Genetically modified tobacco (Nicotiana tabacum) plants for an increased production of wax esters

Wax esters (WE) are naturally occurring lipids consisting of a fatty acid bound to a fatty alcohol with an ester bond. As an alternative to petrochemicals, plant-derived WE:s are of considerable commercial interest as lubricants, but have in recent years also received great attention for their potential as a starting material for bio-fuel production. It was recently shown that WE:s can be overproduced in stably transformed tobacco plants carrying a gene fusion between two genes encoding a fatty acid reductase (FAR) and wax ester synthase (PES), thus forming a single WE-synthesizing enzyme (Aslan 2015). Chloroplast- directed overexpression of the fusion enzyme led to an 8-fold induction of WE levels (0.15 % by dry weight) in transgenic plants (Aslan et al. 2015). However, this work also revealed negative growth effects, likely from high levels of the intermediate metabolite fatty alcohol, possibly inhibiting higher levels of WE production. The present study was undertaken to investigate the possibility of increasing the WE levels in transgenic plants even further. Through different genetic approaches, a small number of transgenic tobacco lines overexpressing both FAR and PES were demonstrated to have a higher survival rate and a new phenotype compared to previous transformants. One of these lines, resulting from a cross of separately transformed FAR- and PES lines (FARxPES) was shown to have an increased WE level compared to the wild-type. These results will now be a basis for further investigations on WE production in transgenic plants.