LYR 3, a high‐affinity LCO ‐binding protein of Medicago truncatula , interacts with LYK 3, a key symbiotic receptor

LYR3, LYK 3, and NFP are lysin motif‐containing receptor‐like kinases (LysM‐ RLK s) from Medicago truncatula, involved in perception of symbiotic lipo‐chitooligosaccharide ( LCO ) signals. Here, we show that LYR 3, a high‐affinity LCO ‐binding protein, physically interacts with LYK 3, a key player regulating symbiotic interactions. In vitro , LYR 3 is phosphorylated by the active kinase domain of LYK 3. Fluorescence lifetime imaging/Förster resonance energy transfer ( FLIM / FRET ) experiments in tobacco protoplasts show that the interaction between LYR 3 and LYK 3 at the plasma membrane is disrupted or inhibited by addition of LCO s. Moreover, LYR 3 attenuates the cell death response, provoked by coexpression of NFP and LYK 3 in tobacco leaves.