Location: Plant Genetics ResearchTitle: Metabolic flux analysis of the non-transitory starch tradeoff for lipid production in mature tobacco leaves
|CHU, KEVIN - Washington State University
|KOLEY, SOMNATH - Danforth Plant Science Center
|JENKINS, LAUREN - Danforth Plant Science Center
|KAMBHAMPATI, SHRIKAAR - Danforth Plant Science Center
|FOLEY, KEVIN - Danforth Plant Science Center
|ARP, JENNIFER - Danforth Plant Science Center
|CZYMMEK, KIRK - Danforth Plant Science Center
|BATES, PHILIP - Danforth Plant Science Center
|Allen, Douglas - Doug
Submitted to: Metabolic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2021
Publication Date: 1/1/2022
Citation: Chu, K.L., Koley, S., Jenkins, L.M., Bailey, S.R., Kambhampati, S., Foley, K., Arp, J.J., Morley, S.A., Czymmek, K., Bates, P.D., Allen, D.K. 2022. Metabolic flux analysis of the non-transitory starch tradeoff for lipid production in mature tobacco leaves. Metabolic Engineering. 69:231-248. https://doi.org/10.1016/j.ymben.2021.12.003.
Interpretive Summary: Lipids are the most energy dense storage reserve in biomass, with over twice the energy content per gram than carbohydrates. Thus, lipids are an excellent alternative to petroleum for fuels and other feed stocks. The demand for lipids is expected to double by 2050, therefore crops with enhanced production of lipids are sorely needed. Tobacco lines that have been engineered to produce 30% of leaf biomass as lipid, were studied to understand the underlying changes in metabolism necessary to accommodate the increased lipid accumulation. We discovered that tobacco leaves store significant amounts of starch over development. The starch is dramatically reduced in the lipid producing lines. Thus, there is a trade off between starch and lipid in the leaves. The studies highlight the adjustments in metabolism necessary to accommodate the trade off and describe how leaves can serve as a valuable source of lipids for renewable needs.
Technical Abstract: The metabolic plasticity of tobacco leaves has been demonstrated via the generation of transgenic plants that can accumulate over 30% dry weight as triacylglycerols. In investigating the changes in carbon partitioning in these high lipid-producing (HLP) leaves, foliar lipids accumulated stepwise over development. Interestingly, non-transient starch was observed to accumulate with plant age in WT but not HLP leaves, with a drop in foliar starch concurrent with an increase in lipid content. The metabolic carbon tradeoff between starch and lipid was studied using 13CO2-labeling experiments and isotopically nonstationary metabolic flux analysis, not previously applied to the mature leaves of a crop. Fatty acid synthesis was investigated through assessment of acyl-acyl carrier proteins using a recently derived quantification method that was extended to accommodate isotopic labeling. Analysis of labeling patterns and flux modeling indicated the continued production of unlabeled starch, sucrose cycling, and a significant contribution of NADP-malic enzyme to plastidic pyruvate production for the production of lipids in HLP leaves, with the latter verified by enzyme activity assays. The results suggest an inherent capacity for a developmentally regulated carbon sink in tobacco leaves and may in part explain the uniquely successful leaf lipid engineering efforts in this crop.