A novel Tuber aestivum (Vittad.) mitovirus

Abstract

Double-stranded RNA (dsRNA) viruses have been reported from major phyla of the fungal kingdom [8, 11]. Mycovirus infections have been associated with obvious disease symptoms but often remain symptomless [3, 8, 11]. Fungal viruses are known from eleven families: Barnaviridae, Birnaviridae, Chrysoviridae, Cystoviridae, Hypoviridae, Metaviridae, Narnaviridae, Partitiviridae, Reoviridae, Totiviridae and recently also Endornaviridae [1, 8, 11, 14, 15]. The simplest mycoviruses are assigned to the genera Mitovirus and Narnavirus (family Narnaviridae). Members of both genera lack coat proteins, and their linear genomes are characterized by a single open reading frame (ORF) coding for a viral RNA-dependent RNA polymerase (RdRp). Mitoviruses, in contrast to cytoplasmatic narnaviruses, seem to replicate in strict association with mitochondria [2, 8, 11, 12]. Common characteristic features of all mitochondrial viruses are 50and 30-terminal untranslated regions (UTRs) of variable length. It has been suggested that these terminal residues act as stem-loop structures for RdRp recognition and initiation of replication [3, 4]. Mitoviruses have attracted significant attention, as they trigger fungal hypovirulence and phenotypic changes such as reduced growth, sporulation and pigmentation [3–6, 13, 20]. Most mitoviruses are known from phytopathogenic fungal genera only, such as Ophiostoma, Cryphonectria, and Botrytis, and a few from Gremmeniella, Sclerotinia, Thanatephorus, Thielaviopsis, Helicobasidium and the arbuscular mycorrhizae Glomus [4–6, 11, 19–21]. The development of biological control agents against fungal pathogens using mycoviruses has attracted significant scientific attention, whereas the exploration of virus diversity in non-pathogenic fungi has been widely neglected [15, 16]. In this paper, we report the third known virus infecting the ectomycorrhizal fungus Tuber aestivum Vittad. The genome described here is the largest one known in the genus Mitovirus, and based on its host, the name Tuber aestivum mitovirus (TaMV) is proposed. Genome characteristics are highly similar to those of other known mitoviruses, including a single ORF encoding a viral RdRp as well as typical 50 and 30 UTRs.