The Host-Specific Role of Chemical Modifications at the Reducing Terminus of Lipo-Chitin Oligosaccharides

Abstract

Signal molecules which determine the host specificity of rhizobia for particular leguminous plants include flavonoids secreted by the host plant roots and the bacterial lipo-chitin oligosaccharides (LCOs). This presentation will mainly focuss on the role of the LCOs. For instance, a highly unsaturated fattyl moiety of LCOs plays a major role in the specificity of rhizobia which associate with indeterminate-nodulating plants. The genes nodF (acyl carrier protein), nodE (β-ketoacylsynthase) and nodA (acyl transferase) are involved in the production of LCOs containing such a special fatty acids. For determinate nodulating plants a fucosyl residue (located at the reducing N-acetylglucosamine residue of LCOs) plays a major role in determining specificity. The nodZ gene which is present in various rhizobia such as Bradyrhizobium japonicum, Rhizobium loti and R.etli, is a fucosyltransferase involved in the addition of this fucose (Lopez-Lara et al, 1996). The role of other determinants of host specificity, such as nodX and nolL will be discussed.