Canadian Forest Service Publications
Characterization of Cronartium ribicola dsRNAs reveals novel members of the family Totiviridae and viral association with fungal virulence. 2019. Liu, J-J., Sniezko, R.A., Schoettle, A.W. Virol J 16, 118.
Issued by: Pacific Forestry Centre
Catalog ID: 40021
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Background: Mycoviruses were recently discovered in the white pine blister rust (WPBR) fungus Cronartium ribicola (J.C. Fisch.). Detection and characterization of their double stranded RNA (dsRNA) would facilitate understanding of pathogen virulence and disease pathogenesis in WPBR systems. Methods: Full-length cDNAs were cloned from the dsRNAs purified from viral-infected C. ribicola, and their cDNA sequences were determined by DNA sequencing. Evolutionary relationships of the dsRNAs with related mycoviruses were determined by phylogenetic analysis. Dynamic distributions of the viral RNAs within samples of their fungal host C. ribicola were investigated by measurement of viral genome prevalence and viral gene expression. Results: In this study we identified and characterized five novel dsRNAs from C. ribicola, designated as Cronartium ribicola totivirus 1–5 (CrTV1 to CrTV5). These dsRNA sequences encode capsid protein and RNA-dependent RNA polymerase with significant homologies to dsRNA viruses of the family Totiviridae. Phylogenetic analysis showed that the CrTVs were grouped into two distinct clades. CrTV2 through CrTV5 clustered within the genus Totivirus. CrTV1 along with a few un-assigned dsRNAs constituted a distinct phyletic clade that is genetically distant from presently known genera in the Totiviridae family, indicating that CrTV1 represents a novel genus in the Totiviridae family. The CrTVs were prevalent in fungal samples obtained from infected western white pine, whitebark pine, and limber pines. Viral RNAs were generally expressed at higher levels during in planta mycelium growth than in aeciospores and urediniospores. CrTV4 was significantly associated with C. ribicola virulent pathotype and specific C. ribicola host tree species, suggesting dsRNAs as potential tools for dissection of pathogenic mechanisms of C. ribicola and diagnosis of C. ribicola pathotypes. Conclusion: Phylogenetic and expression analyses of viruses in the WPBR pathogen, C. ribicola, have enchanced our understanding of virus diversity in the family Totiviridae, and provided a potential strategy to utilize pathotypeassociated mycoviruses to control fungal forest diseases.
Plain Language Summary
The white pine blister rust (WPBR) fungus Cronartium ribicola (J.C. Fisch.) shows potential to be infected by mycoviruses with genomes of double stranded RNA (dsRNA). Detection and characterization of viral dsRNAs may facilitate understanding of virulence and disease pathogenesis in the WPBR systems. In this study we identified and characterized five novel dsRNAs from C. ribicola (designated as CrTV1 to CrTV5). These dsRNA sequences encode capsid protein and RNA-dependent RNA polymerase with significant homologies to the dsRNA viruses of the Totiviridae family. Phylogenetic analysis showed that CrTV2 to CrTV5 clustered with viruses of the genus Totivirus as novel members of this genus. CrTV1 along with few un-assigned dsRNAs constituted a distinct phyletic clade with genetic distances far away from all five approved and two proposed genera of the Totiviridae family, suggesting that CrTV1 may represent a new genus of the Totiviridae family. We further detected CrTV4 with a strong association with C. ribicola virulent pathotypes and host tree ranges, indicating dsRNAs as potential tools for dissection of pathogenic mechanisms of C. ribicola and diagnosis of C. ribicola pathotypes. Our findings enhance understanding of virus ecology, and provide a potential strategy to utilize pathotype-associated mycoviruses to control fungal diseases.