Discovery and Community Dynamics of Novel ssRNA Mycoviruses in the Conifer Pathogen Heterobasidion parviporum

Abstract

Heterobasidion species are highly destructive basidiomycetous conifer pathogens of the Boreal forest region. Earlier studies have revealed dsRNA virus infections of families Curvulaviridae and Partitiviridae in Heterobasidion strains, and small RNA deep sequencing has also identified infections of Mitoviridae members in these fungi. In this study, the virome of Heterobasidion parviporum was examined for the first time by RNA-Seq using total RNA depleted of rRNA. This method successfully revealed new viruses representing two established (+)ssRNA virus families not found earlier in Heterobasidion: Narnaviridae and Botourmiaviridae. In addition, we identified the presence of a recently described virus group tentatively named “ambiviruses” in H. parviporum. The H. parviporum isolates included in the study originated from experimental forest sites located within 0.7 km range from each other, and a population analysis including 43 isolates was conducted at one of the experimental plots to establish the prevalence of the newly identified viruses in clonally spreading H. parviporum individuals. Our results indicate that viral infections are considerably more diverse and common among Heterobasidion isolates than known earlier and include ssRNA viruses with high prevalence and interspecies variation.

Molecular characterization of a ssRNA mycovirus isolated from the forest pathogenic fungus Armillaria ostoyae

“…Further research on the dsRNA viruses in Armillaria spp. proceeded in the Czech Republic with no success (11) and that is in agreement with later studies showing that viruses infecting Armillaria belong to the ssRNA viruses (4,5).…”

“…Since the first description of fungal virus in cultivated mushrooms (2), dozens of new mycoviruses were identified and placed into a taxonomic system of viruses (3). Mycovirus infections are symptomless and persist inside their host for decades (4). However, instead of classical molecular methods for the identification of mycoviruses in fungal genomes, the transcriptome approaches have become more popular.…”

High Diversity of Novel Viruses in the Tree Pathogen Phytophthora castaneae Revealed by High-Throughput Sequencing of Total and Small RNA

“…“Orfanplasmoviruses” have been discovered in the virome associated with the downy mildew Pl. viticola ( Chiapello et al, 2020 ) and in the conifer fungal pathogen Heterobasidion parviporum ( Sutela et al, 2021 ). In some narnaviruses, negative-sense coding ORFs were observed (rORFs; DeRisi et al, 2019 ; Dinan et al, 2020 ).…”

“…In addition, ssRNA viruses could potentially go undetected as the replication of intermediate dsRNA may not accumulate sufficiently during cell infection to allow detection. This is likely to be the case in Heterobasidion parviporum Niemelä & Korhonen infected by viruses from two (+)ssRNA virus families Narnaviridae and Botourmiaviridae , detected by HTS of total RNA depleted of rRNA, but not discovered earlier by extensive dsRNA screening ( Sutela et al, 2021 ). Likewise, in three different species of Armillaria (Fr.)…”

Diversity and impact of single-stranded RNA viruses in CzechHeterobasidionpopulations

“…So far, 21 different partitiviruses have been described in Heterobasidion spp. and all belong to the Alphapartitivirus or Betapartitivirus genera (Sutela et al 2021). Mitoviruses ( Mitoviridae family) were detected by small RNA deep sequencing and RNA-Seq in Heterobasidion parviporum and H. annosum (Vainio et al 2015a; Vainio 2019).…”