Mechanistic Modeling of Electron Transport Identifies Directions for Sustainable Improvement of Photosynthesis

The Science

Evolution selects plant species for reproduction and survivability. The electron transport chain (ETC) between the two photosystems of photosynthesis (PSI and PSII) in chloroplast thylakoid membranes appears to be suboptimal for photosynthesis due to evolutionary constraints.

Photochemical models of photosynthetic electron transport were developed to determine how the structure of the ETC and thylakoid controls the oxidation-reduction (redox) reactions between key protein complexes and electron carriers and therefore the maximal electron transport rate. Models were validated for species across diverse environments and C₃ and C₄ photosynthetic pathways.

Models show the electron transport capacity can be increased while the risk of photooxidative damage can be simultaneously minimized by increasing the abundances of reaction centers, cytochrome b₆f complexes, and mobile electron carriers. The new modeling results describe previously unexplained experimental findings regarding the physiological impacts of the abundances of ETC components on plant productivity.

The Impact

Genetically improving photosynthesis is a key strategy to boosting crop production to meet the rising demand for food and fuel and for carbon sequestration. The models developed and the insights generated facilitate the development of sustainable photosynthetic systems for greater crop yields and carbon sequestration potentials.

Summary

Genetically improving photosynthesis is a key strategy to boosting crop production to meet the rising demand for food and fuel by a rapidly growing global population in a warming climate. Many components of the photosynthetic apparatus have been targeted for genetic modification for improving photosynthesis. Successful translation of these modifications into increased plant productivity in fluctuating environments will depend on whether the ETC can support the increased electron transport rate without risking overreduction and photodamage. At present atmospheric conditions, the ETC appears suboptimal and will likely need to be modified to support proposed photosynthetic improvements and to maintain energy balance. This study derives photochemical equations to quantify the transport capacity and the corresponding reduction level based on the kinetics of redox reactions along the ETC. Using these theoretical equations and measurements from diverse C₃/C₄ species across environments, the researcher identified several strategies that can simultaneously increase the transport capacity and decrease the reduction level of the ETC. These strategies include increasing the abundance of reaction centers, cytochrome b₆f complexes, and mobile electron carriers; improving their redox kinetics; and decreasing the fraction of secondary quinone–nonreducing PSII reaction centers. This research also shed light on several previously unexplained experimental findings regarding the physiological impacts of the abundances of the cytochrome b₆f complex and plastoquinone. The model developed and the insights generated from it facilitate the development of sustainable photosynthetic systems for greater crop yields.

Principal Investigator

Lianhong Gu
Oak Ridge National Laboratory
[email protected]

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research is supported by the Biological and Environmental Research program within the U.S. Department of Energy’s (DOE) Office of Science via Oak Ridge National Laboratory (ORNL) Terrestrial Ecosystem Science (TES) Scientific Focus Area (SFA). ORNL is managed by UT-Battelle, LLC, for DOE under contract DE-AC05-00OR22725.

References