GC-MS analysis of sesquiterpene products of sunflower germacrene A synthases HaGAS1 and HaGAS2 compared to germacrene A standard produced by LsLTC2 from lettuce. (a) In vitro enzyme-substrate reactions using purified recombinant HaGAS1 or HaGAS2 with the substrate FDP showing β-elemene (peak 1), the cope-rearrangement product of germacrene A. Germacrene A: standard produced by expression of LsLTC2 (L. sativa germacrene A synthase 2, chromatogram not true to scale); negative control: incubation of FDP with total proteins isolated from E. coli without plasmid. (b) In vivo products from gene expression in yeast showing β-elemene (peak 2) and germacrene A (peak 3). Negative control: yeast strain carrying the empty vector. Differences between (a) and (b) were caused by the use of different injection port temperatures.