An EFR-Cf-9 chimera confers enhanced resistance to bacterial pathogens by SOBIR1- and BAK1-dependent recognition of elf18

The transfer of well-studied native and chimeric pattern recognition receptors (PRRs) to susceptible plants are strategies to improve host resistance. In most cases, the ectodomain determines PRR recognition specificity, while the endodomain determines output quality and intensity. Here we report the generation and characterization of a chimeric receptor, carrying the ectodomain of the Arabidopsis thaliana EF-Tu receptor (EFR), and the endodomain of the tomato Cf-9 resistance protein. The chimera was expressed both transiently and stably in tobacco, and triggered a robust hypersensitive response upon elf18 treatment. Co-immunoprecipitation and virus-induced gene silencing studies showed that the chimera constitutively interacts with the SUPPRESSOR OF BIR1-1 (SOBIR1) co-receptor, and requires both SOBIR1 and kinase-active BRI1-ASSOCIATED KINASE-1 (BAK1) for its function. Transgenic plants expressing EFR-Cf-9 were more resistant to the hemibiotrophic bacterial pathogen Pseudomonas amygdali pv tabaci, indicating that this chimeric receptor is a valuable tool for both investigating the molecular mechanisms responsible for the activation of defense response by PRRs and R proteins, and for biotechnological use to improve crop disease resistance.