Abstract
Seed oil is important not only for human and animal nutrition, but also for various industrial applications. Numerous genetic engineering strategies have been attempted to increase the oil content per seed, but few of these strategies have involved manipulating the transporters. Pyruvate is a major source of carbon for de novo fatty acid biosynthesis in plastids, and the embryo's demand for pyruvate is reported to increase during active oil accumulation. In this study, we tested our hypothesis that oil biosynthesis could be boosted by increasing pyruvate flux into plastids. We expressed the known plastid-localized pyruvate transporter BILE ACID:SODIUM SYMPORTER FAMILY PROTEIN 2 (BASS2) under the control of a seed-specific soybean (Glycine max) glycinin-1 promoter in Arabidopsis thaliana. The resultant transgenic Arabidopsis plants (OEs), which expressed high levels of BASS2, produced seeds that were larger and heavier and contained 10–37% more oil than those of the wild type (WT), but were comparable to the WT seeds in terms of protein and carbohydrate contents. The total seed number did not differ significantly between the WT and OEs. Therefore, oil yield per plant was increased by 24–43% in the OE lines compared to WT. Taken together, our results demonstrate that seed-specific overexpression of the pyruvate transporter BASS2 promotes oil production in Arabidopsis seeds. Thus, manipulating the level of specific transporters is a feasible approach for increasing the seed oil content.
Highlights
Seed oil is an important source of energy, and is in increasing demand for various industrial applications (Dyer et al, 2008; Hayden et al, 2011)
We firstly examined whether seed-specific BILE ACID:SODIUM SYMPORTER FAMILY PROTEIN 2 (BASS2) overexpression increased the seed oil content by measuring the amount of total fatty acid methyl esters (FAMEs), which reflect changes in seed oil content, because >94% of fatty acids in seeds are stored in the form of TAG (Li et al, 2006)
We showed that the seed oil content was greater in the OE lines than in the wild type (WT) (Figure 3A, Table 1), but that the protein and carbohydrate contents of seeds were comparable among the OE and WT lines (Figures 5A,B)
Summary
Seed oil is an important source of energy, and is in increasing demand for various industrial applications (Dyer et al, 2008; Hayden et al, 2011). Overexpression of the transcription factor WRINKLED 1 (WRI1), which controls the expression of genes involved in lipid metabolism, including glycolysis and fatty acid biosynthesis, increased. An Arabidopsis mutant defective in both PPT and the plastid-localized enolase (ENO1) involved in glycolytic PEP provision exhibits retarded vegetative growth and defective flower development (Kubis et al, 2004). This double mutant exhibited frequent seed abortion and diminished oil amount in seeds, caused by disruption of multiple pathways including fatty acid synthesis
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