Symbiosis or defense: the molecular mechanism involving LysM receptors of the model legume Lotus japonicus
S. RADUTOIU (1), J. Cheng (1), M. Blaise (2), J. Stougaard (1), Z. Bozsoki (1) (1) Aarhus University/CARB, Denmark; (2) CNRS, Centre d’études d’agents Pathogènes et Biotechnologies pour la Santé, Université de Montpellier, France

Chitin oligomers derived from fungal cell walls are recognized as PAMPSs and elicit defense responses in plants. On the other hand symbiotic nitrogen fixing rhizobia bacteria produce signaling molecules with a chitin backbone that are essential for the symbiosis initiation (Nod factors). LysM motif containing receptors have been shown previously to be essential for perception of chitin-backbone-containing molecules. Rice CEBiP and Arabidopsis CERK1 are indispensable for chitin elicited defense signaling, while legumes mutated in L. japonicus NFR1 and NFR5 are unable to respond to Nod factors and symbiotic bacteria. We have identified and characterized the chitin receptor in L. japonicus, LYS6. lys6 mutant plants fail to respond to chitin oligomers with oxidative burst, MAPK3/6 phosphorylation or defense gene activation, but are still able to form efficient symbiosis with rhizobia and arbuscular mycorrhiza. On the other hand, nfr1 mutants respond normally to chitin oligomers. NFR1 and LYS6 share 78% similarity in their amino acid sequences, are expressed in the same type of root cells, yet drive signaling pathways leading to opposing outcomes. We aim to identify molecular patterns present in the two receptors responsible for the symbiosis/defense decision at the very first steps of microbe recognition to broaden our understanding on the function and evolution of LysM receptor-mediated signaling in root cells. For this we use single and double mutant phenotypic analyses coupled with genetic complementation studies using synthetic receptor molecules. The results of our analyses will be presented and discussed.

Abstract Number: P1-8
Session Type: Poster