Evolution of the biochemistry of the photorespiratory C 2 cycle

Oxygenic photosynthesis would not be possible without photorespiration in the present day O 2 ‐rich atmosphere. It is now generally accepted that cyanobacteria‐like prokaryotes first evolved oxygenic photosynthesis, which was later conveyed via endosymbiosis into a eukaryotic host, which then gave rise to the different groups of algae and streptophytes. For photosynthetic CO 2 fixation, all these organisms use Rubis CO , which catalyses both the carboxylation and the oxygenation of ribulose 1,5‐bisphosphate. One of the reaction products of the oxygenase reaction, 2‐phosphoglycolate (2 PG ), represents the starting point of the photorespiratory C 2 cycle, which is considered largely responsible for recapturing organic carbon via conversion to the Calvin–Benson cycle ( CBC ) intermediate 3‐phosphoglycerate, thereby detoxifying critical intermediates. Here we discuss possible scenarios for the evolution of this process toward the well‐defined 2 PG metabolism in extant plants. While the origin of the C 2 cycle core enzymes can be clearly dated back towards the different endosymbiotic events, the evolutionary scenario that allowed the compartmentalised high flux photorespiratory cycle is uncertain, but probably occurred early during the algal radiation. The change in atmospheric CO 2 / O 2 ratios promoting the acquisition of different modes for inorganic carbon concentration mechanisms, as well as the evolutionary specialisation of peroxisomes, clearly had a dramatic impact on further aspects of land plant photorespiration.