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Identification of a High Affinity Binding Site for Lipo-oligosaccharidic NodRm Factors in the Microsomal Fraction of Medicago Cell Suspension Cultures

¹Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, UMR 215 INRA-CNRS, BP 27, 31326 Castanet-Tolosan Cédex, France; ²Signaux et Messages Cellulaires chez les Végétaux, UMR 5546, CNRS-Université Paul Sabatier, 118 Route de Narbonne, 31162 Toulouse Cédex, France

Protease-sensitive binding sites for a ³⁵S-labeled ligand corresponding to the major lipo-oligosaccharidic symbiotic signal of Rhizobium meliloti (NodRm factor), have been identified in the microsomal fraction of Medicago varia cell suspension culture extracts. Binding was reversible and saturable and tetra-N-acetyl chitotetraose was a poor competitor of NodRm binding. Scatchard analysis suggests the presence of a high affinity binding site, termed Nod factor binding site two (NFBS2), with a K_d of 1.9 nM, and perhaps a second site with an affinity (K_d of 70 nM) similar to that of a site (NFBS1) previously characterized in Medicago truncatula root extracts.

Additional keywords: receptors, symbiosis.