Enhancement of the expression of defense genes in tomato against Ralstonia solanacearum by N-octanoyl-L-homoserine lactone

Many Gram-negative bacteria use N-acyl-homoserine lactone (AHLs) as quorum sensing (QS) signalling molecules to monitor their population density and to regulate gene expression in a density dependent manner. Recently, it has been shown that AHLs are detected by the plants and they trigger plant defense responses. In this study, N-octanoyl-L-homoserine lactone (C8-HSL) has been used as resistant inducer against bacterial wilt disease of tomato caused by Ralstonia solanacearum. The present investigation focused on the role of defense related enzymes (phenylalanine ammonia lyase, peroxidase, polyphenol oxidase and lipoxygenase) in imparting resistance in tomato against R. solanacearum. Activities of these defense enzymes, increased in C8-HSL treated tomato plants, which were challenged with R. solanacearum. The transcripts accumulation studies for these enzymes were carried out using semi-quantitative reverse transcription PCR, with maximum mRNA accumulation in resistant cultivar upon treatment with C8-HSL. Quantitative real time-PCR (qRT-PCR) confirmed the maximum induction of all these four genes in C8-HSL treated plants. However, the expression of defense genes was higher in C8-HSL treated resistant cultivar than that of susceptible cultivar. Therefore, the results support the view that C8-HSL molecule enhances disease protection against R. solanacearum infection in tomato through the activation of defense genes.