NtRNF217, Encoding a Putative RBR E3 Ligase Protein of Nicotiana tabacum, Plays an Important Role in the Regulation of Resistance to Ralstonia solanacearum Infection.

E3 ubiquitin ligases, the most important part of the ubiquitination process, participate in various processes of plant immune response. RBR E3 ligase is one of the E3 family members, but its functions in plant immunity are still little known. NtRNF217 is a RBR E3 ligase in tobacco based on the sequence analysis. To assess roles of NtRNF217 in tobacco responding to Ralstonia solanacearum, overexpression experiments in Nicotiana tabacum (Yunyan 87, a susceptible cultivar) were performed. The results illuminated that NtRNF217-overexpressed tobacco significantly reduced multiplication of R. solanacearum and inhibited the development of disease symptoms compared with wild-type plants. The accumulation of H2O2 and O2- in NtRNF217-OE plants was significantly higher than that in WT-Yunyan87 plants after pathogen inoculation. The activities of CAT and SOD also increased rapidly in a short time after R. solanacearum inoculation in NtRNF217-OE plants. What is more, overexpression of NtRNF217 enhanced the transcript levels of defense-related marker genes, such as NtEFE26, NtACC Oxidase, NtHIN1, NtHSR201, and NtSOD1 in NtRNF217-OE plants after R. solanacearum inoculation. The results suggested that NtRNF217 played an important role in regulating the expression of defense-related genes and the antioxidant enzymes, which resulted in resistance to R. solanacearum infection.