CHARACTERIZATION OF RHIZOBIUM-TROPICI CIAT899 NODULATION FACTORS - THE ROLE OF NODH AND NODPQ GENES IN THEIR SULFATION

We have purified and characterized the nodulation factors produced by Rhizobium tropici CIAT899. This strain produces a large variety of nod ulation factors, these being a mixture of sulfated or nonsulfated pent a- or tetra-chitooligosaccharides to which any of six different fatty acyl moieties may be attached to nitrogen of the nanreducing terminal residue, In this mixture we have also found methylated or nonmethylate d lipo-chitin oligosaccharides. Here we describe a novel lipo-chitin-o ligosaccharide consisting of a linear backbone of 4 N-acetylglucosamin e residues and one mannose that is the reducing-terminal residue and b earing a C18:1 fatty acyl moiety on the nonreducing terminal residue. In addition, we have identified, cloned, and sequenced R. tropici nodH and nodPQ genes, generated mutations in the nodH and nodQ genes, and tested the mutant strains far nodulation in Phaseolus and Leucaena pla nts, Our results indicate that the sulfate group present in wildtype N od factors plays a major role in nodulation of Leucaena plants by stra in CIAT899 of R. tropici.