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Curr Biol. 2014 Jan 20;24(2):134-43. doi: 10.1016/j.cub.2013.11.047. Epub 2014 Jan 2.

The leucine-rich repeat receptor kinase BIR2 is a negative regulator of BAK1 in plant immunity.

Author information

1
Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
2
Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ 85721, USA.
3
Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany; The Sainsbury Laboratory, Norwich Research Park, Norwich NR4 7UH, UK.
4
Analytics (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
5
Zurich-Basel Plant Science Center, Department of Environmental Sciences, University of Basel, 4056 Basel, Switzerland.
6
Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609, USA.
7
The Sainsbury Laboratory, Norwich Research Park, Norwich NR4 7UH, UK.
8
Laboratory of Biochemistry, Wageningen University, Wageningen 6703 HA, the Netherlands.
9
Department of Plant Biochemistry (ZMBP), Eberhard Karls University Tübingen, 72076 Tübingen, Germany. Electronic address: birgit.kemmerling@zmbp.uni-tuebingen.de.

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.

PMID:
24388849
DOI:
10.1016/j.cub.2013.11.047
[Indexed for MEDLINE]
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