A Novel Mycovirus That Is Related to the Human PathogenHepatitis E Virusand Rubi-Like Viruses

Abstract

Previously, we reported that three double-stranded RNA (dsRNA) segments, designated L-, M-, and SdsRNAs, were detected in Sclerotinia sclerotiorum strain Ep-1PN. Of these, the M-dsRNA segment was derived from the genomic RNA of a potexvirus-like positive-strand RNA virus, Sclerotinia sclerotiorum debilitationassociated RNA virus. Here, we present the complete nucleotide sequence of the L-dsRNA, which is 6,043 nucleotides in length, excluding the poly(A) tail. Sequence analysis revealed the presence of a single open reading frame (nucleotide positions 42 to 5936) that encodes a protein with significant similarity to the replicases of the "alphavirus-like" supergroup of positive-strand RNA viruses. A sequence comparison of the L-dsRNA-encoded putative replicase protein containing conserved methyltransferase, helicase, and RNAdependent RNA polymerase motifs showed that it has significant sequence similarity to the replicase of Hepatitis E virus, a virus infecting humans. Furthermore, we present convincing evidence that the virus-like L-dsRNA could replicate independently with only a slight impact on growth and virulence of its host. Our results suggest that the L-dsRNA from strain Ep-1PN is derived from the genomic RNA of a positive-strand RNA virus, which we named Sclerotinia sclerotiorum RNA virus L (SsRV-L). As far as we know, this is the first report of a positive-strand RNA mycovirus that is related to a human virus. Phylogenetic and sequence analyses of the conserved motifs of the RNA replicase of SsRV-L showed that it clustered with the rubi-like viruses and that it is related to the plant clostero-, beny-and tobamoviruses and to the insect omegatetraviruses. Considering the fact that these related alphavirus-like positive-strand RNA viruses infect a wide variety of organisms, these findings suggest that the ancestral positive-strand RNA viruses might be of ancient origin and/or they might have radiated horizontally among vertebrates, insects, plants, and fungi.Sclerotinia sclerotiorum is a destructive soilborne plant pathogenic fungus with a wide host range that includes more than 450 species and subspecies among 64 genera of plants (6). As an important and unique plant pathogenic fungus, the sequence of the whole genomic DNA of S. sclerotiorum has been determined (http://www.ncbi.nlm.nih.gov/sutils/genom_table.cgi?organism ϭfungi). Double-stranded RNA (dsRNA)-associated hypovirulence in S. sclerotiorum was first reported for strain 91 (5) and later reported for strain . In strain Ep-1PN, three dsRNA segments, designated L-, M-, and S-dsRNAs, with estimated sizes of 7.4, 6.4, and 1.0 kbp, respectively, were associated with hypovirulence of S. sclerotiorum (36). Of these three dsRNA segments, only M-dsRNA was consistently detected in association with the hypovirulence phenotype (36). Evidence was recently presented that the M-dsRNA was derived from the genomic RNA of a positive-strand RNA virus, Sclerotinia sclerotiorum debilitation-associated RNA virus (SsDRV) (66). Furthermore, sequence analysis of the S-d...

Viruses accumulate in aging infection centers of a fungal forest pathogen

“…The wide phylogenetic diversity of mycoviruses is reflected by their current classification into seven dsRNA families and five ssRNA families (www.ictvonline.org), and many novel taxa are awaiting description (e.g., Preisig et al, 2000;Ahn and Lee, 2001;Márquez et al, 2007;Hammond et al, 2008;Liu et al, 2009;Yu et al, 2010). Mycoviruses with RNA genomes propagate within the cytoplasm or mitochondria of their hosts and are transmitted laterally between fungal strains through anastomoses.…”

A geminivirus-related DNA mycovirus that confers hypovirulence to a plant pathogenic fungus

“…We do not know at present how or why SsHADV-1 or its ancestor lacks the MP and the intron. However, deletions or lack of CP, MP, and other genes are often found in many fungal RNA viruses (2,19,20). Thus, it is possible that there exists a common evolutionary mechanism for both RNA and DNA viruses in fungi.…”

“…Diseases caused by S. sclerotiorum cannot be controlled efficiently because no resistant cultivars are available and fungicides are difficult to deliver into canopies and soil. Hypovirulent strains of S. sclerotiorum have been isolated (16,17), and two other RNA viruses infecting the hypovirulent strain Ep-1PN were identified (18)(19)(20). In the present study, we report on a unique geminivirus-related ssDNA mycovirus that confers hypovirulence to S. sclerotiorum and thus holds the potential for use in studies on the interactions between a DNA virus and fungi, as well as for possible use in biological control of fungal diseases of important crops.…”

Fungal negative-stranded RNA virus that is related to bornaviruses and nyaviruses

“…However, considering the special environment and features of the fungal hosts, SsNSRV-1 may lack the G protein gene. Some mycoviruses, although phylogenetically related to animal or plant viruses, often lack nonessential genes, including genes for coat protein and movement protein (32)(33)(34). And fourth, there is an additional ORF VI following the L gene (ORF V), which is absent in all extant mononegaviruses.…”