Thierry Halter1, Julia Imkampe1, Sara Mazzotta1, Michael Wierzba2, Sandra Postel1, Christoph Bücherl3, Christian Kiefer1, Mark Stahl4, Delphine Chinchilla5, Xiaofeng Wang6, Thorsten Nürnberger1, Cyril Zipfel7, Steven Clouse6, Jan Willem Borst8, Sjef Boeren8, Sacco C de Vries8, Frans Tax2, Birgit Kemmerling9. 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.
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: Irene Guzmán-Benito; Livia Donaire; Vítor Amorim-Silva; José G Vallarino; Alicia Esteban; Andrzej T Wierzbicki; Virginia Ruiz-Ferrer; César Llave Journal: New Phytol Date: 2019-06-28 Impact factor: 10.151