BAK1 and BKK1 are required for innate immunity to hemibiotrophic and biotrophic pathogens

Some proteins from the SERK family, BAK1/SERK3 and BKK1/SERK4, are known for interact with BRI1 and be positive regulators of the BR signaling pathway. In other hand, PRRs are transmembrane pattern recognition receptors that are critical for antibacterial immunity, where FLS2 (whose ligand is flg22) and EFR (who binds elf18) are the best studied receptors in A.thaliana. In this work, the authors demonstrated in different plant systems that FLS2 and EFR receptors interact with several SERKs in a ligand-induced manner. This group also identified a new bak1 mutant, bak1-5, that possesses a reduce phosphorylation status, which not affects BR responses, but elf18 and flg22 ligand responses. MPK activation and induction of expression of PAMP-induced marker genes is affected in bak1-5 and bkk1-1 singles and bak1-5 bkk1-1 double mutants, which evidences that both BAK1 and BKK1 contribute for EFR and FLS2 response. Furthermore, after testing different biotrophic pathogens, BAK1 and BKK1 shown to be required also for resistance to P.syringae and H.arabidopsidis (hemibiotrophic and obligate biotrophic pathogens respectively).