title: A flagellin-induced complex of the receptor FLS2 and BAK1 initiates plant defence.
abstract: Plants sense potential microbial invaders by using pattern-recognition receptors to recognize pathogen-associated molecular patterns (PAMPs). In Arabidopsis thaliana, the leucine-rich repeat receptor kinases flagellin-sensitive 2 (FLS2) (ref. 2) and elongation factor Tu receptor (EFR) (ref. 3) act as pattern-recognition receptors for the bacterial PAMPs flagellin and elongation factor Tu (EF-Tu) (ref. 5) and contribute to resistance against bacterial pathogens. Little is known about the molecular mechanisms that link receptor activation to intracellular signal transduction. Here we show that BAK1 (BRI1-associated receptor kinase 1), a leucine-rich repeat receptor-like kinase that has been reported to regulate the brassinosteroid receptor BRI1 (refs 6,7), is involved in signalling by FLS2 and EFR. Plants carrying bak1 mutations show normal flagellin binding but abnormal early and late flagellin-triggered responses, indicating that BAK1 acts as a positive regulator in signalling. The bak1-mutant plants also show a reduction in early, but not late, EF-Tu-triggered responses. The decrease in responses to PAMPs is not due to reduced sensitivity to brassinosteroids. We provide evidence that FLS2 and BAK1 form a complex in vivo, in a specific ligand-dependent manner, within the first minutes of stimulation with flagellin. Thus, BAK1 is not only associated with developmental regulation through the plant hormone receptor BRI1 (refs 6,7), but also has a functional role in PRR-dependent signalling, which initiates innate immunity.
authors.affiliation: Zurich-Basel Plant Science Center, Botanical Institute, University of Basel, Hebelstrasse 1, 4056 Basel, Switzerland. delphine.chinchilla@unibas.ch
authors.forename: Delphine
authors.initials: D
authors.lastname: Chinchilla
authors.forename: Cyril
authors.initials: C
authors.lastname: Zipfel
authors.forename: Silke
authors.initials: S
authors.lastname: Robatzek
authors.forename: Birgit
authors.initials: B
authors.lastname: Kemmerling
authors.forename: Thorsten
authors.initials: T
authors.lastname: Nürnberger
authors.forename: Jonathan D G
authors.initials: JD
authors.lastname: Jones
authors.forename: Georg
authors.initials: G
authors.lastname: Felix
authors.forename: Thomas
authors.initials: T
authors.lastname: Boller
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000276:immunology* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D001665:Binding Sites; D005408:Flagellin / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D008024:Ligands; D009154:Mutation / Q000235:genetics; D010444:Peptide Elongation Factor Tu / Q000378:metabolism; D010935:Plant Diseases / Q000276:immunology*; D011485:Protein Binding; D011494:Protein Kinases / Q000276:immunology / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D008024:Ligands; D005408:Flagellin; D011494:Protein Kinases; C463660:BAK1 protein, Arabidopsis; C411853:FLS2 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; D010444:Peptide Elongation Factor Tu