Identification and Functional Analysis of the Fragrance Terpene Synthase Gene <i>PpTPS5</i> in <i>Pyrethrum parthenium</i>

Pyrethrum parthenium, a perennial herb from the genus Pyrethrum within the Asteraceae family, is known for its potent fragrance and significant economic value. Nevertheless, the mechanisms involved in the synthesis and regulation of its floral fragrance compounds remain unclear. This study used gas chromatography-mass spectrometry (GC-MS) to analyze the volatile compounds in five parts of P. parthenium: tubular flowers, ligulate flowers, sepals, receptacles, and leaves. The results showed that the volatile aromatic components include terpenes such as camphor, α-pinene, camphene, d-limonene, β-caryophyllene, and β-farnesene, with camphor being the main volatile compound. Based on the transcriptome data of tubular flowers of P. parthenium, a terpene synthase gene, PpTPS5, was identified. The results of both in vitro and in vivo enzymatic assays demonstrated that PpTPS5 functions as a bifunctional terpene synthase gene. The qRT-PCR results showed that the gene expression pattern of PpTPS5 is correlated with the release pattern of the corresponding terpene aromatic compounds in P. parthenium. Subcellular localization and inhibitor experiments indicated that PpTPS5 functions in the cytosol. Additionally, dual-luciferase and electrophoretic mobility shift assay (EMSA) assays revealed that PpMYB9 can bind to the promoter of PpTPS5 to regulate the biosynthesis of terpenoids. In conclusion, the results of this study provide a theoretical basis for further exploration of the transcriptional regulation of terpene floral fragrance compounds in P. parthenium.