Researchers at Ludwig-Maximilians-Universität Munich (LMU), led by Professor Dario Leister, have demonstrated for the first time that oxygenic photosynthesis is possible with only a single photosystem. The findings, published in Nature Communications, challenge one of the fundamental paradigms of biology.
Until now, it was considered established that oxygenic photosynthesis requires the interaction of two protein complexes – Photosystem II and Photosystem I. This principle has been part of core biological knowledge for more than 50 years. The new findings show that this assumption is apparently not universal.
"When a textbook paradigm falls, it affects more than just one detail of our knowledge – it changes our view of a fundamental biological process," says Professor Dario Leister, Chair of Plant Molecular Biology at LMU and lead author of the study. "Our results show that nature is much more flexible than we previously assumed."
The project originally pursued a different objective: the researchers aimed to introduce a plant Photosystem I into the cyanobacterium Synechocystis. Using genetic engineering and adaptive laboratory evolution, they unexpectedly generated organisms that completely lack Photosystem I.
"We were actually trying to achieve something entirely different," says Leister. "That this would result in organisms capable of growing, fixing carbon dioxide, and producing oxygen without Photosystem I was completely unexpected."
The team also identified the mechanism that enables the cyanobacteria to compensate for the missing photosystem. Several evolutionary adaptations reorganize the photosynthetic electron transport chain. A particularly strong proton gradient allows the NDH-1 complex to operate in reverse, producing the reducing agent NADPH – a function previously thought to be carried out exclusively by Photosystem I.
The discovery opens new perspectives on the evolution of photosynthesis and could ultimately provide new approaches for developing more efficient photosynthetic systems and biotechnological applications.