title: The leucine-rich repeat receptor kinase BIR2 is a negative regulator of BAK1 in plant immunity.
abstract: BACKGROUND
  Transmembrane leucine-rich repeat (LRR) receptors are commonly used innate immune receptors in plants and animals but can also sense endogenous signals to regulate development. BAK1 is a plant LRR-receptor-like kinase (RLK) that interacts with several ligand-binding LRR-RLKs to positively regulate their functions. BAK1 is involved in brassinosteroid-dependent growth and development, innate immunity, and cell-death control by interacting with the brassinosteroid receptor BRI1, immune receptors, such as FLS2 and EFR, and the small receptor kinase BIR1, respectively.
  
  
  RESULTS
  Identification of in vivo BAK1 complex partners by LC/ESI-MS/MS uncovered two novel BAK1-interacting RLKs, BIR2 and BIR3. Phosphorylation studies revealed that BIR2 is unidirectionally phosphorylated by BAK1 and that the interaction between BAK1 and BIR2 is kinase-activity dependent. Functional analyses of bir2 mutants show differential impact on BAK1-regulated processes, such as hyperresponsiveness to pathogen-associated molecular patterns (PAMP), enhanced cell death, and resistance to bacterial pathogens, but have no effect on brassinosteroid-regulated growth. BIR2 interacts constitutively with BAK1, thereby preventing interaction with the ligand-binding LRR-RLK FLS2. PAMP perception leads to BIR2 release from the BAK1 complex and enables the recruitment of BAK1 into the FLS2 complex.
  
  
  CONCLUSIONS
  Our results provide evidence for a new regulatory mechanism for innate immune receptors with BIR2 acting as a negative regulator of PAMP-triggered immunity by limiting BAK1-receptor complex formation in the absence of ligands.
authors.affiliation: Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
authors.forename: Thierry
authors.initials: T
authors.lastname: Halter
authors.affiliation: Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Imkampe
authors.affiliation: Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
authors.forename: Sara
authors.initials: S
authors.lastname: Mazzotta
authors.affiliation: Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Wierzba
authors.affiliation: Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Postel
authors.affiliation: Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany; The Sainsbury Laboratory, Norwich Research Park, Norwich NR4 7UH, UK.
authors.forename: Christoph
authors.initials: C
authors.lastname: Bücherl
authors.affiliation: Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Kiefer
authors.affiliation: Analytics (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Stahl
authors.affiliation: Zurich-Basel Plant Science Center, Department of Environmental Sciences, University of Basel, 4056 Basel, Switzerland.
authors.forename: Delphine
authors.initials: D
authors.lastname: Chinchilla
authors.affiliation: Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609, USA.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Nürnberger
authors.affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich NR4 7UH, UK.
authors.forename: Cyril
authors.initials: C
authors.lastname: Zipfel
authors.affiliation: Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609, USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Clouse
authors.affiliation: Laboratory of Biochemistry, Wageningen University, Wageningen 6703 HA, the Netherlands.
authors.forename: Jan Willem
authors.initials: JW
authors.lastname: Borst
authors.affiliation: Laboratory of Biochemistry, Wageningen University, Wageningen 6703 HA, the Netherlands.
authors.forename: Sjef
authors.initials: S
authors.lastname: Boeren
authors.affiliation: Laboratory of Biochemistry, Wageningen University, Wageningen 6703 HA, the Netherlands.
authors.forename: Sacco C
authors.initials: SC
authors.lastname: de Vries
authors.affiliation: Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Frans
authors.initials: F
authors.lastname: Tax
authors.affiliation: Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany. Electronic address: birgit.kemmerling@zmbp.uni-tuebingen.de.
authors.forename: Birgit
authors.initials: B
authors.lastname: Kemmerling
mesh_terms: D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D016923:Cell Death; D018506:Gene Expression Regulation, Plant; D008024:Ligands; D009154:Mutation; D010766:Phosphorylation; D057865:Plant Immunity; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*
chemical_list: D029681:Arabidopsis Proteins; D008024:Ligands; C000591021:BIR2 protein, Arabidopsis; D011494:Protein Kinases; C463660:BAK1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases