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Metabolic Engineering of Soybean (Glycine max) and Camelina (Camelina sativa) for Improved Oil Functionality
Vegetable oils are important sources of food, feed and fuel. The value and usage can be enhanced by increased production of vitamin E and wax esters in the oil. To this end, this thesis explored the vitamin E and wax ester biosynthetic pathways in oil seed crops like soybean and camelina. Vitamin E consists of tocopherols, tocotrienols and provides oxidative stability to vegetable oils. Due to high antioxidant nature and limited occurence, production of tocotrienols in dicotyledonous oil seeds is expexted to improve oil functionality. Also, high alpha tocochromanols in vegetable oils enhances nutritional value. We generated soybean seeds with 6.5- to 7.1- fold increases in vitamin E, mainly through tocotrienols production by transgenic expression of barley homogentisate geranylgeranyl transferase (HGGT). Also, generated seeds with 5.4- and 16-fold increase in total vitamin E and alpha tocochromanols respectively by co-expressing soybean γ-tocopherol methyltransferase (γ-TMT/VTE4) with barley HGGT. Further, introgression of high vitamin E trait into stearidonic rich soybean had improved oxidative stability of oil. We also, addressed the limitation of homogentisate production for increased vitamin E, using metabolic engineering strategies in camelina. Seed specific expression of down regulated homogentisate oxygenase ( HGO) and de-regulated synthesis genes, Arabidopsis hydroxyphenylpyruvate dioxigenase (HPPD) and Eschericia coli bi-functional chorismate mutase/prephenate dehydrogenase (TyrA) alone or in combination resulted drastic increase in homogentisate with limited increase in vitamin E content. Where as, in presence of HGGT expression, tremendous increase in homogentisate and total vitamin E content suggests that homogentisate is not a limiting factor for vitamin E synthesis, except in lines expressing HGGT and HGGT/HGO RNAi where free HGA was not accumulated. Similarly, by exploring wax biosynthetic pathway we generated camelina lines producing novel wax esters with reduced chain length, mainly C42 and C44 consisting of C20 and C22 fatty acids and fatty alcohols, by co-expressing fatty acid reductase (FAR), wax synthase (WS) from jojoba with fatty acid elongase (FAE1) from carmbe. In summary, we conclude that enhanced vitamin E increaed the oxidative stability of polyunsaturated fatty acids and increased alpha forms improves nutritional value of soybean oil. Also, wax esters with reduced chain length improve stability and functionality.
Konda, Anji Reddy, "Metabolic Engineering of Soybean (Glycine max) and Camelina (Camelina sativa) for Improved Oil Functionality" (2016). ETD collection for University of Nebraska - Lincoln. AAI10143304.