Structural identification of the iipo‐chitin oligosaccharide nodulation signals of Rhizobium loti

Abstract

Rhizobium loti is a fast-growing Rhizobium species that has been described as a microsymbiont of plants of the genus Lotus. Nodulation studies show that Lotus plants are nodulated by R loti, but not by most other Rhizobium strains, indicating that R. loti produces specific lipo-chitin oligosaccharides (LCOs) which are necessary for the nodulation of Lotus plants. The LCOs produced by five different Rhizobium ioti strains have been purified and were shown to be N-acetylglucosamine pentasaccharides of which the non-reducing residue is N-methylated and N-acylated with c/s-vaccenic acid (C18:1) or stearic acid (C18:O) and carries a carbamoyl group. In one R. loti strain, NZP2037, an additional carbamoyl group is present on the non-reducing terminal residue. The major class of LCO molecules is substituted on the reducing terminal residue with 4-O-acetylfucose. Addition of LCOs to the roots of Lotus plants results in abundant distortion, swelling and branching of the root hairs, whereas spot inoculation leads to the formation of nodule primordia.