Infection and nodulation signalling in Rhizobium-Phaseolus vulgaris symbiosis

During the Rhizobium-legume symbiosis, a mutual exchange of signalling molecules occurs. Distinct oligo- and polysaccharides are involved in nodule formation and rhizobial invasion. The common bean is a promiscuous host plant that can be nodulated by a wide range of rhizobia. Reviewing the literature on nodulation suggests that the Nod factor oligosaccharide backbone of bean-nodulating rhizobia does not require a specific attached group, except for the acyl chain at the non-reducing end. However, in Rhizobium strains that elicit nitrogen-fixing nodules on Phaseolus vulgaris and that produce methylated Nod factors, NodS mediated decorations are indispensable for invasion and/or subsequent nitrogen-fixation. Finally, we present a model that links the pathways for methylation and sulphation in nodule signalling and invasion processes.