Abstract
Photosynthesis is a biochemical process essential for life, serving as the ultimate source of chemical energy for phototrophic and heterotrophic life forms. Since the machinery of the photosynthetic electron transport chain is quite complex and is unlikely to have evolved multiple independent times, it is believed that this machinery has been transferred to diverse eukaryotic organisms by endosymbiotic events involving a eukaryotic host and a phototrophic endosymbiont. Thus, photoautotrophy, as a benefit, is transmitted through the evolution of plastids. However, many eukaryotes became secondarily heterotrophic, reverting to hetero-osmotrophy, phagotrophy, or parasitism. Here, I briefly review the constructive evolution of plastid endosymbioses and the consequential switch to reductive evolution involving losses of photosynthesis and plastids and the evolution of parasitism from a photosynthetic ancestor.
Highlights
Phototrophic organisms are the foundation of every food chain on Earth
The evolution of phototrophic eukaryotes was enabled by endosymbioses between a eukaryotic host and a prokaryotic or eukaryotic endosymbiont
Since the main benefit of photoautotrophy is not essential for the survival of cells that have kept their ancestral mechanisms of heterotrophy, frequent losses of photosynthesis are found throughout the diversity of eukaryotic phototrophs
Summary
Phototrophic organisms are the foundation of every food chain on Earth. We all depend on the ability of tiny bacteria to photosynthesize, using the energy from sunlight for the conversion of CO2 and water into organic compounds. Since cyanobacteria were more or less limited to the aquatic environment, they entered into a mutualistic relationship with a heterotrophic eukaryotic cell in an endosymbiotic event dated about one billion years ago [2] This led to the evolution of symbiotic entities in primarily phototrophic eukaryotes deeply integrated into the host cell in the form of eukaryotic organelles called plastids. Photosynthesis transforms the energy of sunlight into fuel for heterotrophic life forms through the production of energetically rich organic carbon-containing molecules (sugars), with their subsequent decomposition by glycolysis and oxidative phosphorylation This biotrophic energetic cycle enabled by the unique molecular machinery of electron transport chains in photosystems and respiratory chains facilitated the striking success of life on Earth. Biomolecules 2019, 9, 266 once in evolutionary history and have been transferred to various eukaryotic life forms only through plastid and mitochondrial endosymbioses
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
