Terpene Profiling and Characterization of Terpene Synthases in the Aerial Parts of Aucklandia costus

Objective: The roots of Aucklandia costus are traditionally used as medicine and as the main source of A. costus essential oil, with versatile applications in a lot of fields, which has led to the overexploitation of this medicinal plant resource. To address this problem, this study phytochemically investigated the aerial biomass of A. costus, which remains underutilized after harvest, to evaluate its potential as a new source of medicinal components besides the roots. Furthermore, monoterpene synthases and sesquiterpene synthases of A. costus were studied, as its root essential oil is rich in mono- and sesquiterpenoids. Methods: Terpenoids were analyzed and characterized using HPLC, chromatographic separation, HR-MS, NMR, and ECD. The ROS-scavenging activity of the isolated compounds was measured with a DCFH-DA probe in HepG2 cells. Candidate terpene synthases were cloned from cDNA and investigated through phylogenetic analysis, qRT-PCR, and in vitro enzyme assays using geranyl diphosphate (GPP) and farnesyl diphosphate (FPP). Results: Costunolide and dehydrocostus lactone are two marker constituents of the A. costus root. Quantitative comparison of the content of these two compounds between the aerial biomass and roots of A. costus indicated that the contents of costunolide and dehydrocostus lactone in aerial parts are about 15% and 8% of those in the roots, respectively. Four previously undescribed guaianolides 1–4, which are structural analogues to dehydrocostus lactone, were isolated from the aerial biomass, with compound 1 showing a pronounced ROS-scavenging effect in HepG2 cells. Four terpene synthase genes, AcTPS1–AcTPS4, were obtained. Expression profiling indicated the aerial enrichment of all four genes. In vitro, AcTPS1–AcTPS3 accepted GPP and FPP to different extents and generated mono- and/or sesquiterpene products. AcTPS4 was identified as a GPP-specific multiproduct monoterpene synthase. AcTPS3 and AcTPS4 may be related to some reported monoterpenes from the essential oil of the root of A. costus. Conclusions: The aerial parts contain both a sesquiterpene-lactone chemical basis related to the traditionally used root and a diverse terpene-biosynthetic capacity may associated with A. costus essential oil.