Constitutes the pattern-recognition receptor (PPR) that determines the specific perception of elongation factor Tu (EF-Tu), a potent elicitor of the defense response to pathogen-associated molecular patterns (PAMPs); phosphorylates BIK1 upon elicitation to regulate immune responses such as defense hormone expression (e.g. jasmonic acid (JA) and salicylic acid (SA)) (PubMed:29649442). Reduces transformation by Rhizobium radiobacter probably by inducing plant defense during the interaction. Binding to the effector AvrPto1 from P.syringae blocks the downstream plant immune response while interaction with hopD2 decreases the phosphorylation level of EFR upon elf18 treatment. Specific endoplasmic reticulum quality control components (ERD2B, CRT3, UGGT and STT3A) are required for the biogenesis of EFR. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Binds to Pseudomonas syringae AvrPto1 and (via the kinase and cytoplasmic domains) to hopD2. Interacts with SERK3/BAK1, SERK4/BKK1, SERK1 and SERK2 in a specific ligand-induced manner. Binds to IOS1 (PubMed:27317676). Binds to BIK1 in the absence of pathogen elicitor; dissociates upon pathogen-associated molecular pattern (PAMP)-triggered activation (PubMed:29649442). The last two LRR (561-597) are necessary for elf18 binding and functionality. Autophosphorylated after elicitation with elfl18. Autophosphorylation is inhibited by the binding with avrPto1. Phosphorylation at T-836 is required for immune signaling. Polyubiquitinated at the kinase domain mediated by P.syringae AvrPtoB. Enhanced susceptibility to R.radiobacter. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.