The recurrent assembly of C4 photosynthesis, an evolutionary tale

Today, plants using C-4 photosynthesis are widespread and important components of major tropical and subtropical biomes, but the events that led to their evolution and success started billions of years ago (bya). A CO2-fixing enzyme evolved in the early Earth atmosphere with a tendency to confuse CO2 and O-2 molecules. The descendants of early photosynthetic organisms coped with this property in the geological eras that followed through successive fixes, the latest of which is the addition of complex CO2-concentrating mechanisms such as C-4 photosynthesis. This trait was assembled from bricks available in C-3 ancestors, which were altered to fulfill their new role in C-4 photosynthesis. The existence of C-4-suitable bricks probably determined the lineages of plants that could make the transition to C-4 photosynthesis, highlighting the power of contingency in evolution. Based on the latest findings in C-4 research, we present the evolutionary tale of C-4 photosynthesis, with a focus on the general evolutionary phenomena that it so wonderfully exemplifies.