Engineering the production of conjugated fatty acids in Arabidopsis thaliana leaves

Authors: Yurchenko, Olga; Shockey, Jay; GIDDA, SATINDER - University Of Guelph; SILVER, MAXWELL - University Of Guelph; CHAPMAN, KENT - University Of North Texas; MULLEN, ROBERT - University Of Guelph; Dyer, John

Submitted to: Plant Biotechnology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2017
Publication Date: 3/15/2017
Citation: Yurchenko, O., Shockey, J.M., Gidda, S.K., Silver, M.L., Chapman, K.D., Mullen, R.T., Dyer, J.M. 2017. Engineering the production of conjugated fatty acids in Arabidopsis thaliana leaves. Plant Biotechnology Journal. 15:1010-1023. doi: 10.111/pbi.12695.

Interpretive Summary: The fatty acid components of seed oils are chemically similar to the long-chain hydrocarbons of fossil oil, and, as such, represent outstanding potential sources of renewable fuel and feedstocks for industry. The demand for transport fuels and chemicals, however, is far greater than what agriculture can typically deliver. Thus, there is significant interest in developing novel approaches for producing higher amounts of energy-dense oils in crop plants. Production of oil in vegetative biomass, including leaves and stems, has emerged as an exciting and promising new approach for producing energy-dense oils in dedicated bioenergy crops. To expand the potential usage of the oil, scientists at the ARS lab in Maricopa, Arizona, in collaboration with scientists at the ARS lab in New Orleans, the University of North Texas, and the University of Guelph, tested whether the oil in leaves could be tailored for accumulation of conjugated fatty acids. These unusual fatty acids are easily oxidized and are important feedstocks for production of biobased plastics, and they also have potential usage as nutritional components of animal feed for increasing muscle leanness. Scientists first generated high-leaf-oil plant lines using the model plant Arabidopsis thaliana, then expressed several different genes for conjugated fatty acid synthesis and accumulation. The results identified a specific combination of two different genes that showed strong synergism in the elevation of leaf oil content, as well as accumulation of conjugated fatty acids. The results will provide a useful framework for scientists to produce other types of structurally diverse, industrially important fatty acids in plant leaves, thereby greatly increasing the number and types of high-value oils that can be produced in biomass crop plants.

Technical Abstract: The seeds of many non-domesticated plant species synthesize oils containing high amounts of a single unusual fatty acid, many of which have potential usage in industry. Despite the identification of enzymes for unusual oxidized fatty acid synthesis, the production of these fatty acids in engineered seeds remains low and is often hampered by their inefficient exclusion from phospholipids. Recent studies have established the feasibility of increasing triacylglycerol content in plant leaves, which provides a novel approach for increasing energy density of biomass crops. Here, we determined whether the fatty acid composition of leaf oil could be engineered to accumulate unusual fatty acids. Eleostearic acid (ESA) is a conjugated fatty acid produced in seeds of the tung tree (Vernicia fordii) and has both industrial and nutritional end-uses. Arabidopsis thaliana lines with elevated leaf oil were first generated by transforming wild-type, cgi-58 or pxa1 mutants (the latter two of which contain mutations disrupting fatty acid breakdown) with the diacylglycerol acyltransferases (DGAT1 and DGAT2) and/or oleosin genes from tung. High-leaf-oil plant lines were then transformed with tung FADX, which encodes the fatty acid desaturase/conjugase responsible for ESA synthesis. Analysis of lipids in leaves revealed that ESA was efficiently excluded from phospholipids, and co-expression of tung FADX and DGAT2 promoted a synergistic increase in leaf oil content and ESA accumulation. Taken together, these results provide a new approach for increasing leaf oil content that is coupled to accumulation of unusual fatty acids. Implications for production of biofuels, bioproducts, and plant-pest interactions are discussed.