Resistance against Ralstonia solanacearum in tomato depends on the methionine cycle and the γ-aminobutyric acid metabolic pathway.

Bacterial wilt caused by Ralstonia solanacearum is a complex and destructive disease that affects over 200 plant species. To investigate the interaction of R. solanacearum and its tomato (Solanum lycopersicum) plant host, a comparative proteomic analysis was conducted in tomato stems inoculated with highly and mildly aggressive R. solanacearum isolates (RsH and RsM, respectively). The results indicated a significant alteration of the methionine cycle (MTC) and downregulation of γ-aminobutyric acid (GABA) biosynthesis. Furthermore, transcriptome profiling of two key tissues (stem and root) at three stages (0, 3 and 5 days post-inoculation) with RsH in resistant and susceptible tomato plants is presented. Transcript profiles of MTC and GABA pathways were analyzed. Subsequently, the MTC-associated genes SAMS2, SAHH1 and MS1 and the GABA biosynthesis-related genes GAD2 and SSADH1 were knocked-down by virus-induced gene silencing and the plants' defense responses upon infection with R. solanacearum RsM and RsH were analyzed. These results showed that silencing of SAHH1, MS1 and GAD2 in tomato leads to decreased resistance against R. solanacearum. In summary, the infection assays, proteomic and transcriptomic data described in this study indicate that both MTC and GABA biosynthesis play an important role in pathogenic interaction between R. solanacearum and tomato plants.