Rewiring photosynthesis with synthetic biology

Photosynthesis is the pivotal biological reaction on the planet, providing the food we eat and the oxygen we breathe, and removing CO2 from the atmosphere. Photosynthesis consists of two reactions: the light reactions absorb light energy from the sun and use this to split water (H2O) into electrons, protons and oxygen, and the dark reactions use the electrons and protons from the light reactions to 'fix' CO2 from the atmosphere into simple sugars that are the basis of the food chain. Importantly, the light reactions have a much higher capacity than the dark reactions, resulting in much of the absorbed light energy being dissipated rather than being used to 'fix' CO2. In this proposal we will use synthetic-biology methods to engineer an additional enzyme (a cytochrome P450, CYP) in-between the light reactions and the dark reactions. This will 'rewire' photosynthesis such that more absorbed light is used to power useful chemical reactions. This work therefore represents an innovation whereby a range of additional valuable chemical reactions can be powered by the sun in cyanobacteria and plants. We have previously developed a 'platform' cyanobacterial cell line where the 'wasted' electrons of photosynthesis are rewired (using a CYP) to degrade the pollutant atrazine (a herbicide used in agriculture). Atrazine while banned in the EU is still one of the most prevalent pesticides in some groundwater systems. This cell line may be used in the efficient bioremediation of such polluted wastewater areas. In this proposal we aim to further develop the use of CYP in rewiring photosynthesis such that we can improve and regulate the yield of the desired products, as well as enhance the diversity of products that can be powered by light. Further, we will fully characterise the physiology of engineered cell lines such that we can interrogate the fundamental mechanism of this photosynthetic electron transfer. In addition, we aim to transfer this technology to the model higher plant Arabidopsis as a first step in improving photosynthetic potential in crop species. The 'added value' we aim to introduce into cyanobacteria and plants may be a critical step toward the commercial realisation of using photosynthetic species to generate 'biofuels' that may one day replace our current dependence on fossil fuels.