Viruses accumulate in aging infection centers of a fungal forest pathogen

Abstract

Fungal viruses (mycoviruses) with RNA genomes are believed to lack extracellular infective particles. These viruses are transmitted laterally among fungal strains through mycelial anastomoses or vertically via their infected spores, but little is known regarding their prevalence and patterns of dispersal under natural conditions. Here, we examined, in detail, the spatial and temporal changes in a mycovirus community and its host fungus Heterobasidion parviporum, the most devastating fungal pathogen of conifers in the Boreal forest region. During the 7-year sampling period, viruses accumulated in clonal host individuals as a result of indigenous viruses spreading within and between clones as well as novel strains arriving via airborne spores. Viral community changes produced pockets of heterogeneity within large H. parviporum clones. The appearance of novel viral infections in aging clones indicated that transient cell-to-cell contacts between Heterobasidion strains are likely to occur more frequently than what was inferred from genotypic analyses. Intraspecific variation was low among the three partitivirus species at the study site, whereas the unassigned viral species HetRV6 was highly polymorphic. The accumulation of point mutations during persistent infections resulted in viral diversification, that is, the presence of nearly identical viral sequence variants within single clones. Our results also suggest that co-infections by distantly related viral species are more stable than those between conspecific strains, and mutual exclusion may play a role in determining mycoviral communities.

Heterobasidion wood decay fungi host diverse and globally distributed viruses related to Helicobasidium mompa partitivirus V70

“…Several partial partitivirus genome sequences further support the view that Heterobasidion partitiviruses are polyphyletic and highly diverse (Ihrmark, 2001;Vainio et al, 2011bVainio et al, , 2014. It should be noted that most Heterobasidion partitiviruses were formerly known as Heterobasidion RNA viruses, but we use the new nomenclature for all of the viruses here.…”

Description and prevalence of a putative novel mycovirus within the conifer pathogen Gremmeniella abietina

“…originating from several distant locations (e.g., Europe, Siberia, USA). Within this single species (HetRV6), most of the observed differentiation seemed to be host-or geographyrelated [44], and the genetic diversity was notably high even in single forest plots [46]. Additionally, according to the available information shown in GenBank, C. parasitica bipartite mycovirus 1 is suggested to demonstrate horizontal gene transfer between fungi and mycoviruses (GenBank accession numbers KC549809 and KC549810).…”

Virus-mediated suppression of host non-self recognition facilitates horizontal transmission of heterologous viruses

“…To date, mycovirus infections have been reported to reveal various types of interaction relationships between heterologous viruses and host fungi [8, 30]. Thus discovery of new mycoviruses may provide clues for studies on ecology and evolution of viruses [31–33]. Furthermore, hypovirulence-associated mycoviruses also have potential to be used to control fungal disease [34].…”