TAXONOMIC RELATIONSHIPS BETWEEN DISTINCT POTATO VIRUS-Y ISOLATES BASED ON DETAILED COMPARISONS OF THE VIRAL COAT PROTEINS AND 3'-NONTRANSLATED REGIONS

Detailed comparisons were made of the sequences of the coat protein (C P) cistrons and 3'-nontranslated regions (3'-NTR) of 21 (geographicall y) distinct isolates of potato virus Y (PVY) and a virus isolate initi ally described as pepper mottle virus (PepMoV). Multiple sequence alig nments and phylogenetic relationships based on these alignments result ed into a subgrouping of virus isolates which largely corresponded wit h the historical strain differentiation based on biological criteria a s host range, symptomatology and serology. Virus isolates belonging to the same subgroup shared a number of characteristic CP amino acid and 3'-NTR nucleotide residues indicating that, by using sequences from t he 3'-terminal region of the potyvirus genome, a distinction could be made between different isolates of one virus species as well as betwee n different virus species. RNA secondary structure analysis of the 3'- NTR of twelve PVY isolates revealed four major stem-loop structures of which, surprisingly, the loop sequences gave a similar clustering of isolates as resulting from the overall comparisons of CP and 3'-NTR se quences. This implies a biological significance of these structural el ements.