Photoautotrophs are organisms that use light energy and inorganic carbon to produce organic materials. Eukaryotic photoautotrophs absorb energy through the chlorophyll molecules in their chloroplasts while prokaryotic photoautotrophs use chlorophylls and bacteriochlorophylls present in their cytoplasm. All known photoautotrophs perform photosynthesis. Examples include plants, algae, and cyanobacteria.
Origin and the Great Oxidation Event
Chemical and geological evidence indicate that photosynthetic cyanobacteria existed about 2.6 billion years ago and anoxygenic photosynthesis had been taking place since a billion years before that. Oxygenic photosynthesis was the primary source of oxygenation and led to the Great Oxidation Event (the Oxygen Catastrophe) roughly 2.4 to 2.1 billion years ago. Although the end of the Great Oxidation Event was marked by a significant decrease in gross primary productivity that eclipsed extinction events, the development of aerobic respiration enabled energy extraction from organic molecules, allowing multi-cellular growth and diversification of life on Earth.
Cyanobacteria is the only prokaryotic group that performs oxygenic photosynthesis. Anoxygenic photosynthetic bacteria use PSI- and PSII-like photosystems, which are pigment protein complexes for capturing light. Both of these photosystems use bacteriochlorophyll. There are multiple hypotheses for how oxygenic photosynthesis evolved. The loss hypothesis states that PSI and PSII were present in anoxygenic ancestor cyanobacteria from which the different branches of anoxygenic bacteria evolved. The fusion hypothesis states that the photosystems merged later through horizontal gene transfer. The most recent hypothesis suggests that PSI and PSII diverged from an unknown common ancestor with a protein complex that was coded by one gene. These photosystems then specialized into the ones that are found today.
Eukaryotic photoautotrophs include red algae, haptophytes, stramenopiles, cryptophytes, chlorophytes, and land plants. These organisms perform photosynthesis through organelles called chloroplasts and are believed to have originated about 2 billion years ago. Comparing the genes of chloroplast and cyanobacteria strongly suggests that chloroplasts evolved as a result of endosymbiosis with cyanobacteria that gradually lost the genes required to be free-living. However, it is difficult to determine whether all chloroplasts originated from a single, primary endosymbiotic event, or multiple independent events.
- Olson, John M.; Blankenship, Robert E. (2004). "Thinking About the Evolution of Photosynthesis". Photosynthesis Research. 80 (1–3): 373–386. doi:10.1023/B:PRES.0000030457.06495.83. ISSN 0166-8595. PMID 16328834. S2CID 1720483.
- Hodgskiss, Malcolm S. W.; Crockford, Peter W.; Peng, Yongbo; Wing, Boswell A.; Horner, Tristan J. (2019-08-27). "A productivity collapse to end Earth's Great Oxidation". Proceedings of the National Academy of Sciences. 116 (35): 17207–17212. doi:10.1073/pnas.1900325116. ISSN 0027-8424. PMC 6717284. PMID 31405980.
- Lyons, Timothy W.; Reinhard, Christopher T.; Planavsky, Noah J. (February 2014). "The rise of oxygen in Earth's early ocean and atmosphere". Nature. 506 (7488): 307–315. doi:10.1038/nature13068. ISSN 0028-0836. PMID 24553238. S2CID 4443958.
- Sánchez‐Baracaldo, Patricia; Cardona, Tanai (February 2020). "On the origin of oxygenic photosynthesis and Cyanobacteria". New Phytologist. 225 (4): 1440–1446. doi:10.1111/nph.16249. ISSN 0028-646X. PMID 31598981.
- Björn, Lars (June 2009). "The evolution of photosynthesis and chloroplasts". Current Science. 96 (11): 1466–1474.
- Yoon, Hwan Su; Hackett, Jeremiah D.; Ciniglia, Claudia; Pinto, Gabriele; Bhattacharya, Debashish (May 2004). "A Molecular Timeline for the Origin of Photosynthetic Eukaryotes". Molecular Biology and Evolution. 21 (5): 809–818. doi:10.1093/molbev/msh075. ISSN 1537-1719. PMID 14963099.