A novel mitovirus from the hypogeous ectomycorrhizal fungus Tuber excavatum

Excerpt

The evolution of mycorrhizal mutualism had a profound impact on establishment of terrestrial life [19]. Fossil records indicate that the earliest land plants, which had no proper roots, were already colonized by hyphal fungi, which formed vesicles and arbuscules strikingly similar to modern vesicular-arbuscular mycorrhizas. Today, over 90% of plants form mycorrhizal associations [19]. Although saprotrophic fungi play a central role in the forest ecosystem by cycling, translocating and sequestrating decomposed material, mycorrhizal fungi render inorganic decomposed litter accessible to their plant hosts. In return for inorganics, they receive organic compounds, in particular from coniferous and deciduous trees [14, 19]. In spite of their ecological importance, ectomycorrhizal fungi have largely been ignored by virologists interested in studying mycoviruses [10, 20‐22]. Such viruses infecting a broad range of fungi may show a high degree of specialization to their hosts, since some genera exclusively infect fungi, whereas others associated with certain virus families infect multi- or unicellular organisms [10]. Mycoviruses have been reported from almost the entire range of fungal phyla [9, 15, 17] and possess single-stranded (ssRNA) genomes (genera Botrexvirus, Mycoflexivirus; families Narnaviridae, Endornaviridae, Hypoviridae) [9, 11, 12] or double-stranded (dsRNA) genomes (families Barnaviridae, Birnaviridae, Chrysoviridae, Cystoviridae, Metaviridae, Partitiviridae, Pseudoviridae, Reoviridae and Totiviridae). Members of the Birnaviridae and Cystoviridae are reported to infect fungal hosts [9, 15, 21], but they are not listed to infect fungi in the current ICTV master species list 2009 (version 9; http://​talk.​ictvonline.​org/​files/​ictv_​documents/​m/​msl/​1231.​aspx) [7, 10]. …