Molecular Biology of Secondary Metabolism: Case Study for Glycyrrhiza Plants



Licorice (roots and stolons of Glycyrrhiza plants) is one of the most important crude drugs from ancient times, and its major constituent is an oleanane-type triterpene saponin, glycyrrhizin, which is a well-known sweetener as well as a pharmaceutical. We are using Glycyrrhiza glabra (common licorice) as a model plant to elucidate the regulation of triterpene biosynthesis in higher plants. Cultured cells of G.glabra do not produce glycyrrhizin but produce two structurally different triterpenoid constituents, namely betulinic acid and soyasaponins. Glycyrrhizin is localized exclusively in the woody parts of thickened roots, whereas soyasaponins are localized mainly in the seeds and rootlets. Betulinic acid, a lupane-type triterpene, is localized in the cork layer of the thickened roots. The cultured licorice cells converted exogenously administered glycyrrhetinic acid, the aglycone of glycyrrhizin, into seven biotransformation products, but formation of glycyrrhizin was not detected among the biotransformation products. To elucidate the regulation of the triterpene biosyntheses in G.glabra, cDNAs of squalene synthase and three oxidosqualene cyclaces were cloned and characterized. mRNA levels of these enzymes were differently regulated in the cultured cells and intact plants of G.glabra. Exogenously applied methyl jasmonate (MeJA) stimulated soyasaponin biosynthesis in cultured cells, and mRNA levels of squalene synthase and β-amyrin synthase were upregulated by MeJA.


Betulinic Acid Glycyrrhetinic Acid Triterpene Saponin Licorice Root Oxidosqualene Cyclase 



This research is supported in part by Grants-in-Aid for Scientific Research to H. H. (07780500, 09771930, 13780470) from The Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.


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© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  1. 1.School of Pharmacy, Iwate Medical University, 2-1-1 NishitokutaYahabaJapan

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