Structure-function study of LYR3: a LysM-RLK which binds lipo-chitooligosaccharides with high affinity.

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Malkov, Nikita | Fliegmann, Judith | Rosenberg, Charles | Gasciolli, Virginie | Timmers, Ton | Cullimore, Julie Vera | Bono, Jean-Jacques

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International audience. In Medicago truncatula the lysin motif receptor-like kinase (LysM-RLK), LYR3, has been identified as a high affinity binding protein for lipo-chitooligosaccharides (LCOs), i.e. the symbiotic signals that include the Nod factors and the Myc-LCOs. MtLYR3 produced in a heterologous system, Nicotiana benthamiana leaves, has an affinity for LCOs in the nM range and shows over a 100-fold specificity for LCOs vs COs (chitooligosaccharides), (Fliegmann et al., 2013, ACS Chem Biol 8, 1900-1906). In this work, LYR3 has been cloned and characterized from other legume species and its specificity has been determined for Nod factors derived from Rhizobial symbionts and for Myc-LCOs from arbuscular mycorrhizal fungi. All the LYR3 orthologs exhibited binding characteristics similar to that of MtLYR3, except for the one from Lupinus angustifolius where LCO binding could not be detected. In order to determine the regions in the extracellular domain which are required for high affinity LCO binding, domain swapping between M. truncatula and L. angustifolius LYR3 proteins was carried out. By this approach, the crucial role of the third lysin motif in LCO binding has been demonstrated, suggesting that LCO recognition by LYR3 might differ from that of CO by OsCEBiP or AtCERK1 for which the ligand binding relies primarily on the second lysin motif.

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