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Abstract：
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.
摘要：
Nidovirales,容纳具有最大RNA基因组的病毒，包括臭名昭著的冠状病毒；然而，目前还没有很好地理解nidovirus的进化途径。我们已经表征了一个阳性（+）单链（ss）RNA分枝杆菌病毒，枯丝核菌2型病毒（RsHV2），来自植物病原真菌枯萎病。RsHV2具有最大的RNA基因组大小，为22,219个核苷酸，不包括聚(A)尾部，在所有已知的分枝杆菌病毒中，并且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,其包括属于解旋酶超家族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4459aa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）与nidovirus解旋酶意外地聚集在一个独立的进化分支中，包括冠状病毒,和细菌解旋酶。因此，Hel1的存在表明病毒和细菌之间发生水平基因转移。这些发现还表明RsHV2很可能是在低病毒和中性病毒之间产生的重组体。
