A novel non-segmented double-stranded RNA virus from an Arctic isolate of Pythium polare.

We investigated virus infection in the oomycete Pythium polare from the Arctic. From 39 isolates investigated, 14 contained virus-like double-stranded RNA (dsRNA). Next generation sequencing revealed that the P. polare isolate OPU1176 contained three different virus-like sequences. We determined the full-length genome sequence of one of them. The 5397 nt-length genome had two overlapped open reading frames (ORFs) consistent with a toti and toti-like viruses, that we named Pythium polare RNA virus 1 (PpRV1). The ORF2 encoded an RNA-dependent RNA polymerase (RdRp). The shifty heptamer motif and RNA pseudoknot were predicted near the stop codon of ORF1, implying that the RdRp could be translated as a fusion protein with the ORF1 protein. Phylogenetic analysis with deduced RdRp amino acid sequences indicated that oomycete virus PpRV1 was closely related to the unclassified arthropod toti-like viruses. The comparison of PpRV1-free and -infected lines suggested that PpRV1 infected in a symptomless manner.