A look at plant immunity through the window of the multitasking coreceptor BAK1

- BAK1 acts as a shared coreceptor for LRR-RLKs/RLPs in pattern recognition.
- Use of bak1-5 hypoactive allele facilitates to reveal PRR-related BAK1 function.
- PRR- and NLR-related mechanisms activate immunity following BAK1/SERK4 depletion.
- BAK1 depletion is not favored by host plants and pathogens as a means to attenuate PTI.
- PRR complexes may access and phosphorylate PTI regulators on scaffold proteins.

Recognition of microbe- and danger-associated molecular patterns (MAMPs and DAMPs, respectively) by pattern recognition receptors (PRRs) is central to innate immunity in both plants and animals. The plant PRRs described to date are all cell surface-localized receptors. According to their ligand-binding ectodomains, each PRR engages a specific coreceptor or adaptor kinase in its signaling complexes to regulate defense signaling. With a focus on the coreceptor RLK BRI1-ASSOCIATED RECEPTOR KINASE1 (BAK1) and related SOMATIC EMBRYOGENESIS RECEPTOR KINASEs (SERKs), here we review the increasing inventory of BAK1 partners and their functions in plant immunity. We also discuss the significance of autoimmunity triggered by BAK1/SERK4 disintegration in shaping the strategies for attenuation of PRR signaling by infectious microbes and host plants.