A Cysteine-Rich Receptor-Like Protein Kinase CaCKR5 Contributes to Immune Defense Against Ralstonia Solanacearum in Pepper

Abstract Background: Cysteine-rich receptor-like kinases (CRKs) represent a large subfamily of receptor-like kinases and have important roles in numerous different physiological processes in plants. Results: CaCRK5 transcripts were observed to accumulate after the inoculation of R. solanacearum and treatment with salicylic acid. The fusion between CaCRK5 and the green fluorescence protein was targeted to the plasma membrane. Suppression of CaCRK5 via virus-induced gene silencing made pepper plants significantly susceptible to R. solanacearum infection, which was accompanied by decreased expression of defense related genes CaPR1, CaSAR8.2, CaDEF1 and CaACO1. Overexpression of CaCRK5 in tobacco conferred increased resistance against R. solanacearum. Furthermore, electrophoretic mobility shift assay and chromatin immunoprecipitation with quantitative real-time PCR analysis verified that a homeodomain zipper I protein CaHDZ27 can bind to the CaCRK5 promoter, and directly active its expression. Yeast two-hybrid and bimolecular fluorescence complementation analyses suggested that CaCRK5 could heterodimerize with the homologous member CaCRK6 in the plasma membrane. Conclusions: Our data indicated that CaCRK5 played a positive role in pepper resistance against R. solanacearum infection.