Perception and signal transduction of rhizobial NOD factors

Soil bacteria belonging to genera Rhizobium, Bradyrhizobium, Allorhizobium, Azorhizobium, Mesorhizobium, and Sinorhizobium are able to induce nodule f ormation on the roots of leguminous plants. In the differentiated root nodu les bacteria fix as bacteroids atmospheric nitrogen and deliver it to the h ost plant. The interaction between bacteria and host plant starts with a co mplex signal exchange. After induction by plant flavonoids, rhizobia synthe size and secrete lipo-chitooligosaccharides (LCOs), known as Nod factors, w hich induce morphological changes and expression of early nodulin genes in the roots of host plants. Specific recognition of Nod factors by host plant s and early stages of signal transduction are discussed.