Researchers from the Solar Fuels Laboratory at the UW Centre of New Technologies, together with international collaborators, have revealed how Photosystem I (PSI) evolved to capture and direct solar energy without compromising performance.
Photosystem I (PSI) is a natural biophotocatalyst that converts sunlight into chemical energy with remarkably high quantum efficiency. Although PSI is essential to photosynthesis, the evolution of its energy-transfer pathways, from cyanobacteria through algae to land plants, has remained poorly understood.
Using ultralow-temperature two-dimensional electronic spectroscopy combined with advanced quantum dynamics modelling, the researchers investigated PSI from the extremophilic (volcanic) red microalga Cyanidioschyzon merolae. The results show that this biophotocatalyst contains two spatially distinct, low-energy “sinks”, sites toward which absorbed excitation energy is directed, located in both the PSI core (the domain for photoactivated charge separation and electron transfer) and its surrounding light harvesting antenna.
This organisation represents an evolutionary intermediate between cyanobacterial PSI, where excitation energy is directed predominantly toward the core, and plant PSI, where low-energy states are mainly associated with the antenna. The red algal system integrates elements of both architectures.
The study also demonstrates that the distribution of excitation energy between these sinks changes with temperature. Despite this redistribution, PSI maintains efficient energy trapping, enabling effective conversion of captured sunlight into chemical energy. These findings indicate that the evolutionary expansion of the light-harvesting antenna reshaped energy flow without compromising photosynthetic performance.
Beyond advancing the understanding of photosynthetic evolution, the discovery provides broader principles for designing efficient and resilient artificial light-harvesting systems. Distributing excitation energy across multiple, spatially separated pathways could help future solar-powered technologies combine high conversion efficiency with adaptability under changing environmental conditions.
The study was led by Prof. Joanna Kargul, with a significant contribution from Dr Miriam Izzo, at the Solar Fuels Laboratory, CeNT UW. It was conducted in collaboration with Prof. Hong-Guang Duan and Prof. Fulu Zheng and their teams at Ningbo University, Dr Ajay Jha and colleagues at the University of Oxford, and Prof. R. J. Dwayne Miller and his team at the University of Toronto.
Publication:
The article, “Excitonic Energy Transfer in Red Algal Photosystem I Reveals an Evolutionary Bridge between Cyanobacteria and Plants”, is published in the Proceedings of the National Academy of Sciences (PNAS).