Identification and Functional Characterization of Sesquiterpene Synthases from<i>Xanthium strumarium</i>
作者:Yuanjun Li、Fangfang Chen、Zhenqiu Li、Changfu Li、Yansheng Zhang
DOI:10.1093/pcp/pcw019
日期:2016.3
Xanthium strumarium synthesizes various pharmacologically active sesquiterpenes. The molecular characterization of sesquiterpene biosynthesis in X. strumarium has not been reported so far. In this study, the cDNAs coding for three sesquiterpene synthases (designated as XsTPS1, XsTPS2 and XsTPS3) were isolated using the X. strumarium transcriptome that we recently constructed. XsTPS1, XsTPS2 and XsTPS3 were revealed to have primary activities forming germacrene D, guaia-4,6-diene and germacrene A, respectively, by either ectopic expression in yeast cells or purified recombinant protein-based in vitro assays. Quantitative real-time PCRs and metabolite analysis for the different plant parts showed that the transcript abundance of XsTPS1–XsTPS3 is consistent with the accumulation pattern of their enzymatic products, supporting their biochemical functions in vivo. In particular, we discovered that none of the XsTPS2 product, guaia-4,6-diene, can be detected in one of the X. strumarium cultivars used in this study (it was named the Hubei-cultivar), in which a natural deletion of two A bases in the XsTPS2 cDNA disrupts its activity, which further confirmed the proposed biochemical role of XsTPS2 in X. strumarium in vivo.
Xanthium strumarium合成多种具有药理活性的倍半萜。迄今为止,尚未有X. strumarium倍半萜生物合成的分子特征报道。在这项研究中,我们利用最近构建的X. strumarium转录组分离了编码三种倍半萜合成酶(分别命名为XsTPS1、XsTPS2和XsTPS3)的cDNA。通过在酵母细胞中的异位表达或纯化的重组蛋白体外检测,发现XsTPS1、XsTPS2和XsTPS3分别具有形成germacrene D、guaia-4,6-diene和germacrene A的主要活性。对不同植物部位的定量实时PCR和代谢产物分析表明,XsTPS1-XsTPS3的转录丰度与其酶促产物的积累模式一致,支持了其在体内的生化功能。特别是,我们发现,在用于本研究的X. strumarium栽培品种(名为湖北栽培品种)中,无法检测到XsTPS2产物guaia-4,6-diene,该品种中XsTPS2 cDNA的两个A碱基天然缺失,从而破坏了其活性,这进一步证实了XsTPS2在X. strumarium体内所发挥的生化作用。