Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: January 1, 2006
Publication Date: July 1, 2006
Citation: Krishnan, H.B., Bennett, J.O. 2006. Rhizobium-legume symboises: molecular signals elaborated by rhizobia that are important for nodulation. In: Gnanamanickam, Samuel S., editor. Plant-Associated Bacteria. First edition. The Netherlands:Springer. p. 57-104. Technical Abstract: Symbiotic nitrogen fixation provides legumes with nutrients for growth and development, obviating application of manufactured forms of reduced nitrogen, whose synthesis consumes vast amounts of fossil fuel. Initiation and continuation of the nodulation process is dependent upon a constant exchange of chemical signals between the host legume and the bacteria. Several bacterial and plant-derived components play a crucial role in establishing symbiotic association. Flavonoids released by the legumes and nodulation factors (Nod factors) secreted by the rhizobia are the two principal signal molecules involved in establishing symbisoses. In addition, other bacterial components such as secreted exopolysaccharides (EPS), membrane bound lipopolysaccharides (LPS), cyclic b-glucans, and nodulation outer proteins (Nops) play an integral role in nodule formation. This review examines the current state of our knowledge of various chemical signal molecules that are elaborated by the bacteria to establish symbioses with legumes.