Canadian Forest Service Publications

Characterization of Five Novel Mitoviruses in the White Pine Blister Rust Fungus Cronartium ribicola. 2016. Liu, J-J.; Chan, D.; Xiang, Y.; Williams, H.; Li, X-R.; Sniezko, R. A.; Sturrock, R.N. PLoS ONE 11(5): e0154267.

Year: 2016

Available from: Pacific Forestry Centre

Catalog ID: 36928

Language: English

CFS Availability: PDF (download)

Available from the Journal's Web site.
DOI: 10.1371/journal.pone.0154267

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Abstract

The white pine blister rust (WPBR) fungus Cronartium ribicola (J.C. Fisch.) is an exotic invasive forest pathogen causing severe stem canker disease of native white pine trees (subgenus Strobus) in North America. The present study reports discovery of five novel mitoviruses in C. ribicola by deep RNA sequencing. The complete genome of each mitovirus was determined by rapid amplification of cDNA ends (RACE) and reverse transcriptase- polymerase chain reaction (RT-PCR). A single open reading frame (ORF) encoding a putative RNA-dependent RNA polymerase (RdRp) was detected in each of the viral genomes using mitochondrial genetic codes. Phylogenetic analysis indicated that the C. ribicola mitoviruses (CrMV1 to CrMV5) are new putative species of the genus Mitovirus. qRT-PCR and RNA-Seq analyses revealed that viral RNAs were significantly increased in fungal mycelia in cankered pine stems compared to expression during two different stages of spore development, suggesting that viral genome replication and transcription benefit from active growth of the host fungus. CrMVs were widespread with relatively high levels of minor allele frequency (MAF) in western North America. As the first report of mitoviruses in the Class Pucciniomycetes, this work allows further investigation of the dynamics of a viral community in the WPBR pathosystem, including potential impacts that may affect pathogenicity and virulence of the host fungus.

Plain Language Summary

The white pine blister rust (WPBR) fungus Cronartium ribicola (J.C. Fisch.) is an exotic invasive pathogen causing severe stem canker disease of native white pine trees (the subgenus Strobus) in North America. Fungal viruses are potential agents for control of pathogenic fungi. To search for viral agent with potential application in the WPBR management, the present study reports discovery of novel fungal viruses in C. ribicola using deep mRNA sequencing technology. We determined genomic sequences of five mitoviruses, each contained a complete open reading frame (ORF) encoding a putative RNA dependent RNA polymerases (RdRp) using mitochondrial genetic codes. We performed analyses of protein sequence alignment and phylogenetics of RdRp proteins, and found that C. ribicola mitoviruses (CrMV1 to CrMV5) are new species of the genus Mitovirus (family Narnaviridae). These viruses were widely distributed in tested fungal isolates collected from British Columbia and Oregon. Viral abundance was significantly increased at fungal mycelium growth stage in infected white pine stems than at spore stages, suggesting viral genome replication and transcription benefit from active growth of the fungus host. As the first report of fungal viruses in C. ribicola, this work allows further to investigate dynamics of viral community in the WPBR pathosystem, as well as to explore fungal viruses for control of forest diseases.

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