Volatile Profiling and Transcriptome Sequencing Provide Insights into the Biosynthesis of α-Pinene and β-Pinene in Liquidambar formosana Hance Leaves.

Liquidambar formosana Hance is a pinene-rich deciduous plant species in the Altingiaceae family that is used as a medicinal plant in China. However, the regulatory mechanisms underlying α-pinene and β-pinene biosynthesis in L. formosana leaves remain unknown. Here, a joint analysis of the volatile compounds and transcriptomes of L. formosana leaves was performed to comprehensively explore the terpene synthase (TPS) that may participate in α-pinene and β-pinene biosynthesis. Headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) jointly detected volatile L. formosana leaves. Trees with high and low levels of both α-pinene and β-pinene were defined as the H group and L group, respectively. RNA sequencing data revealed that DXR (1-deoxy-D-xylulose-5-phosphate reductoisomerase), HDS [(E)-4-hydroxy-3-methylbut-2-eny-l-diphosphate synthase], and TPS may be the major regulators of monoterpenoid biosynthesis. We identified three TPSs ( LfTPS1, LfTPS2 , and LfTPS3 ), which are highly homologous to α-pinene and β-pinene synthases of other species in phylogenetic analysis. Four TPS genes ( LfTPS1 , LfTPS2 , LfTPS4 , LfTPS5 ) may be critically involved in the biosynthesis and regulation of α-pinene and β-pinene in L. formosana . Bioinformatic and transcriptomic results were verified using quantitative real-time PCR. We identified LfTPS1, LfTPS2 as candidate genes for α-pinene and β-pinene biosynthesis that significantly improve the yield of beneficial terpenoids.