Nidovirales, which accommodates viruses with the largest RNA genomes, includes the notorious coronaviruses; however, the evolutionary route for nidoviruses is not well understood. We have characterized a positive-sense (+) single-stranded (ss) RNA mycovirus, Rhizoctonia solani hypovirus 2 (RsHV2), from the phytopathogenic fungus Rhizoctonia solani. RsHV2 has the largest RNA genome size of 22,219 nucleotides, excluding the poly(A) tail, in all known mycoviruses, and contains two open reading frames (ORF1 and ORF2). ORF1 encodes a protein of 2,009 amino acid (aa) that includes a conserved helicase domain belonging to helicase superfamily I (SFI). In contrast, ORF2 encodes a polyprotein of 4459 aa containing the hallmark genes of hypoviruses. The latter includes a helicase belonging to SFII. Following phylogenetic analysis, the ORF1-encoded helicase (Hel1) unexpectedly clustered in an independent evolutionary branch together with nidovirus helicases, including coronaviruses, and bacteria helicases. Thus, Hel1 presence indicates the occurrence of horizontal gene transfer between viruses and bacteria. These findings also suggest that RsHV2 is most likely a recombinant arising between hypoviruses and nidoviruses.

中文翻译：

---

一种真菌病毒中的两个相距较远的解旋酶：真菌病毒、冠状病毒和其他巢状病毒之间水平基因转移的证据

Nidovirales 包含具有最大 RNA 基因组的病毒，包括臭名昭著的冠状病毒；然而，巢病毒的进化路线尚不清楚。我们鉴定了来自植物病原真菌立枯丝核菌的正链 (+) 单链 (ss) RNA 真菌病毒，立枯丝核菌低病毒 2 (RsHV2)。在所有已知的真菌病毒中，RsHV2 的 RNA 基因组大小最大，为 22,219 个核苷酸（不包括多聚腺苷酸尾），并包含两个开放阅读框（ORF1 和 ORF2）。ORF1 编码 2,009 个氨基酸 (aa) 的蛋白质，其中包含属于解旋酶超家族 I (SFI) 的保守解旋酶结构域。相比之下，ORF2编码含有低病毒标志基因的4459个氨基酸的多蛋白。后者包括属于 SFII 的解旋酶。经过系统发育分析，ORF1编码的解旋酶（Hel1）出乎意料地与巢状病毒解旋酶（包括冠状病毒和细菌解旋酶）一起聚集在一个独立的进化分支中。因此，Hel1 的存在表明病毒和细菌之间发生了水平基因转移。这些发现还表明，RsHV2 很可能是低病毒和巢病毒之间的重组体。