Isolation, characterization and evolution of NBS-LRR encoding disease-resistance gene analogs in eggplant against bacterial wilt

Bacterial wilt (causal organism-Ralstonia solanacearum) is one of the most important soil-borne diseases of eggplant (Solanum melongena) worldwide. The best way to control it economically is to develop cultivars resistant to this soil-borne pathogen. Resistance gene (R-gene) cloning and sequencing to obtain resistance gene analogs (RGAs) is one of the most recent approaches for obtaining disease resistant cultivars. Three different types of degenerative PCR based primers were used for isolating RGAs from resistant cultivated/wild species through amplification of the target region of nucleotide binding site-leucine rich repeat (NBS-LRR). Genetic diversity was observed in the sequences isolated, and six sequences showing specific conserved motifs were shortlisted as Solanum melongena RGAs (Sm7RGA1, Sm7RGA2, Sm7RGA4, Sm7RGA8 and Sm7RGA10) and Solanum viarum RGA (SvRGA2). The RGAs isolated in this study belong to both toll interleukin-1 receptors (TIR)-NBS-LRR and non-TIR-NBS-LRR type R-genes and show similarity with other plant resistance genes. This study also confirmed the hypothesis that dicots have both TIR and non-TIR resistance genes. The present study on eggplant RGAs will help develop RGA based markers linked to bacterial wilt in eggplant and other plant species. Further, it will provide information and pave the way for elucidation at the molecular level of wild and cultivated species’ mechanism of resistance to bacterial wilt. This is the first report of NBS-LRR class resistance genes/RGA in resistant eggplant and its wild relatives against bacterial wilt (BW).