Abstract
BackgroundIn the 1970s, mycoviruses were identified that infected the edible mushroom Lentinula edodes (shiitake), but they were not regarded as causal agents for mushroom diseases. None of their genes has been sequenced. In this study, the dsRNA genome of a mycovirus recently found in a shiitake commercial strain was sequenced and its molecular structure was characterized.MethodsA cDNA library was constructed from a dsRNA purified from the fruiting body of L. edodes. The virus was tentatively named L. edodes mycovirus HKB (LeV). Based on the deduced RNA-dependent RNA polymerase (RdRp) sequence, phylogenetic analysis of LeV was conducted. Because no virion particles associated with the dsRNA were observed by electron microscopic observation, atomic force microscopy (AFM) observation was chosen for achieving molecular imaging of the virus.ResultsThe 11,282-bp genome of LeV was obtained. The genome encoded two open reading frames (ORFs). ORF1 coded for a hypothetical protein and ORF2 for a putative RdRp, respectively. In addition, a region coding for a NUDIX domain was present in ORF1. There was a 62-bp intergenic region between ORF1 and RdRp. Similarity with coat protein of mycoviruses was not found within the whole sequence. Based on phylogenetic analysis of the putative RdRp sequence, LeV grouped into a clade with dsRNA found in the basidiomycetes Phlebiopsis gigantea and Helicobasidium mompa. The clade was placed apart from the Totiviridae and Chrysoviridae families. As suggested from the genome sequence, AFM revealed that the structure of LeV was linear unencapsidated dsRNA.ConclusionsThe results suggest that LeV represents a novel family of mycoviruses, found thus far only among the basidiomycetes.
Highlights
In the 1970s, mycoviruses were identified that infected the edible mushroom Lentinula edodes, but they were not regarded as causal agents for mushroom diseases
ORF2 encoded a 162,240-Da protein composed of 1426 amino acids, containing the conserved motif of RNA-dependent RNA polymerase (RdRp)
Conclusions dsRNA found in a commercial strain of Lentinula edodes was sequenced
Summary
In the 1970s, mycoviruses were identified that infected the edible mushroom Lentinula edodes (shiitake), but they were not regarded as causal agents for mushroom diseases. None of their genes has been sequenced. The dsRNA genome of a mycovirus recently found in a shiitake commercial strain was sequenced and its molecular structure was characterized. In the 1970s, viruses that infect the cultivated mushroom Lentinula edodes, or shiitake, were extensively studied in Japan [1,2,3], and three morphologically distinct viruses were detected by electron microscopy [1,3]. The single dsRNA was tentatively designated as Lentinula edodes mycovirus HKB (LeV) and was sequenced
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