Far-Red Light Absorbance

Most organisms that perform oxygenic photosynthesis do so by absorbing light in the visible region of the solar spectrum, from 400 to 700 nm. This is due to the absorbance characteristics of the pigments bound by their photosystems and associated antenna complexes. It has recently been discovered that certain cyanobacteria adapt to shaded environments where far-red light is enriched by expressing novel pigments that absorb far-red light. The fact that this is possible in cyanobacteria implies that other organisms that typically cannot use far-red light, which includes all our crops, could be engineered to do so. Because extending the absorbance cross section of a crop could lead to increased yields, it is of major interest to better understand the molecular bases of how some cyanobacteria use far-red light for photosynthesis.

So far, three ways of absorbing far-red light to drive cyanobacterial photosynthesis have been discovered. Our group studies those that are facultative, which means that they are capable of altering their pigment composition as a function of light wavelength availability. These are called far-red light photoacclimation (FaRLiP) and low light photoacclimation (LoLiP). In FaRLiP, some of the pigments bound to the photosystems are replaced by ones that can absorb far-red light. For example, in the still figure below, the sites of far-red light-absorbing chlorophyll f molecules are shown for Photosystem I from three cyanobacterial species. Additionally, a novel far-red light-absorbing peripheral antenna complex is expressed (top animation loop). In LoLiP, a novel phycobiliprotein complex is expressed that forms helical nanotubes and most likely binds to visible light-absorbing Photosystem I (bottom animation loop). In both cases, the Gisriel Lab is interested in leveraging these incredible features to gain insight into fundamental aspects of photosynthesis, and to use the natural design principles to engineer oxygenic phototrophs that typically cannot use far-red light.