Complete genome sequence of a divergent sweet potato chlorotic stunt virus isolate infecting Calystegia hederacea in China.

Sweet potato chlorotic stunt virus (SPCSV; genus Crinivirus, family Closteroviridae) is one of the most destructive viruses infecting sweet potatoes. In this study, we determined the complete genome sequence of an SPCSV-like isolate (CH) from Calystegia hederacea Wall. (Convolvulaceae), a weed species related to sweet potato, by combining next-generation sequencing and rapid amplification of cDNA ends. Comparisons of genome sequences and organization confirmed the classification of CH as SPCSV. However, the sequences and phylogenetic data revealed substantial genetic divergence between CH and all known SPCSV isolates. The amino acid sequence identity between the putative proteins in SPCSV-CH and the corresponding proteins in other known SPCSV isolates in each case was less than 85.0%. Phylogenetic analysis indicated that SPCSV-CH is separate from the groups of the known SPCSV isolates. Additionally, SPCSV-CH RNA1 lacks a p22 gene. A 10.1-kDa putative protein (p10) encoded by a sequence in the 5'-terminal region of RNA2 in SPCSV-CH is much larger than the corresponding protein in all known SPCSV isolates.