Nod factor perception and signal transduction during endosymbiotic interactions of Medicago truncatula.

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Timmers, Ton | Fliegmann, Judith | Malkov, Nikita | Cullimore, Julie Vera | Bono, Jean-Jacques

Edité par CCSD -

International audience. The legume Medicago truncatula maintains endosymbiotic interactions under phosphate and nitrate limiting conditions with respectively mycorrhizal fungi and rhizobia. Both microsymbionts produce lipochitooligosaccharides (LCOs) which are perceived by plant receptors with extracellular LysM domains and an intracellular kinase domain (LysMRLKs). Mycorrhizal fungi in addition secrete short chain chitooligosaccharides (COs) those function as signal molecules. Three LysMRLKs from M. truncatula, LYR3, LYK3 and NFP, were studied in detail in our group. LYR3 is a high affinity binding protein for LCOs but not for COs. Swapping experiments with LysM domains from different plant species identified the crucial role of the third LysM motif in LCO binding. LYR3 from two Lupinus species which do not form mycorrhizal symbiosis are deficient in high affinity binding to LCOs. LYR3 and NFP lack an active kinase domain and LYR3 is phosphorylated by the active kinase domain of LYK3. FRET experiments showed that LYR3 and LYK3 interact at the plasmamembrane and this interaction is inhibited by addition of LCOs. Co-expression of NFP and LYK3 in tobacco leaves provokes a cell death response that is attenuated in the presence of LYR3. Low level expression of these 3 proteins hampers their localization in roots of M. truncatula and ongoing experiments to increase the detection sensitivity and thus study the distribution of these proteins during endosymbiotic interactions will be presented.

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