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Increasing photosynthetic efficiency of energycane under fluctuating lights

Moonsub Lee, Fredy Altpeter, Donald Ort


Engineering bioenergy crops to produce natural oils provides an alternative energy source that can
help ensure energy security while mitigating environmental problems associated with traditional
fossil fuels. The C4 photosynthetic pathway of bioenergy grasses such as sugarcane, while the most
efficient pathway, needs to be improved in order to accommodate the high energetic costs of oil
biosynthesis without decreasing plant growth. Crop canopy modeling demonstrates that the rapidly
changing light environment experienced by bioenergy crops in dense plantings limits photosynthetic
efficiency. However, there has been little empirical research investigating the impact of rapidly
changing light environments on C 4 bioenergy crops biomass production or on developing
engineering strategies to improve the efficiency of bioenergy grasses in dynamic light environments.
Previous modeling of C 4 photosynthesis in fluctuating light environments suggested that
photosynthetic efficiency is reliant on the coordination of the C 4 and C 3 metabolic cycles. We
hypothesize that large metabolite pools act as buffers to minimize changes to metabolite fluxes in
rapid changes in light environments, and that this buffering helps maintain coordination of the C 4
and C 3 metabolic cycles. Increased chloroplast volume would increase this metabolite buffering capacity by increasing metabolite pool sizes, and thereby enhance the C4 photosynthetic efficiency
in fluctuating light conditions. We are engineering increased sugarcane chloroplast volume by
genetically manipulating various components of the chloroplast division machinery. We have
already developed a methodology for estimating chloroplast volume of sugarcane leaves using
confocal microscopy and a 3-D image program. Leaf microscopy, leaf photosynthetic gas exchange,
and above ground biomass production in greenhouse trials will be used to select the best chloroplast
modifications for future field trails.

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The Ort Lab is supported by many public and private partnerships, including the Bill & Melinda Gates Foundation, the Foundation for Food and Agriculture Research, the UK Government's Department for International Development, the U.S. Department of Energy, and the Advanced Research Projects Agency-Energy.

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