The pivotal role of tandem mass spectrometry in structural determinations of Nod factors produced by Rhizobia: Nod factors produced by wild-type strains of Mesorhizobium huakii and Rhizobium sp. mus10

Abstract

Nod factors are signalling molecules secreted by bacteria of the Rhizobium family that plays an important role in initiating the early events of the nitrogen-fixing symbiosis between Rhizobia and legumes. They possess a lipochitooligomeric structure decorated by several functional groups. The structural details are essential for their specific recognition by plants and for switching on a genetic mechanism leading to the formation of nodules. Mass spectrometry is now able to fully characterise these molecules, even within mixtures and on minute amounts. It opens the possibility to study Nod factors from wild-type low-producing strains. It was demonstrated that Nod factors from the wild-type strain of Mesorhizobium huakii are almost the same as those produced by a genetically engineered over-producing strain. Rhizobium sp. mus10 is an Indian strain that nodulates the plant Sesbania. It was found that several Nod factors produced by this strain are identical to those produced by African strains that nodulate Sesbania species. However, two other Nod factors possessed new structural features. This synthetic possibility was probably acquired by the Rhizobium sp. mus10 strain by evolution in a different environment.