Formation of Lipochitin Oligosaccharide Signaling Molecules

Abstract

Lipochitinoligosaccharides (LCOs) are made up of an N-acetylglucosamine backbone of four to five monosaccharide units bearing at it nonreducing end an N-linked fatty acyl chain. They are partly secreted as signaling molecules and are playing key roles in plant-root symbioses. However, these molecules are synthesized at the inner membrane and accumulated there. Therefore, they can be considered as membrane-associated lipids. We summarize in this chapter the outstanding contributions performed in the 1990s to the biosynthesis of these compounds in the rhizobium background, where the LCOs are named Nod factors. Recent work provided a new perspective to the time course of this complex biosynthetic pathway, and we will particularly elaborate it here. Finally, since Nod factor-like molecules were attested to be synthesized by the mycor-rhiza, the actual trend is to understand their synthesis in fungi and to extend their inventory within this reign. Even if significant efforts are deployed nowadays, only little has been published on this topic. We aim to summarize these contributions to open up new avenues of investigation enabled by rapid genomic analysis.