The fatty acid elongase of Physaria fendleri increases hydroxy fatty acid accumulation in transgenic Camelina

Abstract

Plant oils containing hydroxy fatty acids (HFA) are desirable for a wide variety of applications including lubricants, plasticizers, surfactants, polyesters, paints, sealants, biodiesel, and more. Due to unfavorable agronomic attributes of natural accumulators such as castor and lesquerella, many efforts have been made to produce hydroxyl fatty acids in crop plants. The hydroxy fatty acid synthesis pathway has been extensively studied and key genes such as the castor fatty acid hydroxylase, RcFAH, have been discovered. However, insertion of the RcFAH gene into various Arabidopsis backgrounds under the control of seed specific promoters failed to result in high accumulation of the desired HFA products, highlighting a need for more research to uncover additional constraints and factors affecting the fluxes involved with the accumulation of these unusual fatty acids in seed oil. In this study I investigated the effect of co-expressing a fatty acid elongase gene, LfKCS3, from Lesquerella (Physaria) fendleri along with the castor hydroxylase gene, RcFAH, on accumulation of hydroxyl fatty acids in seed oil of the crop plant Camelina sativa. On its own, wild type camelina contains no hydroxy fatty acids but insertion of the RcFAH gene results in accumulation of around 15% HFA in transgenic camelina, however, addition of the LfKCS3 gene resulted in a significant increase in very long chain 20-carbon hydroxyl fatty acids from <2% to 8%; total hydroxyl fatty acids also increased from 15% to 22% in the highest accumulating lines. The presence of the LfKCS3 enzyme effectively increased total HFA levels at all stages of oil accumulation in developing seeds while also decreasing the amount of these fatty acids left on the phospholipid, phosphatidylcholine. This combination of increased 20- carbon and total hydroxyl fatty acid accumulation along with the decreased HFA levels in phosphatidylcholine indicates that the LfKCS3 gene helps to enhance the flux of HFA out of phosphatidylcholine for incorporation of HFA into triacylglycerol, aiding in relief of the metabolic bottleneck for engineering economically viable levels of these fatty acids in oilseed crops.