Photorespiration and the Evolution of C4Photosynthesis

C 4 photosynthesis is one of the most convergent evolutionary phenomena in the biological world, with at least 66 independent origins. Evidence from these lineages consistently indicates that the C 4 pathway is the end result of a series of evolutionary modifications to recover photorespired CO 2 in environments where RuBisCO oxygenation is high. Phylogenetically informed research indicates that the repositioning of mitochondria in the bundle sheath is one of the earliest steps in C 4 evolution, as it may establish a single-celled mechanism to scavenge photorespired CO 2 produced in the bundle sheath cells. Elaboration of this mechanism leads to the two-celled photorespiratory concentration mechanism known as C 2 photosynthesis (commonly observed in C 3 –C 4 intermediate species) and then to C 4 photosynthesis following the upregulation of a C 4 metabolic cycle.