Abstract
Pennycress (Thlaspi arvense L.) accumulates oil up to 35% of the total seed biomass, and its overall fatty acid composition is suitable for aviation fuel. However, for this plant to become economically viable, its oil production needs to be improved. In vivo culture conditions that resemble the development of pennycress embryos in planta were developed based on the composition of the liquid endosperm. Then, substrate uptake rates and biomass accumulation were measured from cultured pennycress embryos, revealing a biosynthetic efficiency of 93%, which is one of the highest in comparison with other oilseeds to date. Additionally, the ratio of carbon in oil to CO2 indicated that non-conventional pathways are likely to be responsible for such a high carbon conversion efficiency. To identify the reactions enabling this phenomenon, parallel labeling experiments with 13C-labeled substrates were conducted in pennycress embryos. The main findings of these labeling experiments include: (i) the occurrence of the oxidative reactions of the pentose phosphate pathway in the cytosol; (ii) the reversibility of isocitrate dehydrogenase; (iii) the operation of the plastidic NADP-dependent malic enzyme; and (iv) the refixation of CO2 by Rubisco. These reactions are key providers of carbon and reductant for fatty acid synthesis and elongation.
Highlights
Pennycress (Thlaspi arvense L.), a member of Brassicaceae family, is a winter annual that grows in temperate regions of North America (Hojilla-Evangelista et al, 2013)
In recent years, pennycress has been recognized as an oilseed crop that is suitable for jet fuel production due to its fatty acid (FA) composition (Vaughn et al, 2004; Moser et al, 2009)
Culture conditions are validated when the dry weight and the rates of biomass accumulation of cultured embryos are in agreement with those of in planta embryos.To establish the culture conditions that successfully resemble the in planta environment of the pennycress embryo, it was essential to characterize the composition of the liquid endosperm that naturally sustains the development of the embryo
Summary
Pennycress (Thlaspi arvense L.), a member of Brassicaceae family, is a winter annual that grows in temperate regions of North America (Hojilla-Evangelista et al, 2013). A recent life cycle assessment has further demonstrated that pennycress-derived fuels could qualify as advanced biofuel with >50% reductions in greenhouse gas emission compared with petroleum (Fan et al, 2013). These findings together highlight the potential of pennycress oil as an alternative source of jet fuel. In order to make pennycress an economically viable source of jet fuel, it is important to consider improving the current oil content (35% of the seed biomass) by metabolic engineering and/or breeding
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