Comparison of plant-based expression platforms for the heterologous production of geraniol

We compared the ability of different plant-based expression platforms to produce geraniol, a key metabolite in the monoterpenoid branch of the terpenoid indole alkaloid biosynthesis pathway. A geraniol synthase gene isolated from Valeriana officinalis (VoGES) was stably expressed in different tobacco systems. Intact plants were grown in vitro and in the greenhouse and were used to generate cell suspension and hairy root cultures. VoGES was also transiently expressed in N. benthamiana. The highest geraniol content was produced by intact transgenic plants grown in vitro (48 mu g/g fresh weight, fw), followed by the transient expression system (27 mu g/g fw), transgenic plants under hydroponic conditions in the greenhouse and cell suspension cultures (16 mu g/g fw), and finally hairy root cultures (9 mu g/g fw). Differences in biomass production and the duration of cultivation resulted in a spectrum of geraniol productivities. Cell suspension cultures achieved a geraniol production rate of 1.8 mu g/g fresh biomass per day, whereas transient expression produced 5.9 mu g/g fresh biomass per day (if cultivation prior to agroinfiltration is ignored) or 0.5 mu g/g fresh biomass per day (if cultivation prior to agroinfiltration is included). The superior productivity, strict process control and simple handling procedures available for transgenic cell suspension cultures suggest that cells are the most promising system for further optimization and ultimately for the scaled-up production of geraniol.