Metabolic engineering of essential oil composition in Lavendula latifolia by altering expression of borneol diphosphate synthase

The volatile monoterpene metabolites camphor and borneol are considered undesired constituents of high-end lavender essential oils (EO) produced for the cosmetic industry. In plants, these metabolites are derived from borneol diphosphate (BPP), which itself results from the rearrangement of geranyl diphosphate (GPP) via a reaction catalyzed by the enzyme borneol diphosphate synthase (BPPS). Mahmoud group has recently cloned a unique BPPS gene from Lavandula x intermedia (the LiBPPS). However, the in planta role of this gene has not been evaluated. In this study, we aimed to confirm the in planta function of LiBPPS through its constitutive expression in sense and antisense in spike lavender (L. latifolia). To achieve this goal, the coding sequence of LiBPPS was placed under the control of the Cauliflower Mosaic Virus 35S (CaMV35S) promoter in sense and antisense orientations, and stably expressed in transformed L. latifolia plants via Agrobacterium-mediated transformation using hygromycin as a selectable marker. We evaluated the effect of LiBPPS overexpression (in sense and antisense) on abundance of BPPS transcript in transformed plants. As anticipated, overexpression of LiBPPS in sense resulted in an increase in BPPS mRNA levels, while overexpression of the gene in antisense led to a decrease in BPPS mRNA levels in transgenic plants. To determine whether altering the expression of BPPS influenced EO yield, and abundances of camphor, borneol and other monoterpenes, we analyzed the EO of the transgenic plants by gas chromatography mass spectrometry (GC-MS). Manipulating BPPS expression did not have a significant effect on oil yield. However, we observed a significant reduction in borneol and camphor, and a significant increase in the production of other EO constituents such as 1,8 cineole and limonene in 90.9 % of the BPPS-antisense plants relative to wild-type plants. Furthermore, meeting our expectations, 60% of the BPPS-sense plants produced higher levels of camphor and borneol, and lower amounts of other oil constituents including limonene and 1,8 cineole compared with wild-type plants. Results obtained in this study provide insight into the regulation of camphor production in lavenders, and confirm that monoterpene metabolism can be modified through genetic manipulation of terpene synthase expression.Science, Irving K. Barber Faculty of (Okanagan)Biology, Department of (Okanagan)Graduat