A double-stranded RNA from a Phytophthora species is related to the plant endornaviruses and contains a putative UDP glycosyltransferase gene

Abstract

A new dsRNA was isolated from a Phytophthora isolate from Douglas fir. Sequence analysis showed the dsRNA to consist of 13 883 bp and to contain a single open reading frame with the potential to encode a polyprotein of 4548 aa. This polyprotein contained amino acid sequence motifs characteristic of virus RNA-dependent RNA polymerases (RdRps) in its C-terminal region and motifs characteristic of RNA helicases in its N-terminal region. These sequence motifs were related to corresponding motifs in plant viruses in the genus Endornavirus. In phylogenetic trees constructed from the RdRp and helicase motifs of a range of ssRNA and dsRNA viruses, the Phytophthora RdRp and helicase sequences clustered with those of the plant endornaviruses with good bootstrap support. The properties of the Phytophthora dsRNA are consistent with its being classified as the first non-plant member of the genus Endornavirus, for which we propose the name phytophthora endornavirus 1 (PEV1). A region between the RdRp and helicase domains of the PEV1 protein had significant amino acid sequence similarity to UDP glycosyltransferases (UGTs). Two sequence motifs were identified, one characteristic of all UGTs and the other characteristic of sterol UGTs. The PEV1 UGT would be the first for an RNA virus, although ecdysteroid UGT genes have been found in many baculoviruses. The PEV1 UGT was only distantly related to baculovirus ecdysteroid UGTs, which belong to a family distinct from the sterol UGTs.