The effect of drought stress on the expression of key genes involved in the biosynthesis of triterpenoid saponins in liquorice (Glycyrrhiza glabra).
Glycyrrhiza glabra is an important medicinal plant throughout the world. Glycyrrhizin is a triterpenoid that is among the most important secondary metabolites produced by liquorice. Drought stress is proposed to enhance the levels of secondary metabolites. In this study, the effect of drought stress on the expression of important genes involved in the glycyrrhizin biosynthetic pathway was examined. Drought stress at the seedling stage was applied to 8-day-old plants using polyethylene glycol. Subsequently, the samples were collected 0, 4, 8 or 24 h post-treatment. At the adult plant stage, 10-month-old plants were subjected to drought stress by discontinuing irrigation. Subsequently, samples were collected at 2, 16 and 28 days after drought imposition (S(2d), S(16d) and S(28d), respectively). We performed semi-quantitative RT-PCR assays to evaluate the gene expression levels of sequalene synthase (SQS), β-amyrin synthase (bAS), lupeol synthase (LUS) and cycloartenol synthase (CAS) during stress. Finally, the glycyrrhizin content of stolons was determined via HPLC. The results revealed that due to osmotic stress, the gene expression levels of SQS and bAS were increased, whereas those of CAS were relatively unchanged at the seedling stage. At the adult plant stage, the expression levels of SQS and bAS were increased under drought stress conditions, whereas the gene expression level of CAS remained relatively constant. The glycyrrhizin content in stolons was increased only under severe drought stress conditions (S(28d)). Our results indicate that application of controlled drought stress up-regulates the expression of key genes involved in the biosynthesis of triterpenoid saponins and directly enhances the production of secondary metabolites, including glycyrrhizin, in liquorice plants.
Department of Biotechnology, Bu-Ali Sina University, Hamedan, Islamic Republic of Iran.
Vida
V
Nasrollahi
Department of Biotechnology, Bu-Ali Sina University, Hamedan, Islamic Republic of Iran. Electronic address: a.mirzaie@basu.ac.ir.
Asghar
A
Mirzaie-Asl
Department of Biotechnology, Bu-Ali Sina University, Hamedan, Islamic Republic of Iran.
Khosro
K
Piri
Department of Biotechnology, Bu-Ali Sina University, Hamedan, Islamic Republic of Iran.
Sonbol
S
Nazeri
Cereal Research Dept., Seed and Plant Improvement Institute, Karaj, Islamic Republic of Iran.
Rahim
R
Mehrabi
D002851:Chromatography, High Pressure Liquid; D055864:Droughts; D018506:Gene Expression Regulation, Plant; D006035:Glycyrrhiza / Q000201:enzymology / Q000378:metabolism*; D019695:Glycyrrhizic Acid / Q000378:metabolism; D019751:Intramolecular Transferases / Q000378:metabolism; D010946:Plants, Medicinal / Q000201:enzymology / Q000378:metabolism
D019695:Glycyrrhizic Acid; D019751:Intramolecular Transferases; C039924:2,3-oxidosqualene-beta-amyrin-cyclase; C117114:lupeol synthase; C021923:cycloartenol synthase
Drought stress; Gene expression; Glycyrrhiza glabra; Glycyrrhizin; Triterpenoid