Recent structural discoveries of photosystems I and II acclimated to absorb far-red light.

Photosystems I and II are the photooxidoreductases central to oxygenic photosynthesis and canonically absorb visible light (400–700 nm). Recent investigations have revealed that certain cyanobacteria can acclimate to environments enriched in far-red light (700–800 nm), yet can still perform oxygenic photosynthesis in a process called far-red light photoacclimation, or FaRLiP. During this process, the photosystem subunits and pigment compositions are altered. Here, the current structural understanding of the photosystems expressed during FaRLiP is described. The design principles may be useful for guiding efforts to engineer shade tolerance in organisms that typically cannot utilize far-red light. • Some cyanobacteria acclimate to environments enriched in far-red light. • During this process, the photosystems are altered to absorb far-red light. • Cryo-EM has revealed the structures of the far-red light-absorbing photosystems. • Identifying sites that bind red-shifted chlorophylls required novel approaches. • The structures provide design principles to confer far-red light absorbance. [ABSTRACT FROM AUTHOR]