STRUCTURAL IDENTIFICATION OF THE LIPO-CHITIN OLIGOSACCHARIDE NODULATION SIGNALS OF RHIZOBIUM-LOTI

Rhirobium loti is a fast-growing Rhizobium species that has been descr ibed as a microsymbiont of plants of the genus Lotus. Nodulation studi es show that Lotus plants are nodulated by R. loti, but not by most ot her Rhizobiom strains, indicating that R. loti produces specific lipo- chitin oligosaccharides (LCOs) which are necessary for the nodulation of Lotos plants. The LCOs produced by five different Rhirobium loti st rains have been purified and were shown to be N-acetylglucosamine pent asaccharides of which the non-reducing residue is N-methylated and N-a cylated with cis-vaccenic acid (C18:1) or stearic acid (C18:0) and car ries a carbamoyl group. In one R. loti strain, NZP2037, an additional carbamoyl group is present on the non-reducing terminal residue. The m ajor class of LCO molecules is substituted on the reducing terminal re sidue with 4-O-acetylfucose. Addition of LCOs to the roots of Lotus pl ants results in abundant distortion, swelling and branching of the roo t hairs, whereas spot inoculation leads to the formation of nodule pri mordia.