Primary and Secondary Metabolites in Lotus japonicus

Lotus japonicus is a leguminous modelplant usedto gain insight into plant physiology, stress response, and especiallysymbiotic plant-microbe interactions, such as root nodule symbiosisor arbuscular mycorrhiza. Responses to changing environmental conditions,stress, microbes, or insect pests are generally accompanied by changesin primary and secondary metabolism to account for physiological needsor to produce defensive or signaling compounds. Here we provide anoverview of the primary and secondary metabolites identified in L. japonicus to date. Identification of the metabolitesis mainly based on mass spectral tags (MSTs) obtained by gas chromatographylinked with tandem mass spectrometry (GC-MS/MS) or liquid chromatography-MS/MS(LC-MS/MS). These MSTs contain retention index and mass spectralinformation, which are compared to databases with MSTs of authenticstandards. More than 600 metabolites are grouped into compound classessuch as polyphenols, carbohydrates, organic acids and phosphates,lipids, amino acids, nitrogenous compounds, phytohormones, and additionaldefense compounds. Their physiological effects are briefly discussed,and the detection methods are explained. This review of the exisitingliterature on L. japonicus metabolites provides avaluable basis for future metabolomics studies.