INDUCTION OF NODULE PRIMORDIA ON PHASEOLUS AND ACACIA BY LIPO-CHITIN OLIGOSACCHARIDE NODULATION SIGNALS FROM BROAD-HOST-RANGE RHIZOBIUM STRAIN GRH2

Rhizobium wild-type strain GRH2 was originally isolated from the tree, Acacia cyanophylla, and has a broad host-range which includes herbace ous legumes, such as Phaseolus and Trifolium species. Here we show tha t strains of Rhizobium sp. GRH2, into which heterologous nodD alleles have been introduced, produce a large diversity of both sulphated and non-sulphated lipo-chitin oligosaccharides (LCOs). Most of the molecul ar species contain an N-methyl group on the reducing-terminal N-acetyl -glucosamine. The LCOs vary in the nature of the fatty acyl chain and in the length of the chitin backbone. The majority of the LCOs have an oligosaccharide chain length of five GlcNAc residues, but a few are o ligomers having six GlcNAc units. LCOs purified from GRH2 are able to induce root hair formation and deformation on Acacia cyanophylla and A . melanoxylon plants. We show that an N-vaccenoyl-chitopentaose bearin g an N-methyl group is able to induce nodule primordia on Phaseolus vu lgaris, A. cyanophylla, and A. melanoxylon, indicating that for these plants an N-methyl modification is sufficient for nodule primordia ind uction.