Bacteria belonging to the genera Rhizobium, Bradyrhizobium, and Azorhizobium, collectively known as rhizobia, penetrate the roots (or adventitious roots) of their leguminous host plants via tubular... Show moreBacteria belonging to the genera Rhizobium, Bradyrhizobium, and Azorhizobium, collectively known as rhizobia, penetrate the roots (or adventitious roots) of their leguminous host plants via tubular structures, the infection threads. During infection of the host plant they trigger the formation of a new organ, the root nodule, in which a differentiated form of rhizobia, the bacteroid, fixes nitrogen into ammonia, which can then be used by the plant. This review presents an update of the recent literature on the molecular biology of the infection and nodulation of plants by rhizobia, with special emphasis on results pertinent to other plant-microbe interactions. Particular attention is given to determinants of host specificity such as flavonoid and lipo-chitin oligosaccharide signal molecules. Show less
Rhizobium bacteria produce certain lipo-oligosaccharides (modified chitin oligomers) after induction of nodulation (nod) gene transcription by the host plant. The function of the rhizobial nod... Show moreRhizobium bacteria produce certain lipo-oligosaccharides (modified chitin oligomers) after induction of nodulation (nod) gene transcription by the host plant. The function of the rhizobial nod genes in the biosynthesis of these lipo-oligosaccharides, focusing on their host specific aspects, is discussed. The lipo-oligosaccharides can elicit various responses in the host plants, like the formation of pre-infection threads and nodule meristems. Speculating on their function in plant morphogenesis the question is raised: do the rhizobial lipo-oligosaccharides resemble unknown plant signal molecules? Show less