Epsilon Open Archive

Abstract

World chemical and energy supplies for industry are today highly dependent on unsustainable fossil reserves. Vegetable lipids with similar chemical structures to fossil oil could be the ultimate renewable solution to replace fossil oil and provide environmentally friendly feedstocks and energy resources. Wax esters and triacylglycerols (TAG) are two groups of lipid with applications in industry as lubricants, surfactants and biodiesel. However, global production of wax esters and TAG is limited to a few crop species such as jojoba, carnauba, oil palm, soybean and rapeseed. Further, there are restrictions on arable land for oilseed crop growth, and the demand for vegetable lipids is predicted to increase in coming decades. Therefore, there is an urgent need to establish sustainable technologies and develop new alternative oil crop species to meet an expected future vegetable lipid demand.

This thesis examined the potential for production of wax esters and TAG with different qualities in tobacco (Nicotiana benthamiana) leaves, and in rice (Oryza sativa) endosperm by metabolic engineering. In tobacco leaves, a new metabolic pathway was introduced into chloroplasts by combining bacterial- and plant-derived genes (AtFAR6, AtPES2, MaFAR, MhWS, tpMaFAR::MhWS, AtWRI1) for wax ester biosynthesis. Combinations of the gene functions resulted in production of wax esters with differing composition to a level of 0.9% of leaf dry weight (DW). The newly introduced pathway was further engineered by RNAi inhibition of the KASII gene. Additional co-expression of KASIIRNAi constructs resulted in increased palmitic/stearic acid ratio, which significantly improved wax ester production in AtFAR6-containing combinations. The novel gene fusion tpMaFAR::MhWS was further investigated by stable transformation of tobacco plants. Wax ester content in transformants was increased eight-fold compared with wild-type (WT). In rice, overexpression of both full-length and truncated Arabidopsis transcription factor AtWRI1 in endosperm tissues resulted respectively in sevenfold and four-fold accumulation of TAG content compared with WT. Taken together, these results showed that valuable oleochemicals could be increased considerably in plants.