Evolution of Photosynthesis

Abstract Photosynthesis originated once during the early Archaean due to the emergence of photochemical reaction centres, the biological nanomachines that convert the energy of light into chemical energy. The evolution of the photosynthetic machinery is consistent with a single origin of photosynthesis followed by an early diversification event that resulted in the rapid evolution of distinct reaction centre types and pigment forms. One of these reaction centres specialised in highly oxidising photochemistry, which facilitated the oxidation of Mn and the evolution of the water‐oxidising cluster of Photosystem II . In addition, the last common ancestor of all photosynthetic organisms can be traced back to a period of time near the root or at the root of the tree of life of bacteria, with the current distribution of photosynthesis being the result of widespread loss of photosynthetic capacity and horizontal gene transfer. Key Concepts Photosynthesis originated at least 3.5 billion years ago, but it could be much older. Photosynthesis evolved only once in ancestral forms of bacteria. Type I and Type II reaction centres originated from an ancestral gene duplication event. The last common ancestor of photosynthetic bacteria had type I and type II reaction centres. Photosystem II originated from the close interaction of a Type I and Type II reaction centre. The ancestral homodimeric Photosystem II was able to catalyse the oxidation of water. The last common ancestor of photosynthetic bacteria had protochlorophyllide and chlorophyllide reductase and could make pigments similar to chlorophyll a and bacteriochlorophyll g . Nitrogenase and the chlorophyll synthesis enzymes originated from an ancient gene duplication event predating the diversification of bacteria. The current distribution of photosynthesis in bacteria is explained by widespread loss of photosynthesis and horizontal gene transfer.