Phylogenetic analysis and homologies of the replicase of tomato leaf curl geminiviruses: implications for obtaining pathogen derived resistance.

Geminiviruses encode a replication initiator protein, Rep, which binds to iterated DNA motifs functioning as essential elements for virus specific replication. Rep protein gene of three isolates of whitefly transmitted geminivirus causing leaf curl disease of tomato in India were amplified, cloned and sequenced. Nucleotide sequence and the derived amino acid sequence for the replicase gene of these isolates was determined and included in an analysis with the published sequences. Phylogenetic relationship clearly indicates two subsets, one belonging to Tomato leaf curl virus (ToLCV) having bipartite genome and the other having the monopartite genome. Comparisons of various functional domains and motifs involved in specificity determinants, DNA-binding and catalysis were discussed. The implications of the sequence analysis were discussed with respect to the strategy for the generation of engineered resistance having wide spectrum applications.