Multiple routes to red-shifted chlorophyll d-based photosynthesis

Mehra, H. S.; Magdaong, N. C. M.; Flesher, D. A.; Shen, G.; Ulrich, N. J.; Brininger, C. M.; Niedzwiedzki, D. M.; Miller, S. R.; Gisriel, C. J.

doi:10.64898/2026.06.16.732656

bioRxiv · 10.64898/2026.06.16.732656

Multiple routes to red-shifted chlorophyll d-based photosynthesis

Mehra, H. S.·Magdaong, N. C. M.·Flesher, D. A.·Shen, G.·Ulrich, N. J.·Brininger, C. M.·Niedzwiedzki, D. M.·Miller, S. R.·Gisriel, C. J.

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Abstract

Strains of the cyanobacterium Acaryochloris marina exhibit diverse far-red light-harvesting properties during chlorophyll d-based photosynthesis. Here, we show that differences in light absorption among A. marina strains arise exclusively from Photosystem I (PSI) and reflect variation in multiple low-energy chlorophyll states. Time-resolved fluorescence reveals different combinations of low-energy states among strains, generating a continuum of spectral phenotypes. Cryo-EM structures of PSI at [~]1.8 [A] resolution reveal similar low-energy states arising from distinct pigment environments, demonstrating that red-shifted absorption is not governed by a single conserved motif. Phylogenetic analyses show that spectral tuning evolved through modular variation and reassortment of PSI components. These results indicate that distinct pigment configurations can converge on similar low-energy states, extending light harvesting near the energetic limit of oxygenic photosynthesis.

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Mehra, H. S., Magdaong, N. C. M., Flesher, D. A., Shen, G., Ulrich, N. J., Brininger, C. M., Niedzwiedzki, D. M., Miller, S. R., Gisriel, C. J.. 2026-06-20. Multiple routes to red-shifted chlorophyll d-based photosynthesis. https://doi.org/10.64898/2026.06.16.732656

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