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Int. J. Mol. Sci. 2015, 16(2), 3564-3578;

Characterisation of Two Oxidosqualene Cyclases Responsible for Triterpenoid Biosynthesis in Ilex asprella

Research Center of Chinese Herbal Resource Science and Engineering, Key Laboratory of Chinese Medicinal Resource from Lingnan, Guangzhou University of Chinese Medicine, Guangzhou 510006, China
The Key Laboratory of Technology of Breaking Cell Wall and Application in Chinese Medicine Decoction Pieces, Zhongshan Zhongzhi Pharmaceutical Group, Zhongshan 528437, China
Authors to whom correspondence should be addressed.
Academic Editor: Ute Roessner
Received: 2 December 2014 / Accepted: 27 January 2015 / Published: 5 February 2015
(This article belongs to the Special Issue Metabolomics in the Plant Sciences)
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Ilex asprella, a plant widely used as a folk herbal drug in southern China, produces and stores a large amount of triterpenoid saponins, most of which are of the α-amyrin type. In this study, two oxidosqualene cyclase (OSC) cDNAs, IaAS1 and IaAS2, were cloned from the I. asprella root. Functional characterisation was performed by heterologous expression in the yeast Saccharomyces cerevisiae. Analysis of the resulting products by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) showed that both genes encode a mixed amyrin synthase, producing α-amyrin and β-amyrin at different ratios. IaAS1, which mainly produces α-amyrin, is the second triterpene synthase so far identified in which the level of α-amyrin produced is ≥80% of total amyrin production. By contrast, IaAS2 mainly synthesises β-amyrin, with a yield of 95%. Gene expression patterns of these two amyrin synthases in roots and leaves of I. asprella were found to be consistent with the content patterns of total saponins. Finally, phylogenetic analysis and multiple sequence alignment of the two amyrin synthases against several known OSCs from other plants were conducted to further elucidate their evolutionary relationship. View Full-Text
Keywords: triterpene synthase; amyrin; Ilex asprella; gene cloning and expression triterpene synthase; amyrin; Ilex asprella; gene cloning and expression

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Zheng, X.; Luo, X.; Ye, G.; Chen, Y.; Ji, X.; Wen, L.; Xu, Y.; Xu, H.; Zhan, R.; Chen, W. Characterisation of Two Oxidosqualene Cyclases Responsible for Triterpenoid Biosynthesis in Ilex asprella. Int. J. Mol. Sci. 2015, 16, 3564-3578.

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