Department of Biotechnology, Faculty of Agricultural Sciences, University of Guilan, Rasht, 4199613776, Iran.
Department of Plant Biotechnology, Faculty of Life Science and Biotechnology, Shahid Beheshti University, G.C., Tehran, Iran.
Protoplasma. 2019 May;256(3):827-837. doi: 10.1007/s00709-018-01340-4. Epub 2019 Jan 8.
Licorice is a well-known medicinal plant, containing various secondary metabolites of triterpenoid and phenolic families. The aim of this study is to evaluate the effect of salinity stress on the expression of key genes involved in the biosynthetic pathway of triterpenoids such as glycyrrhizin, betulinic acid, soyasaponins, and phytosterols in licorice root, as well as providing a phonemic platform to characterize antioxidant properties, glycyrrhizin, and total phenolic content. This study also includes measuring the gene expression level and glycyrrhizin content in leaves and roots of control plants. The studied genes included squalene synthase (SQS1 and SQS2), β-amyrin synthase (bAS), lupeol synthase (LUS), cycloartenol synthase (CAS), β-amyrin 11-oxidase (CYP88D6), and β-amyrin 24-hydroxylase (CYP93E6). Our results revealed that all of the mentioned genes were upregulated following the stress condition with different transcription rates. The highest increase (12-fold) was observed for the expression of the LUS gene, which is related to the betulinic acid pathway. Also, the highest content of glycyrrhizin was observed at 72 h post-treatment, which was consistent with the upregulated transcription levels of the glycyrrhizin pathway genes especially SQS1 and CYP88D6 at the same time. Correlation and stepwise regression analysis proved the key role of SQS1 gene in the biosynthetic pathway of glycyrrhizin. Antioxidant activity and phenolic content also were increased following stress condition. A comparison between the expression levels of SQS1 and other genes involved in the production of glycyrrhizin, phytosterols, and soyasaponins revealed a similar transcription trend, which shows the gene expression in the roots was significantly higher than the leaves. In contrast, SQS2 and LUS genes displayed a higher expression in leaf tissues. The genes related to betulinic acid biosynthetic pathway exhibited an expression rate different from other triterpenoid pathway genes, which could be observed in the leaves and roots of control plants and the roots of salt-treated plants. Furthermore, results showed that these two SQS genes have different expression rates due to different plant tissues (roots and leaves) and stress conditions. Importantly, in contrast to previous reports, we detected the glycyrrhizin in leaf tissues. This result may indicate the presence of a different genetic background in native Iranian licorice germplasm.
甘草是一种广为人知的药用植物，其含有各种三萜类和酚类家族的次生代谢产物。本研究旨在评估盐胁迫对甘草根中参与三萜生物合成途径的关键基因（如甘草酸、白桦脂酸、大豆皂苷和植物甾醇）表达的影响，并为表征抗氧化特性、甘草酸和总酚含量提供一个音系平台。本研究还包括测量对照植物叶片和根中的基因表达水平和甘草酸含量。所研究的基因包括鲨烯合酶（SQS1 和 SQS2）、β-香树脂醇合酶（bAS）、羽扇豆醇合酶（LUS）、环阿屯醇合酶（CAS）、β-香树脂醇 11-氧化酶（CYP88D6）和β-香树脂醇 24-羟化酶（CYP93E6）。我们的结果表明，所有提到的基因在不同的转录速率下均被上调。LUS 基因的表达上调最为明显（12 倍），这与白桦脂酸途径有关。同时，甘草酸含量在处理后 72 小时达到最高，这与甘草酸途径基因（特别是 SQS1 和 CYP88D6）的转录水平上调一致。相关性和逐步回归分析证明了 SQS1 基因在甘草酸生物合成途径中的关键作用。抗氧化活性和酚类含量也在胁迫条件下增加。SQS1 基因与参与甘草酸、植物甾醇和大豆皂苷生产的其他基因的表达水平进行比较，显示出相似的转录趋势，这表明根部的基因表达明显高于叶片。相反，SQS2 和 LUS 基因在叶片组织中表达较高。与其他三萜类途径基因不同，参与白桦脂酸生物合成途径的基因在对照植物的叶片和根以及盐处理植物的根中均有表达。此外，结果表明，由于不同的植物组织（根和叶）和胁迫条件，这两个 SQS 基因的表达率不同。重要的是，与以前的报告不同，我们在叶片组织中检测到了甘草酸。这一结果可能表明伊朗本土甘草种质资源具有不同的遗传背景。
