Abstract
Flax (Linum usitatissinum L.) oil is an important source of α-linolenic (C18:3 ω-3). This polyunsaturated fatty acid is well known for its nutritional role in human and animal diets. Understanding storage lipid biosynthesis in developing flax embryos can lead to an increase in seed yield via marker-assisted selection. While a tremendous amount of work has been done on different plant species to highlight their metabolism during embryo development, a comprehensive analysis of metabolic flux in flax is still lacking. In this context, we have utilized in vitro cultured developing embryos of flax and determined net fluxes by performing three complementary parallel labeling experiments with 13C-labeled glucose and glutamine. Metabolic fluxes were estimated by computer-aided modeling of the central metabolic network including 11 cofactors of 118 reactions of the central metabolism and 12 pseudo-fluxes. A focus on lipid storage biosynthesis and the associated pathways was done in comparison with rapeseed, arabidopsis, maize and sunflower embryos. In our hands, glucose was determined to be the main source of carbon in flax embryos, leading to the conversion of phosphoenolpyruvate to pyruvate. The oxidative pentose phosphate pathway (OPPP) was identified as the producer of NADPH for fatty acid biosynthesis. Overall, the use of 13C-metabolic flux analysis provided new insights into the flax embryo metabolic processes involved in storage lipid biosynthesis. The elucidation of the metabolic network of this important crop plant reinforces the relevance of the application of this technique to the analysis of complex plant metabolic systems.
Highlights
During the last decades the production and consumption of plant oil-derived products has steadily increased worldwide at a rate of roughly 5% per year [1]
We have identified the major route of intracellular carbon with 13C metabolic flux analysis (13C-MFA) in developing flax embryos
Three distinct phases of lipid accumulation were identified during flax embryo development based on differences in the linear velocities of lipid accumulation
Summary
During the last decades the production and consumption of plant oil-derived products has steadily increased worldwide at a rate of roughly 5% per year [1]. Unsaturated fatty acids, e.g., oleic (18:1) and linoleic (18:2) acids [6,7] are well represented in soybean, rapeseed and sunflower The consumption of these different oils has many repercussions on human health [8,9]. Sucrose is enzymatically hydrolyzed to fructose and glucose These hexoses and hexose-phosphate derivatives enter the glycolytic and the oxidative-pentose pathways to generate acetyl-CoA and reduce equivalents. Its glycolytic precursors are either generated within plastids or imported from the cytosol through the action of dedicated, yet to be identified transporters [20] Because of this dual location, the predominant source of carbon for plastidial acetyl-CoA originates from one of the two glycolytic pathways. The recognition of similarities and differences between diverse oilseeds sheds light on the participation of the different carbon fluxes, from sucrose to fatty acids, during the active period of lipid biosynthesis and accumulation of storage lipids in developing oilseeds
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