Differential Expression of Three Oxidosqualene Cyclase mRNAs in Glycyrrhiza glabra

Abstract

Higher plants produce not only sterols but also various triterpenes, which are derived from six isoprene units, 1) and some triterpenes are further glycosylated to produce various triterpene saponins.2) These triterpenes and triterpene saponins are believed to participate in the plant defence systems against microbial pathogens or insects. [3][4][5] An interesting effect that has also been reported is that an exogenous triterpene saponin stimulates the growth of roots in several plants. 6,7) In addition to the benefit for plants themselves, these triterpenes and saponins are beneficial for human beings as medicines, sweeteners, detergents, and cosmetics. Although structural elucidation of triterpenes and saponins has been extensively studied, 1,2) our understanding about the regulation of their biosyntheses is quite limited at the molecular level. 8)Oxidosqualene cyclases (OSCs) catalyze the cyclization of 2,3-oxidosqualene, a common intermediate of both sterols and triterpenes. Lanosterol synthase, playing a crucial role in cholesterol biosynthesis, is a unique OSC in mammals. In higher plants, on the other hand, some OSCs responsible for triterpene biosynthesis co-exist with cycloartenol synthase corresponding to lanosterol synthase in mammals. 8,9) Up to now, cDNAs of OSCs including cycloartenol synthase, bamyrin synthase, lupeol synthase and multifunctional triterpene synthase have been functionally characterized from various plant species. 8) After cloning of these OSC genes, our interest has shifted the regulatory roles of these OSCs in triterpene and saponin biosyntheses in higher plants. 8,[10][11][12][13] In our study, licorice (Glycyrrhiza glabra L., Fabaceae) was used as a model plant to elucidate the regulation of triterpene biosyntheses in higher plants (Fig. 1). Cultured licorice cells lacked the ability to produce glycyrrhizin, a sweet oleanane-type triterpene saponin produced in the roots of the mother plant, but produced phytosterols and two structurally different triterpenoid constituents, soyasaponins and betulinic acid. 15,16) Glycyrrhizin is localized exclusively in the woody parts of the thickened roots and stolons, whereas soyasaponins, oleanane-type triterpene saponins, are localized mainly in the seeds and rootlets of licorice.17) On the other hand, the content of betulinic acid, a lupane-type triterpene, is high in the cork layer of thickened licorice roots. 15) cDNAs of cycloartenol synthase, an OSC involved in sterol biosynthesis, and b-amyrin synthase, an OSC involved in both glycyrrhizin and soyasaponin biosynthesis, have been cloned from G. glabra. 18,19) In addition to these two OSCs, the third OSC, lupeol synthase, which is responsible for the biosynthesis of betulinic acid, most likely exists in cultured licorice cells. In the present study, an OSC cDNA for lupeol synthase was isolated by heterologous hybridization with that of olive lupeol synthase, 20) and the patterns of mRNA expression of the three OSCs in the cultured cells and the intact plants of G. glabra were examined. ...

Compounds ofBetula PlatyphyllaCell Suspension Cultures in Response to Fungal Elicitor

“…It also shows the complex and divergent adaptation characteristics of oScs in response to fungal elicitation. Similar results have also been found in other research about oScs in response to external stress (9,10,11,12,15). For example, hayashi et al (11,12) investigated the differential regulation of three oSc mRnAs by MeJA and Gibberellin A3 (GA3) in cultured Glycyrrhiza glabra cells and pointed out that MeJA upregulated β-AS mRnA and soyasaponin biosynthesis but downregulated LUS mRnA expression, and GA3 downregulated β-AS mRnA but not LUS mRnA in the cultured cells.…”

Cloning and Functional Analysis of a &beta;-Amyrin Synthase Gene Associated with Oleanolic Acid Biosynthesis in <i>Gentiana straminea</i> M<small>AXIM.</small>

“…Thus we believe that GsAS1 is a monofunctional b-amyrin synthase, similar to a number of other plant species b-amyrin synthases. [26][27][28] According to the relationship of the distance in the phylogenetic tree, GsAS1 showed highly similarity with other bamyrin synthase of dicotyledonous plants. For all the OSCs mainly including b-amyrin synthase, lupeol synthase and cycloartenol synthase, there had been always two opinions in the evolution.…”

Cloning and Functional Characterization of Three Branch Point Oxidosqualene Cyclases from Withania somnifera (L.) Dunal

“…Co-occurrence of OSCs from both these groups for structuring different triterpenoid skeletons is often found in many plants such as G. glabra, Kalanchoe daigremontiana, Arabidopsis thaliana, etc. (33,42,43). Being juxtapositioned at a critical metabolic branch point, WsOSCs lead to the production of sterols, withanolides, and an array of triterpenoids.…”

“…These results are in consonance with the earlier studies in Glycyrrhiza glabra. Both lupeol synthase and ␤-amyrin synthase along with their triterpenoid products composed of betulinic acid and glycyrrhizin have been reported to be abundant in root and root nodules of G. glabra (33). Conversely, WsOSC/CS was found to be transcribing most in leaves, followed by nearly equal transcript abundance in stalk and berries, and a minimum in roots (Fig.…”