Abstract
Thirty unique non-host RNAs were sequenced in the cultivated fungus, Agaricus bisporus, comprising 18 viruses each encoding an RdRp domain with an additional 8 ORFans (non-host RNAs with no similarity to known sequences). Two viruses were multipartite with component RNAs showing correlative abundances and common 3′ motifs. The viruses, all positive sense single-stranded, were classified into diverse orders/families. Multiple infections of Agaricus may represent a diverse, dynamic and interactive viral ecosystem with sequence variability ranging over 2 orders of magnitude and evidence of recombination, horizontal gene transfer and variable fragment numbers. Large numbers of viral RNAs were detected in multiple Agaricus samples; up to 24 in samples symptomatic for disease and 8–17 in asymptomatic samples, suggesting adaptive strategies for co-existence. The viral composition of growing cultures was dynamic, with evidence of gains and losses depending on the environment and included new hypothetical viruses when compared with the current transcriptome and EST databases. As the non-cellular transmission of mycoviruses is rare, the founding infections may be ancient, preserved in wild Agaricus populations, which act as reservoirs for subsequent cell-to-cell infection when host populations are expanded massively through fungiculture.
Highlights
Multiple viral infections occur in many Eukaryotic organisms, animals, plants and fungi
Contig structures were confirmed by PCRs spanning the full length of the contigs and Sanger sequencing of select regions as well as RACE PCR and Sanger sequencing of the 5′ ends. These analyses revealed 30 distinct RNA molecules not found in the A. bisporus genome which ranged in size from 0.5 kb–14.5 kb (Table 1 and Supplementary Table S1)
We propose AbV16 to be a segmented virus consisting of four components: AbV16 RNA1, encoding a type II RNA dependant RNA polymerase (RdRp), AbV16 RNA2, encoding a type 1 Vmethyltransferase domain and AbV16 RNA3 and AbV16 RNA4 each of which encodes an Open Reading Frames (ORFs) with no homology to known sequences (Fig. 1)
Summary
Multiple viral infections occur in many Eukaryotic organisms, animals, plants and fungi. Multiple virus infections involve numerous interactions among the viruses themselves, the host and the environment, resulting in changes at both the molecular and population levels that can lead to a transition in life-styles from persistent to acute, resulting in a disease phenotype[12]. MVX disease is a collective name for a mixture of symptoms (fruitbody browning, fruitbody retardation and distortion) associated with 30 dsRNAs, 26 found by Grogan et al.[10], and an additional four by Eastwood et al.[23] These RNAs are assumed to be unencapsidated viral genomes as no viral particles have been observed, Romaine et al.[24], found evidence of RNA virus packaging in membrane vesicles. Different levels of the low molecular weight RNA species (>103 fold difference) have been observed in adjacent non-symptomatic and diseased A. bisporus fruitbodies attached to the same mycelial network, indicative of a spatially-separated, viral life-style transition, persistent to acute[23]
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