Molecular characterization of the largest mycoviral-like double-stranded RNAs associated with Amasya cherry disease, a disease of presumed fungal aetiology

Abstract

The sequence of the four large (L) double-stranded RNAs (dsRNAs) associated with Amasya cherry disease (ACD), which has a presumed fungal aetiology, is reported. ACD L dsRNAs 1 (5121 bp) and 2 (5047 bp) potentially encode proteins of 1628 and 1620 aa, respectively, that are 37 % identical and of unknown function. ACD L dsRNAs 3 (4458 bp) and 4 (4303 bp) potentially encode proteins that are 68 % identical and contain the eight motifs conserved in RNA-dependent RNA polymerases (RdRp) of dsRNA mycoviruses, having highest similarity with those of members of the family Totiviridae. Both terminal regions share extensive conservation in all four RNAs, suggesting a functional relationship between them. As ACD L dsRNAs 1 and 2 do not encode RdRps, both are probably replicated by those from either ACD L dsRNA 3 or 4. Partial characterization of the equivalent L dsRNAs 3 and 4 associated with cherry chlorotic rusty spot revealed essentially identical sequences.

Evolutionary genomics of mycovirus-related dsRNA viruses reveals cross-family horizontal gene transfer and evolution of diverse viral lineages

“…Its genome encompasses four segments but all of which are much larger than those of chrysoviruses (Figure 4). Interestingly, the genome of Amasya cherry disease-associated mycovirus (ACDAV) also encompasses four segments but two of which putatively encode RdRps that are related to each other [36] and which cluster with RnQV1 in the phylogenetic tree (Figure 3). It has been suggested that the two RdRps of ACDAV might derive from two related viruses [35].…”

A novel mycovirus from Aspergillus fumigatus contains four unique dsRNAs as its genome and is infectious as dsRNA

“…The more abundant mycoviruses with double-stranded RNA (dsRNA) genomes are generally classified into five major families: Totiviridae (nonsegmented, 4.6-7 kbp), Partitiviridae (2 segments, 1.4-2.3 kbp), Chrysoviridae (4 segments, 2.4-3.6 kbp), Reoviridae (10-12 segments, 0.7-5 kbp), all of which are conventionally encapsidated, Megabirnaviridae (2 segments, 7-9 kbp), and the proposed families "Quadriviridae" (4 segments, 3.7-4.9 kbp) and "Alternaviridae" (4 segments, 1.4-3.6 kbp) (1)(2)(3)(4)(5)(6)(7)(8). The remaining six families (Alphaflexiviridae, Barnaviridae, Endornaviridae, Gammaflexiviridae, Hypoviridae, and Narnaviridae) accommodate single-stranded RNA (ssRNA) genomes, of which only three families (Alphaflexiviridae, Barnaviridae, and Gammaflexiviridae) form virus particles, whereas members of the remaining three virus families are unencapsidated and do not form typical virions.…”

The Enigma of Double-stranded RNA (dsRNA) Associated with Mushroom Virus X (MVX)

“…However, the sequences of other novel dsRNAs (L1 and L2) do not code for RdRPs and thus justify the novel status of these viruses until their mode of replication and relationships with L3 and L4 DsRNAs are fully established. We have aligned our sequences obtained on RdRp translations of the dsRNA (size), which show similarity to those of the published sequences (Kozlakidis et al, 2006). Interestingly, BLASTn alignments of deduced RdRP (RNA dependent RNA Polymerase) sequences of MVX-mushroom dsRNAs exhibited highest similarity also with RdRPs of PRD1 phage (host: Salmonella typhimurium), fowl plague virus and to those of dsRNA carrying Cryptosporidium baileyi (poultry biotype), some of which are known to occur in chicken litter, an ingredient of the compost for mushroom cultivation.…”

“…It may be worthwhile to overview our findings to those of the new viruses with presumed fungal aetiology such as the Amasya cherry disease. Dr Bob Coutts group at the Imperial College, London, (Kozlakidis et al, 2006) recently achieved molecular characterization of two new viruses via sequencing of two largest (novel) dsRNAs (L3, L4) of ACD whose translated RNA dependent RNA polymerase (RdRP) regions had high similarity with other members of the Totoviridae. However, the sequences of other novel dsRNAs (L1 and L2) do not code for RdRPs and thus justify the novel status of these viruses until their mode of replication and relationships with L3 and L4 DsRNAs are fully established.…”

“…For example, in plants, two cherry diseases viz., the Amasya Cherry Disease (ACD) and Cherry Chlorotic Rusty Disease (CCRD) observed in Italy or Turkey, are two recent disorders that are likely to be of fungal aetiology, but are also concurrently associated with complex pattern of mycoviral like 10-12 dsRNAs Covelli et al, 2004). Further studies by the group (Kozlakidis et al, 2006) revealed that while the larger dsRNAs carrying deduced RNA dependent RNA Polymerase (RDRP) sequences (responsible for replication process) are homologous to others in Totoviridae group, their relationships either to and the sequences of the smaller dsRNAs and of their role in replication details are not fully decoded, rendering at present, these viruses as novel.…”