Complete genome sequencing of cucumber mosaic virus from black pepper revealed rare deletion in the methyltransferase domain of 1a gene

Abstract

The complete genome of cucumber mosaic virus (CMV) from black pepper was sequenced and compared with CMV isolates from subgroups I and II reported worldwide. Percent identity and phylogenetic analyses clearly indicated that the CMV isolate from black pepper (BP) belongs to subgroup IB. Sequence analyses also showed the presence of a rare deletion of nine nucleotides in the putative methyltransferase domain of 1a gene which was observed only in two more isolates of CMV among one hundred 1a gene sequences of CMV for which sequence information is available in the database. Interestingly this deletion is not present in the black pepper isolate of CMV from China (WN1) and from Indian long pepper that is closely related to black pepper. Percent identity analyses showed that the 3’untranslated region (UTR) of the three RNAs of the BP isolate were conserved with 91% identity whereas the 5’UTR of three RNAs showed 52-80% identity. The level of gene conservation among the subgroups was highest in coat protein and lowest in 2b. The values of nucleotide diversity studies were further consistent with the above data. The ratio of non-synonymous to the synonymous substitution of the five genes of three RNAs was in the order 1a>2a>2b>3a>3b and less than one for all the genes, indicating purifying selection. These clearly reflect that the protein encoded by RNA1 is highly tolerant to amino acid changes followed by that of RNA2 and, RNA3 is the least tolerant correlating to its functional importance.