NODZ OF BRADYRHIZOBIUM EXTENDS THE NODULATION HOST-RANGE OF RHIZOBIUMBY ADDING A FUCOSYL RESIDUE TO NODULATION SIGNALS

The nodulation genes of rhizobia are involved in the production of the lipo-chitin oligosaccharides (LCO), which are signal molecules requir ed for nodule formation, A mutation in nodZ of Bradyrhizobium japonicu m results in the synthesis of nodulation signals lacking the wild-type 5-O-methylfucose residue at the reducing-terminal N-acetylglucosamine , This phenotype is correlated with a defective nodulation of siratro (Macroptilium atropurpureum), Here we show that transfer of nodZ to Rh izobium leguminosarum biovar (bv) viciae, which produces LCOs that are not modified at the reducing-terminal N-acetylglucosamine, results in production of LCOs with a fucosyl residue on C-6 of the reducing-term inal N-acetylglucosamine. This finding, together with in vitro enzymat ic assays, indicates that the product of nodZ functions as a fucosyltr ansferase, The transconjugant R. leguminosarum strain producing fucosy lated LCOs acquires the capacity to nodulate M. atropurpureum, Glycine soja, Vigna unguiculata and Leucaena leucocephala, Therefore, nodZ ex tends the narrow host range of R. leguminosarum bv. viciae to include various tropical legumes, However, microscopic analysis of nodules ind uced on siratro shows that these nodules do not contain bacteroids, sh owing that transfer of nodZ does not allow R. leguminosarum to engage in a nitrogen-fixing symbiosis with this plant.