Molecular characterization of Potato mop-top virus isolates from China and Canada and development of RT-PCR differentiation of two sequence variant groups

AbstractThe complete genome comprising three genomic RNAs of three Canadian and two Chinese isolates of Potato mop-top virus were sequenced and analysed. Two open reading frames (ORFs) were found in RNA1 of 6.1 kb, encoding a readthrough RNA-dependent RNA polymerase (RdRp). A coat protein (CP)-readthrough protein was encoded by RNA2 of 3.1 kb. Four ORFs that encoded the triple gene block proteins (TGBps) and a cysteine-rich protein were found in RNA3 (2.9 kb) of the Chinese isolate ‘Yunnan’; whereas in the remaining isolates (three Canadian isolates and the Chinese isolate ‘Guangdong’), only three ORFs encoding TGBps were observed in RNA3. A single nucleotide mutation of A2462 to G2462 abolished the start codon ‘AUG’ for the fourth putative ORF in RNA3 of these isolates. Based on phylogenetic and sequence similarity analysis of these isolates as well as those reported by others at the complete RNA sequence level, each of RNA1, RNA2 and RNA3 could be divided into at least two groups. In Canadian isolates ‘...