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Thinking about the evolution of photosynthesis.
John M Olson1, Robert E Blankenship
1Department of Biochemistry and Molecular Biology, Lederle Graduate Research Center, University of Massachusetts, Amherst, MA, 01003-4505, USA.
Photosynthesis Research
|December 6, 2005
Summary
Photosynthesis evolved early, with ancient bacteria predating cyanobacteria. The photosynthetic apparatus is a mosaic, with reaction centers and antenna complexes having independent evolutionary histories.
Area of Science:
- Biochemistry
- Evolutionary Biology
- Microbiology
Background:
- Photosynthesis is an ancient biological process, with evidence suggesting cyanobacteria existed 2.5-2.6 billion years ago, preceded by anoxygenic photosynthetic bacteria.
- Carbon isotope data indicate autotrophic carbon fixation occurred at least a billion years earlier, but the earliest photosynthetic organisms remain poorly understood.
- The photosynthetic apparatus comprises reaction centers, antenna complexes, electron transfer complexes, and carbon fixation machinery, each with potentially distinct evolutionary paths.
Purpose of the Study:
- To explore the evolutionary origins and diversification of photosynthetic reaction centers and apparatus.
- To present and contrast two models for the evolution of reaction centers in various photosynthetic bacteria.
- To elucidate the transition from anoxygenic to oxygenic photosynthesis.
Main Methods:
- Comparative analysis of evolutionary histories of photosynthetic apparatus components.
- Review of existing hypotheses and models for reaction center evolution (selective loss and fusion models).
- Interpretation of fossil and geochemical evidence (carbon isotopes, chemical evidence).
Main Results:
- The photosynthetic apparatus is viewed as a mosaic of substructures with independent evolutionary histories.
- Two models, selective loss and fusion, are proposed for the evolution of reaction centers (RC1 and RC2) in different bacterial lineages.
- Cyanobacteria possess both RC1 and RC2, potentially from a genetic fusion event, while other bacteria lost one type.
- Antenna/light-harvesting complexes show independent evolutionary trajectories.
- The transition to oxygenic photosynthesis involved cyanobacteria utilizing water as an electron donor, possibly preceded by hydrogen peroxide and ferrous iron.
Conclusions:
- The evolution of photosynthesis is complex, involving the assembly of components with diverse origins.
- Understanding the mosaic nature of the photosynthetic apparatus is key to deciphering its early evolution.
- The development of oxygenic photosynthesis by cyanobacteria marked a significant evolutionary transition, enabled by the use of water as an electron donor.