementarity, potentially forming panhandle structures. Their molecular and biological properties indicate that RNAs 3a, 4, 5, and 6 are the genomes of four different viruses, which replicate independently in the same cell. These four viruses are also related to a mitochondrial RNA virus from another fungus, Cryphonectria parasitica , recently designated the type species of the Mitovirus genus of the Narnaviridae family, and to a virus from the fungus Rhizoctonia solani . It is proposed that the four O. novo-ulmi mitochondrial viruses are assigned to the Mitovirus genus and designated O. novo-ulmi Mitovirus (OnuMV) 3a-Ld, 4-Ld, 5-Ld, and 6-Ld, respectively. Northern blot analysis indicated that O. novo-ulmi Ld nucleic acid extracts contain more single-stranded (ss, positive-stranded) RNA than dsRNA for all three newly described Mitoviruses. O. novo-ulmi RNA-7, previously believed to be a satellite-like RNA, is shown to be a defective RNA, derived from OnuMV4-Ld RNA by multiple internal deletions. OnuMV4-Ld is therefore the helper virus for the replication of both RNA-7 and another defective RNA, RNA-10. Sequence comparisons indicate that RNA-10 could be derived from RNA-7, as previously suggested, or derived directly from RNA-4.
F Deng - One of the best experts on this subject based on the ideXlab platform.
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Attenuation of Virulence in Sclerotinia homoeocarpa during Storage is Associated with Latent Infection by Ophiostoma Mitovirus 3a
European Journal of Plant Pathology, 2006Co-Authors: F Deng, G. J. BolandAbstract:The hypovirulence-associated Mitovirus, Ophiostoma Mitovirus 3a (OMV3a), has been shown to be widespread in eastern Canadian populations of Sclerotinia homoeocarpa in the form of latent infection. Latent infection by OMV3a was not associated with an apparent phenotype and did not significantly reduce the growth and virulence of the pathogen. In the present study, we found that isolates of S. homoeocarpa latently infected by OMV3a can change to hypovirulent isolates after storage at 4 °C, and that this attenuation of virulence was associated with increased concentration of the OMV3a virus. Recurrent observations revealed that up to 29.8% of latently infected isolates changed to hypovirulent isolates after 21 months of storage. Transmission of OMV3a dsRNA from latently infected isolates to virus-free isolates resulted in latent infection of the recipient isolates, indicating that latent infection by OMV3a was not associated with genetic differences in the fungal host. The RNA genomes of the OMV3a virus in an isogenic pair of latently infected and hypovirulent isolates were sequenced and compared. Each of the two RNAs contained an open reading frame of 726 amino acids with conserved motifs typical of RNA-dependent RNA polymerase (RdRp). The OMV3a RNA sequences in these two isolates share 95.1% nucleotide and 94.6% amino acid sequence identities. The development of hypovirulence from latent infection by OMV3a virus may provide new strategies to improve the biological control efficacy of hypovirulence in dollar spot management.
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asymptomatic infection and distribution of ophiostoma Mitovirus 3a omv3a in populations of sclerotinia homoeocarpa
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2005Co-Authors: M S Melzer, F Deng, G. J. BolandAbstract:One hundred and sixteen isolates of Sclerotinia homoeocarpa from nine locations in southwestern Ontario and one location in Nova Scotia were assessed for the presence of a hypovirulence-associated Mitovirus, Ophiostoma Mitovirus 3a (OMV3a). Two detection methods, nucleic acid extraction with gel electrophoresis (NAE–GE) and reverse transcription – polymerase chain reaction (RT–PCR), were employed. Phenotype, growth rate, and virulence of isolates were also assessed. OMV3a was detected in four isolates (3.4%), using both the standard NAE–GE method and the RT–PCR method. The four isolates displayed reduced colony growth and virulence, and they were considered to be symptomatic, hypovirulent isolates infected by OMV3a. In the remaining 112 isolates, OMV3a was detected in 53 isolates by RT–PCR only. These isolates displayed typical colony growth and virulence, and they were considered to have asymptomatic infections by the virus. OMV3a was not detected by either method in 59 isolates that displayed typical co...
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A Satellite RNA of Ophiostoma novo-ulmi Mitovirus 3a in Hypovirulent Isolates of Sclerotinia homoeocarpa.
Phytopathology, 2004Co-Authors: F Deng, G. J. BolandAbstract:Deng, F., and Boland, G. J. 2004. A satellite RNA of Ophiostoma novoulmi Mitovirus 3a in hypovirulent isolates of Sclerotinia homoeocarpa. Phytopathology 94:917-923. Two genetically distinct double-stranded RNA (dsRNA) elements were identified in hypovirulent isolates of Sclerotinia homoeocarpa, the causal agent of dollar spot of turfgrass. The large dsRNA (L-dsRNA) was consistently present in all hypovirulent isolates, whereas the small dsRNA (S-dsRNA) was found only in some hypovirulent isolates. Virulence comparisons revealed that there was no significant difference between isolates containing one or both dsRNAs. Therefore, the L-dsRNA appears to be the genetic determinant of hypovirulence, while the S-dsRNA is not essential for hypovirulence in S. homoeocarpa. The L-dsRNA in hypovirulent isolate Sh12B of S. homoeocarpa was previously characterized as a fungal mitochondrial virus and designated Ophiostoma novo-ulmi Mitovirus 3a-Sh12B (OnuMV3a-Sh12B) because it was conspecific with O. novo-ulmi Mitovirus 3a-Ld from O. novo-ulmi, the causal agent of Dutch elm disease. In the present study, the nucleotide sequences of the S-dsRNAs (738 to 767 nucleotides) in hypovirulent isolates Sh12B, Sh279B, and Sh286B were determined. Nucleotide sequence analysis indicated that the S-dsRNA was not derived from the OnuMV3a dsRNA and it could not encode an RNA-dependent RNA polymerase. These results are consistent with biological data that the S-dsRNA was always associated with the L-dsRNA and was never found independently. Therefore, the S-dsRNA can be regarded as a satellite RNA of OnuMV3a in S. homoeocarpa. Northern blotting analysis indicated that nucleic acid extracts from isolate Sh12B of S. homoeocarpa contained more single (+) stranded RNA than dsRNA for this satellite RNA. The 5′- and 3′-terminal sequences of the positive strand of the S-dsRNA each could be folded into a stem-loop structure and the terminal 21 nucleotides were complementary to each other, potentially forming a panhandle structure. Additional keyword: biological control.
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hypovirulence associated double stranded rna from sclerotinia homoeocarpa is conspecific with ophiostoma novo ulmi Mitovirus 3a ld
Phytopathology, 2003Co-Authors: F Deng, G. J. BolandAbstract:ABSTRACT The nucleotide sequence of the hypovirulence-associated double-stranded RNA (dsRNA) in hypovirulent isolate Sh12B of Sclerotinia homoeocarpa, the causal agent of dollar spot of turf grass, was determined. This large dsRNA (L-dsRNA) is 2,632 bp long and is A and U rich (61.0% A+U residues). One strand of this dsRNA contains an open reading frame (ORF) with the potential to encode a protein of 720 amino acids. This ORF contains 12 UGA codons, predicted to encode tryptophan in ascomycete mitochondria, and has a codon bias typical of mitochondrial genes, which is consistent with a mitochondrial localization of this dsRNA. The amino acid sequence contains conserved motifs typical of RNA-dependent RNA polymerases (RdRps). Sequence analyses of the nucleotide and RdRp-like protein revealed that the L-dsRNA is homologous with previously characterized mitochondrial viruses and dsRNAs from other phytopathogenic fungi, and shares 92.4% nucleotide and 95.1% amino acid sequence identities with the Ophiostoma novo-ulmi Mitovirus 3a-Ld from Ophiostoma novo-ulmi, the causal agent of Dutch elm disease. The results indicate that these two dsRNAs are conspecific. This is the first report that a hypovirulence-associated dsRNA virus naturally occurs in two taxonomically distinct fungi, and indicates that horizontal transmission of this dsRNA virus may have occurred between these fungi.
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hypovirulence associated double stranded rna from sclerotinia homoeocarpa is conspecific with ophiostoma novo ulmi Mitovirus 3a ld
Phytopathology, 2003Co-Authors: F Deng, R Xu, G. J. BolandAbstract:ABSTRACT The nucleotide sequence of the hypovirulence-associated double-stranded RNA (dsRNA) in hypovirulent isolate Sh12B of Sclerotinia homoeocarpa, the causal agent of dollar spot of turf grass, was determined. This large dsRNA (L-dsRNA) is 2,632 bp long and is A and U rich (61.0% A+U residues). One strand of this dsRNA contains an open reading frame (ORF) with the potential to encode a protein of 720 amino acids. This ORF contains 12 UGA codons, predicted to encode tryptophan in ascomycete mitochondria, and has a codon bias typical of mitochondrial genes, which is consistent with a mitochondrial localization of this dsRNA. The amino acid sequence contains conserved motifs typical of RNA-dependent RNA polymerases (RdRps). Sequence analyses of the nucleotide and RdRp-like protein revealed that the L-dsRNA is homologous with previously characterized mitochondrial viruses and dsRNAs from other phytopathogenic fungi, and shares 92.4% nucleotide and 95.1% amino acid sequence identities with the Ophiostoma n...
Yiguo Hong - One of the best experts on this subject based on the ideXlab platform.
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detection of an rna dependent rna polymerase in mitochondria from a Mitovirus infected isolate of the dutch elm disease fungus ophiostoma novo ulmi
Virology, 2000Co-Authors: Thomas E. Cole, Yiguo Hong, Clive M. Brasier, Kenneth W. BuckAbstract:RNA-dependent RNA polymerase (RdRp) activity has been detected in mitochondria from an isolate of Ophiostoma novo-ulmi infected with O. novo-ulmi Mitovirus 6 (OnuMV6). The reaction products corresponded to the double-stranded and single-stranded forms of OnuMV6 RNA. Western blot analysis using antibodies raised against a conserved RdRp region has detected a protein of ca. 80 kDa in OnuMV6-infected mitochondria, close to the predicted size of the OnuMV6 RdRp. No RdRp activity or protein was detected in mitochondria from an uninfected O. novo-ulmi isolate. This is the first detection of a virus RdRp in fungal mitochondria and the results are consistent with the use of UGA tryptophan codons in its synthesis.
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MULTIPLE MITOCHONDRIAL VIRUSES IN AN ISOLATE OF THE DUTCH ELM DISEASE FUNGUS OPHIOSTOMA NOVO-ULMI
Virology, 1999Co-Authors: Yiguo Hong, Sharon L Dover, Thomas E. Cole, Clive M. Brasier, Kenneth W. BuckAbstract:Abstract The nucleotide sequences of three mitochondrial virus double-stranded (ds) RNAs, RNA-4 (2599 nucleotides), RNA-5 (2474 nucleotides), and RNA-6 (2343 nucleotides), in a diseased isolate Log1/3–8d 2 (Ld) of the Dutch elm disease fungus Ophiostoma novo-ulmi have been determined. All these RNAs are A-U-rich (71–73% A + U residues). Using the fungal mitochondrial genetic code in which UGA codes for tryptophan, the positive-strand of each of RNAs 4, 5, and 6 contains a single open reading frame (ORF) with the potential to encode a protein of 783, 729, and 695 amino acids, respectively, all of which contain conserved motifs characteristic of RNA-dependent RNA polymerases (RdRps). Sequence comparisons showed that these RNAs are related to each other and to a previously characterized RNA, RNA-3a, from the same O. novo-ulmi isolate, especially within the RdRp-like motifs. However, the overall RNA nucleotide and RdRp amino acid sequence identities were relatively low (43–55% and 20–32%, respectively). The 5′- and 3′-terminal sequences of these RNAs are different, but they can all be folded into potentially stable stem-loop structures. Those of RNA-4 and RNA-6 have inverted complementarity, potentially forming panhandle structures. Their molecular and biological properties indicate that RNAs 3a, 4, 5, and 6 are the genomes of four different viruses, which replicate independently in the same cell. These four viruses are also related to a mitochondrial RNA virus from another fungus, Cryphonectria parasitica , recently designated the type species of the Mitovirus genus of the Narnaviridae family, and to a virus from the fungus Rhizoctonia solani . It is proposed that the four O. novo-ulmi mitochondrial viruses are assigned to the Mitovirus genus and designated O. novo-ulmi Mitovirus (OnuMV) 3a-Ld, 4-Ld, 5-Ld, and 6-Ld, respectively. Northern blot analysis indicated that O. novo-ulmi Ld nucleic acid extracts contain more single-stranded (ss, positive-stranded) RNA than dsRNA for all three newly described Mitoviruses. O. novo-ulmi RNA-7, previously believed to be a satellite-like RNA, is shown to be a defective RNA, derived from OnuMV4-Ld RNA by multiple internal deletions. OnuMV4-Ld is therefore the helper virus for the replication of both RNA-7 and another defective RNA, RNA-10. Sequence comparisons indicate that RNA-10 could be derived from RNA-7, as previously suggested, or derived directly from RNA-4.
Thomas E. Cole - One of the best experts on this subject based on the ideXlab platform.
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detection of an rna dependent rna polymerase in mitochondria from a Mitovirus infected isolate of the dutch elm disease fungus ophiostoma novo ulmi
Virology, 2000Co-Authors: Thomas E. Cole, Yiguo Hong, Clive M. Brasier, Kenneth W. BuckAbstract:RNA-dependent RNA polymerase (RdRp) activity has been detected in mitochondria from an isolate of Ophiostoma novo-ulmi infected with O. novo-ulmi Mitovirus 6 (OnuMV6). The reaction products corresponded to the double-stranded and single-stranded forms of OnuMV6 RNA. Western blot analysis using antibodies raised against a conserved RdRp region has detected a protein of ca. 80 kDa in OnuMV6-infected mitochondria, close to the predicted size of the OnuMV6 RdRp. No RdRp activity or protein was detected in mitochondria from an uninfected O. novo-ulmi isolate. This is the first detection of a virus RdRp in fungal mitochondria and the results are consistent with the use of UGA tryptophan codons in its synthesis.
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MULTIPLE MITOCHONDRIAL VIRUSES IN AN ISOLATE OF THE DUTCH ELM DISEASE FUNGUS OPHIOSTOMA NOVO-ULMI
Virology, 1999Co-Authors: Yiguo Hong, Sharon L Dover, Thomas E. Cole, Clive M. Brasier, Kenneth W. BuckAbstract:Abstract The nucleotide sequences of three mitochondrial virus double-stranded (ds) RNAs, RNA-4 (2599 nucleotides), RNA-5 (2474 nucleotides), and RNA-6 (2343 nucleotides), in a diseased isolate Log1/3–8d 2 (Ld) of the Dutch elm disease fungus Ophiostoma novo-ulmi have been determined. All these RNAs are A-U-rich (71–73% A + U residues). Using the fungal mitochondrial genetic code in which UGA codes for tryptophan, the positive-strand of each of RNAs 4, 5, and 6 contains a single open reading frame (ORF) with the potential to encode a protein of 783, 729, and 695 amino acids, respectively, all of which contain conserved motifs characteristic of RNA-dependent RNA polymerases (RdRps). Sequence comparisons showed that these RNAs are related to each other and to a previously characterized RNA, RNA-3a, from the same O. novo-ulmi isolate, especially within the RdRp-like motifs. However, the overall RNA nucleotide and RdRp amino acid sequence identities were relatively low (43–55% and 20–32%, respectively). The 5′- and 3′-terminal sequences of these RNAs are different, but they can all be folded into potentially stable stem-loop structures. Those of RNA-4 and RNA-6 have inverted complementarity, potentially forming panhandle structures. Their molecular and biological properties indicate that RNAs 3a, 4, 5, and 6 are the genomes of four different viruses, which replicate independently in the same cell. These four viruses are also related to a mitochondrial RNA virus from another fungus, Cryphonectria parasitica , recently designated the type species of the Mitovirus genus of the Narnaviridae family, and to a virus from the fungus Rhizoctonia solani . It is proposed that the four O. novo-ulmi mitochondrial viruses are assigned to the Mitovirus genus and designated O. novo-ulmi Mitovirus (OnuMV) 3a-Ld, 4-Ld, 5-Ld, and 6-Ld, respectively. Northern blot analysis indicated that O. novo-ulmi Ld nucleic acid extracts contain more single-stranded (ss, positive-stranded) RNA than dsRNA for all three newly described Mitoviruses. O. novo-ulmi RNA-7, previously believed to be a satellite-like RNA, is shown to be a defective RNA, derived from OnuMV4-Ld RNA by multiple internal deletions. OnuMV4-Ld is therefore the helper virus for the replication of both RNA-7 and another defective RNA, RNA-10. Sequence comparisons indicate that RNA-10 could be derived from RNA-7, as previously suggested, or derived directly from RNA-4.