Lipochitooligosaccharides

Lipochitooligosaccharides (LCOs) are signaling molecules produced by rhizobia and, in some contexts, by arbuscular mycorrhizal fungi, that regulate symbiotic associations between microbes and plants. Chemically, they consist of a short chitooligosaccharide core—three to five N-acetylglucosamine units—linked to a fatty acyl chain at the nonreducing end. The lipid tail anchors the molecule and various substitutions on the oligosaccharide can fine‑tune activity.

Plant perception occurs mainly through LysM receptor-like kinases (LysM-RLKs), such as NFR1/NFR5 in Lotus japonicus and LYK3/NFP in Medicago truncatula. Binding of an LCO triggers early signaling events, including calcium spiking and downstream transcriptional responses, which coordinate root hair curling, infection thread formation, and nodule organogenesis in legumes. In arbuscular mycorrhizal symbiosis, structurally related Myc factors (LCOs) promote fungal colonization in many nonlegume plants as well.

Structural variation in LCOs, including acyl chain length, degree of saturation, and decorations such as acetylation or sulfation, determines host specificity. Sulfated or otherwise modified Nod factors are recognized by different legume hosts, influencing compatibility and nodulation efficiency.

Because of their central role in nodulation and mycorrhization, LCOs have been studied for agricultural applications, including the development of synthetic or microbial LCOs to enhance legume yields and reduce fertilizer inputs. Research continues to elucidate receptor complexes and signaling networks that govern LCO perception across plant species.