title: Cleavage of the SYMBIOSIS RECEPTOR-LIKE KINASE ectodomain promotes complex formation with Nod factor receptor 5.
abstract: Plants form root symbioses with fungi and bacteria to improve their nutrient supply. SYMBIOSIS RECEPTOR-LIKE KINASE (SYMRK) is required for phosphate-acquiring arbuscular mycorrhiza, as well as for the nitrogen-fixing root nodule symbiosis of legumes and actinorhizal plants, but its precise function was completely unclear. Here we show that the extracytoplasmic region of SYMRK, which comprises three leucine-rich repeats (LRRs) and a malectin-like domain (MLD) related to a carbohydrate-binding protein from Xenopus laevis, is cleaved to release the MLD in the absence of symbiotic stimulation. A conserved sequence motif--GDPC--that connects the MLD to the LRRs is required for MLD release. We discovered that Nod factor receptor 5 (NFR5) forms a complex with the SYMRK version that remains after MLD release (SYMRK-ΔMLD). SYMRK-ΔMLD outcompeted full-length SYMRK for NFR5 interaction, indicating that the MLD negatively interferes with complex formation. SYMRK-ΔMLD is present at lower amounts than MLD, suggesting rapid degradation after MLD release. A deletion of the entire extracytoplasmic region increased protein abundance, suggesting that the LRR region promotes degradation. Curiously, this deletion led to excessive infection thread formation, highlighting the importance of fine-tuned regulation of SYMRK by its ectodomain.
authors: Genetics, Faculty of Biology, University of Munich (LMU), Großhaderner Straße 4, 82152 Martinsried, Germany.
authors: Meritxell
authors: M
authors: Antolín-Llovera
authors: Genetics, Faculty of Biology, University of Munich (LMU), Großhaderner Straße 4, 82152 Martinsried, Germany.
authors: Martina K
authors: MK
authors: Ried
authors: Genetics, Faculty of Biology, University of Munich (LMU), Großhaderner Straße 4, 82152 Martinsried, Germany. Electronic address: parniske@lmu.de.
authors: Martin
authors: M
authors: Parniske
mesh_terms: D005110:Extracellular Space / Q000378:metabolism; D000070116:Lotus / Q000201:enzymology* / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D011485:Protein Binding; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D013559:Symbiosis
chemical_list: D010940:Plant Proteins; D011494:Protein Kinases