title: Lipo-chitooligosaccharide Nodulation Signals from Rhizobium meliloti Induce Their Rapid Degradation by the Host Plant Alfalfa.
abstract: Extracellular enzymes from alfalfa (Medicago sativa L.) involved in the degradation of nodulation (Nod) factors could be distinguished by their different cleavage specificities and were separated by lectin affinity chromatography. A particular glycoprotein was able to release an acylated lipo-disaccharide from all tested Nod factors having an oligosaccharide chain length of four or five residues. Structural modifications of the basic lipo-chitooligosaccharide did not affect the cleavage site and had only weak influence on the cleavage efficiency of Nod factors tested. The acylated lipo-trisaccharide was resistant to degradation. When alfalfa roots were preincubated with Nod factors at nanomolar concentrations, the activity of the dimer-forming enzyme was stimulated up to 6-fold within a few hours. The inducing activity of Nod factors decreased in the order NodRm-IV(C16:2,Ac,S) > NodRm-IV(C16:2,S) and NodRm-V(C16:2,Ac,S) > NodRm-V(C16:2,S) > NodRm-IV(C16:0,S) > NodRm-IV(C16:2). Pretreatment with NodRm-III(C16:2) as well as unmodified chitooligosaccharides did not stimulate the dimer-forming enzyme. Roots preincubated with Rhizobium meliloti showed similar stimulation of the dimer-forming activity. Mutant strains unable to produce Nod factors did not enhance the hydrolytic activity. These results indicate a rapid feedback inactivation of Nod signals after their perception by the host plant alfalfa.
authors.affiliation: Institut des Sciences Vegetales, Centre National de la Recherche Scientifique, Avenue de la Terrasse, F-91198 Gif-sur-Yvette Cedex, France (C.S., M.S., E.K., A.K.).
authors.forename: C.
authors.initials: C
authors.lastname: Staehelin
authors.forename: M.
authors.initials: M
authors.lastname: Schultze
authors.forename: E.
authors.initials: E
authors.lastname: Kondorosi
authors.forename: A.
authors.initials: A
authors.lastname: Kondorosi