title: Lipopolysaccharides as a communication signal for progression of legume endosymbiosis.
abstract: Establishment of a successful symbiosis between rhizobia and legumes results from an elaborate molecular dialogue between both partners. Bacterial nodulation (Nod) factors are indispensable for initiating plant responses, whereas bacterial surface polysaccharides are important for infection progression and nodule development. The mutant ORS571-oac2 of Azorhizobium caulinodans, affected in its surface polysaccharides, provokes a defective interaction with its host Sesbania rostrata. ORS571-oac2 induced structures with retarded development and continued generation of infection centers and organ primordia, leading to multilobed ineffective nodules. Bacterial development throughout the interaction occurred without major defects. A functional bidirectional complementation was obtained upon coinfection of ORS571-oac2 and a Nod factor-deficient mutant, indicating that the Fix- phenotype of ORS571-oac2-induced nodules resulted from the absence of a positive signal from ORS571-oac2. Indeed, the Fix- phenotype could be complemented by coinoculation of ORS571-oac2 with lipopolysaccharides (LPSs) purified from A. caulinodans. Our data show that Nod factors and LPSs are consecutive signals in symbiosis. Nod factors act first to trigger the onset of the nodulation and invasion program; LPSs inform the plant to proceed with the symbiotic interaction and to develop a functional fixation zone.
authors.affiliation: Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology, Ghent University, Technologiepark 927, B-9052 Ghent, Belgium.
authors.forename: René
authors.initials: R
authors.lastname: Mathis
authors.forename: Frédérique
authors.initials: F
authors.lastname: Van Gijsegem
authors.forename: Riet
authors.initials: R
authors.lastname: De Rycke
authors.forename: Wim
authors.initials: W
authors.lastname: D'Haeze
authors.forename: Els
authors.initials: E
authors.lastname: Van Maelsaeke
authors.forename: Erin
authors.initials: E
authors.lastname: Anthonio
authors.forename: Marc
authors.initials: M
authors.lastname: Van Montagu
authors.forename: Marcelle
authors.initials: M
authors.lastname: Holsters
authors.forename: Danny
authors.initials: D
authors.lastname: Vereecke
mesh_terms: D020599:Azorhizobium caulinodans / Q000235:genetics / Q000378:metabolism*; D007887:Fabaceae / Q000378:metabolism* / Q000382:microbiology*; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D008070:Lipopolysaccharides / Q000378:metabolism*; D009154:Mutation; D010641:Phenotype; D015398:Signal Transduction; D013559:Symbiosis / Q000235:genetics / Q000502:physiology*
chemical_list: D008070:Lipopolysaccharides