CHANGES IN THE GLYCOSYLATION PATTERN AT THE REDUCING END OF AZORHIZOBIAL NOD FACTORS AFFECT NODULATION EFFICIENCY

The Nod factors of Azorhizobium caulinodans ORS571 are lipo-chitooligo saccharides that at the reducing end can be unsubstituted, substituted with a L-fucosyl group, with a D-arabinose, or with both groups at th e same time. These lipo-chitooligosaccharides are the compounds produc ed by the bacteria during the signal exchange with their host plant at the onset of the nodulation process. By the use of wild-type and muta nt strains, the role of the different Nod factor glycosylations on the nodulation behavior was checked. The mere presence of the D-arabinosy l group at the reducing end of the lipo-chitooligosaccharides resulted in a higher number of nodules on roots of Sesbania rostrata, whereas the presence or absence of L-fucose had no effect. The situation is th e opposite in other tropical legumes that respond to A. caulinodans OR S571: the L-fucose is the major determinant of nodulation, whereas the presence of D-arabinose is less significant. By the use of a beta-glu curonidase reporter fusion, A. caulinodans ORS571 was shown to coloniz e nodules or nodule-like tissues induced on cowpea and bean, respectiv ely. (C) 1998 Federation of European Microbiological Societies. Publis hed by Elsevier Science B.V.