Nucleotide sequence analysis of Plum pox virus isolate W3174: evidence of a new strain.

The nucleotide sequence of Plum pox virus (PPV) isolate W3174 was determined. The virus genome consists of 9788 nucleotides (nt), excluding the poly(A) tail at the 3'-terminus, with 5'- and 3'-untranslated regions (UTRs) of 146 and 219 nt, respectively. The deduced polyprotein consists of 3141 amino acid (aa) residues, with the coat protein region consisting of 993 nt (331 aa). In comparisons with PPV-D, -M, -EA and -C isolates, nucleotide identity levels ranged from 79 to 80% for the entire genome and from 78 to 79%, 78 to 81%, and 92 to 95% for the NIb, CP, and 3'-UTR regions, respectively. The majority of nucleotide substitutions in the NIb region of W3174 are silent, while substitutions in the CP region are not silent, giving aa identities of 89-91% and 79-81%, respectively. The HC-Pro region contains the KITC and PTK motifs, and the DAG motif is located at positions 12-14 of the deduced CP aa sequence, all associated with aphid transmission. Phylogenetic analysis based on the complete genome sequence, the NIb, CP, and 3'-UTR region were performed. PPV-W3174 consistently formed a distinct clade or group, when compared to members of all four recognized strains of PPV, indicating that it is genetically distinct. These results are consistent with serological and nucleic acid-based strain typing data and justify recognition of this isolate as representative of a new strain identified as PPV-W.