Perception and Signal Transduction of Rhizobial NOD Factors

Referee: Dr. Gary Stacey, Director, Center for Legume Research, Department of Microbiology, M409 Walters Life Science Bldg., University of Tennessee, Knoxville, TN 37966-0845 Soil bacteria belonging to genera Rhizobium, Bradyrhizobium, Allorhizobium, Azorhizobium, Mesorhizobium, and Sinorhizobium are able to induce nodule formation on the roots of leguminous plants. In the differentiated root nodules bacteria fix as bacteroids atmospheric nitrogen and deliver it to the host plant. The interaction between bacteria and host plant starts with a complex signal exchange. After induction by plant flavonoids, rhizobia synthesize and secrete lipo-chitooligosaccharides (LCOs), known as Nod factors, which induce morphological changes and expression of early nodulin genes in the roots of host plants. Specific recognition of Nod factors by host plants and early stages of signal transduction are discussed.