Sugar Potentiation of Fatty Acid and Triacylglycerol Accumulation.

Photosynthetically derived sugar provides carbon skeletons for lipid biosynthesis. We used mutants of Arabidopsis () and the expression of oleogenic factors to investigate relationships among sugar availability, lipid synthesis, and the accumulation of triacylglycerol (TAG) in leaf tissue. The mutation disables the small subunit of ADP-glucose pyrophosphorylase, the first step in starch synthesis, and the mutation disables a sucrose/proton symporter that facilitates sucrose loading from leaves into phloem. The double mutant increases glucose plus sucrose content in leaves 80-fold relative to the wild type, total fatty acid (FA) content 1.8-fold to 8.3% dry weight, and TAG more than 10-fold to 1.2% dry weight. The WRINKLED1 transcription factor also accumulates to higher levels in these leaves, and the rate of FA synthesis increases by 58%. Adding , which disables chalcone synthase, had little effect, but adding the mutation, which disables an importer of lipids into plastids to create , increased total leaf FA to 13.5% dry weight and TAG to 3.8% dry weight, demonstrating a synergistic effect upon combining these mutations. Combining with the mutation, deficient in the predominant TAG lipase, had little effect on total FA content but increased the TAG accumulation by 66% to 2% dry weight. Expression of the transcription factor, along with and the oil body-associated protein, in the mutant doubled leaf FA content and increased TAG content to 2.3% dry weight, a level 4.6-fold higher than that resulting from expression of the same factors in the wild type.