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Lipid flippases in plants play critical roles in vegetative growth and development & Improving the emerging biodiesel feedstock Camelina sativa using a transgenic approach
AdvisorHarper, Jeffrey F.
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The following dissertation divides into two major topics. The first set of studies (Chapters 1 and 2) investigate the importance of P4-type ATPases (i.e., lipid flippases) for vegetative growth in Arabidopsis (Arabidopsis thaliana). The second set of studies (Chapter 3) includes various attempts to improve the yield output and value of Camelina (Camelina sativa), an emerging biofuel feedstock, using a transgenic approach. Lipid flippases consume ATP to facilitate the transport of specific lipids across the membrane bilayer, depositing lipid substrates on cytosolic facing surfaces. In plants, flippases are called AminophosphoLipid ATPases (ALAs). There are twelve ALAs in Arabidopsis that divide into five phylogenetic clusters conserved in angiosperms. To further study their importance for vegetative growth and development, T-DNA insertion mutants were obtained for the two most abundantly expressed cluster-3 ALAs in vegetative tissues (ALA4 and ALA5). The first study (chapter 1) describes double mutants deficient in ALA4 and ALA5, which were shown to have severely reduced growth in roots, rosettes, and bolts. ala4/5 double mutants also displayed perturbations in the concentrations of glycosphingolipids, which are critical for plant growth. The second study (chapter 2) describes a potential role for ALA4/5 in sphingolipid metabolism, where ALA4/5 and other ALAs flip glucosylceramide (GlcCer) sphingolipids across the membrane bilayer for catabolism in the cytosol, with ala4/5 mutants being deficient in this process and accumulating GlcCers to levels that potentially inhibit growth. The third study (chapter 3) details various attempts to improve the emerging biofuel feedstock Camelina (Camelina sativa) using a transgenic approach. Transgenes were introduced into Camelina in an attempt to convey the following traits: resistance to the herbicide glyphosate, increased seed yield, improved drought tolerance, and modification to seed oil profile for improved biodiesel performance. While some of these transgenic modifications appeared to be successful in imbuing their desired traits, further research will be required to validate their efficacy in field conditions.