Department of Applied Microbiology, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan.
Virol J. 2012 Mar 6;9:60. doi: 10.1186/1743-422X-9-60.
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. In this study, the dsRNA genome of a mycovirus recently found in a shiitake commercial strain was sequenced and its molecular structure was characterized.
A 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.
The 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.
The results suggest that LeV represents a novel family of mycoviruses, found thus far only among the basidiomycetes.
20 世纪 70 年代，鉴定出了感染食用蘑菇香菇（香菇）的真菌病毒，但它们并未被视为蘑菇病害的病原体。它们的基因都没有被测序。在这项研究中，最近在香菇商业菌株中发现的真菌病毒的 dsRNA 基因组被测序，并对其分子结构进行了特征描述。
从香菇子实体纯化的 dsRNA 构建 cDNA 文库。该病毒被暂定命名为香菇真菌病毒 HKB（LeV）。基于推导的 RNA 依赖性 RNA 聚合酶（RdRp）序列，对 LeV 进行了系统发育分析。由于通过电子显微镜观察未观察到与 dsRNA 相关的病毒粒子，因此选择原子力显微镜（AFM）观察来实现病毒的分子成像。
获得了 LeV 的 11,282bp 基因组。该基因组编码两个开放阅读框（ORF）。ORF1 编码一个假定的蛋白质，ORF2 编码一个假定的 RdRp。此外，ORF1 中存在编码 NUDIX 结构域的区域。ORF1 和 RdRp 之间有一个 62bp 的基因间区。在整个序列中没有发现与真菌病毒的外壳蛋白相似的序列。基于假定的 RdRp 序列的系统发育分析，LeV 与担子菌 Phlebiopsis gigantea 和 Helicobasidium mompa 中发现的 dsRNA 聚为一簇。该分支与 Totiviridae 和 Chrysoviridae 家族分开。根据基因组序列的提示，AFM 显示 LeV 的结构为线性未包裹的 dsRNA。
结果表明，LeV 代表了迄今为止仅在担子菌中发现的新型真菌病毒家族。
