RHIZOBIAL LIPO-OLIGOSACCHARIDE NODULATION FACTORS - MULTIDIMENSIONAL CHROMATOGRAPHIC ANALYSIS OF SYMBIOTIC SIGNALS INVOLVED IN THE DEVELOPMENT OF LEGUME ROOT-NODULES

Nod factors are a group of biologically active oligosaccharide signals that are secreted by symbiotically competent bacteria of the family R hizobiaceae. Their biosynthesis is determined by rhizobial nodulation (nod) genes, and is specifically induced in response to flavonoids sec reted from the roots of host leguminous plants, The biological activit y of Nod factors on these host legumes dramatically mimics the early d evelopmental symptoms of the Rhizobium-legume symbiosis including, amo ngst other effects, root hair deformations and nodule initiation, Stru cturally, all Nod factors are short oligomers of beta-1,4-linked N-ace tylglucosamine residues [usually degree of polymerization (dp) 4 or 5] that are N-acylated on the distal glucosamine, This common 'core' str ucture may be modified by a number of species-specific substituents on the distal or reducing sugars, These modifications are governed by rh izobial host specificity nod genes, The biological activity of purifie d Nod factors mirrors this host specificity, indicating that the symbi otic host range of individual Rhizobium species is, at least partially , determined by the variety of Nod factors they are able to produce. H ere we describe techniques that are universally applicable to the extr action, chromatographic separation and identification of Nod factors, We have applied these techniques to Nod factors from the broad-host-ra nge species Rhizobium fredii USDA257 and Rhizobium spp. NGR234, and th e more narrow-host-range Bradyrhizobium japonicum USDA110, and have id entified a group of novel, relatively hydrophilic Nod factors from the NGR234 species that may have implications for Nod factor biosynthesis .