[Nod factors, chemical signal exchange between bacteria and leguminous plants in nitrogen fixing symbiosis].
The early steps of the nitrogen-fixing symbiosis between plant legumes and soil bacteria (rhizobium) are mediated by an exchange of chemical signals between the two partners. Upon gene activation by plant root secretions (flavonoids), bacteria synthesize lipochitooligomers (called Nod Factors, NFs) that induce root hair deformations, cortical cell divisions, allow bacterial entry and produce nodule organogenesis at nano to picomole concentrations. Substitutions occurring on the lipochitooligosaccharide core are essential for recognition and activity. Biosynthesis of these molecules is now fully dissected, by looking at the structural changes in NFs induced by gene mutation or gene transfers. From the biodiversity studies of NFs, it appears that their structures belong with the phylogenetic evolution of plants, rather than that of bacteria, suggesting a coevolution of symbiotic bacteria with their plant receptors. Some preliminary and indirect observations indicate that similar molecules seem to exist in non-legumes plants, in batrachians and fishes beeing possibly involved in their embryogenesis, but they are probably at at a so low concentration that all attempts to detect them directly fail up to now.
Promé
J C
JC
Signaux Biologiques et Spectrométrie de Masse, Institut de Pharmacologie et Biologie Structurale, Toulouse.
D002240:Carbohydrate Sequence; D008070:Lipopolysaccharides / Q000378:metabolism*; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
D008070:Lipopolysaccharides; C092736:Nod factor, Rhizobium leguminosarum
Les facteurs Nod, éléments de reconnaissance entre bactéries et plantes légumineuses lors de leur symbiose fixatrice d'azote.