Breaking the Red Limit: Efficient Trapping of Long-Wavelength Excitations in Chlorophyll-f-Containing Photosystem I

Because of its energetic requirements, oxygenic photosynthesis employs a particular chlorophyll, chlorophyll a, which only absorbs visible light up to 700 nm. This spectral restriction can be particularly limiting under the shade of a dense plant canopy, where the available light is highly enriched in far-red photons (700–800 nm). Therefore, a promising approach for increasing biomass yields is to push light-harvesting capacity beyond the natural spectral limits by introducing pigments absorbing at longer wavelengths than chlorophyll a. Interestingly, a group of cyanobacteria is capable of harvesting far-red light up to 800 nm by integrating the red-shifted chlorophyll f in their photosystems. Here, we clarify the molecular mechanisms allowing chlorophyll-f-containing photosystem I to collect and process such low-energy photons with surprisingly high efficiency, thus providing a starting point for optimizing the photosynthetic units of other organisms.