Photorespiration: players, partners and origin.

Photorespiratory metabolism allows plants to thrive in a high-oxygen containing environment. This metabolic pathway recycles phosphoglycolate, a toxic compound, back to phosphoglycerate, when oxygen substitutes for carbon dioxide in the first reaction of photosynthetic carbon fixation. The recovery of phosphoglycerate is accompanied by considerable carbon and energy losses, making photorespiration a prime target for crop improvement. The genomics era has allowed the precise functional analysis of individual reaction steps of the photorespiratory cycle, and more links integrating photorespiration with cellular metabolism as a whole are becoming apparent. Here we review the evolutionary origins of photorespiration as well as new insights into the interaction with other metabolic processes such as nitrogen assimilation and mitochondrial respiration.