A collaborative study led by Christopher Gisriel at Yale University and Tanai Cardona at Queen Mary University of London offers new insight on the origin and evolution of a unique type of photosynthesis that enables some bacteria, specifically cyano­bacteria, to harness far-red light. Far-red light, which falls between 700 to 800 nanometers, is beyond the range typically used for photo­synthesis because it contains lower energy than the standard visible range between blue and red. The study's insights into cyano­bacteria's ability to use far-red light are crucial, as they could provide conceptual frameworks to engineer enhanced plants with expanded light absorption capa­bilities for appli­cations in biotech and agri­culture. 

The study's findings not only shed light on the evolutionary journey of far-red photo­synthesis but also hold profound impli­cations for our understanding of life in the cosmos. M-dwarf stars, the most common type of star in the universe, emit far more far-red light than visible light, making them potential havens for far-red photosynthesis. If life can thrive on planets orbiting these stars, it could expand the boundaries of our search for extra­terrestrial life. 

The researchers' analysis indicates that the ability to use far-red light evolved in two distinct stages. An early stage that involved cyano­bacteria innovating a new pigment, chloro­phyll f, enabling the photosystem to harvest far-red light for the first time. In addition, they developed a modified photosystem that could use this pigment to power the oxygen release reaction using only the lower energy red light. This stage possibly occurred in ancestral cyano­bacteria forms and might have started as early as 3 billion years ago​​. 

The late stage, occurring approxi­mately 2 billion years ago, further optimized the capacity to harvest far-red light by evolving a second modified photosystem incorporating chlorophyll f at critical locations. This phase coincided with the diversification of cyanobacteria into the lineages existing today. Signi­ficantly, the study also found evidence suggesting that far-red light photo­synthesis can be gained by a cyano­bacterium through horizontal gene transfer. This discovery indicates that the complex trait could be introduced viably into a photo­synthetic organism not previously adapted to use far-red light.

The research underscores the intricate and adaptive nature of photo­synthetic systems and opens new horizons for understanding how organisms evolve to harness energy efficiently in varying environ­mental conditions. The study also lays the groundwork for future explorations into optimising light use in biotech and agriculture, which could lead to algae strains or crop improvements in less-than-ideal light conditions. (Source: QMUL)

Reference: C. J. Gisriel et al.: Molecular diversity and evolution of far-red light-acclimated photosystem I, Front. Plant Sci., online 20 November 2023; DOI: 10.3389/fpls.2023.1289199

Link: School of Biological and Behavioural Sciences, Queen Mary University of London, London, UK