Strong heterologous electron sink outcompetes alternative electron transport pathways in photosynthesis
: Hubáček, Michal; Wey, Laura T.; Kourist, Robert; Malihan-Yap, Lenny; Nikkanen, Lauri; Allahverdiyeva, Yagut
Publisher: John-Wiley & Sons
: 2024
: Plant Journal
: The Plant journal : for cell and molecular biology
: Plant J
: 119
: 5
: 2500
: 2513
: 0960-7412
: 1365-313X
DOI: https://doi.org/10.1111/tpj.16935
: https://onlinelibrary.wiley.com/doi/10.1111/tpj.16935
: https://research.utu.fi/converis/portal/detail/Publication/457244021
Improvement of photosynthesis requires a thorough understanding of electron partitioning under both natural and strong electron sink conditions. We applied a wide array of state-of-the-art biophysical and biochemical techniques to thoroughly investigate the fate of photosynthetic electrons in the engineered cyanobacterium Synechocystis sp. PCC 6803, a blueprint for photosynthetic biotechnology, expressing the heterologous gene for ene-reductase, YqjM. This recombinant enzyme catalyses the reduction of an exogenously added substrate into the desired product by utilising photosynthetically produced NAD(P)H, enabling whole-cell biotransformation. Through coupling the biotransformation reaction with biophysical measurements, we demonstrated that the strong artificial electron sink, outcompetes the natural electron valves, the flavodiiron protein-driven Mehler-like reaction and cyclic electron transport. These results show that ferredoxin-NAD(P)H-oxidoreductase is the preferred route for delivering photosynthetic electrons from reduced ferredoxin and the cellular NADPH/NADP+ ratio as a key factor in orchestrating photosynthetic electron flux. These insights are crucial for understanding molecular mechanisms of photosynthetic electron transport and harnessing photosynthesis for sustainable bioproduction by engineering the cellular source/sink balance. Furthermore, we conclude that identifying the bioenergetic bottleneck of a heterologous electron sink is a crucial prerequisite for targeted engineering of photosynthetic biotransformation platforms.
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This work was supported by the Academy of Finland (AlgaLEAF, project no. 322754, to YA; Revisiting Photosynthesis, project no. 315119, to YA), the Novo Nordisk Foundation (PhotoCat, project no. NNF20OC0064371, to YA) and the EU FET Open project FuturoLEAF (grant agreement No. 899576, to YA).
