Photorespiration: current status and approaches for metabolic engineering

Photorespiration results from the oxygenase reaction catalysed by ribulose-1,5-bisphosphate carboxylase/oxygenase and serves as a carbon recovery system. It comprises enzymatic reactions distributed in chloroplasts, peroxisomes and mitochondria. The recent discovery of a cytosolic bypass and the requirement of complex formation between some photorespiratory proteins added additional levels of complexity to the known pathway. Photorespiration may have evolved in both, C3 and C4 plants, to prevent an accumulation of toxic levels of glycolate. Moreover, it is suggested that photorespiration evolved in cyanobacteria before the origin of chloroplasts. Synthetic detours, reminiscent of secondary photorespiratory pathways naturally occurring in cyanobacteria, were installed in Arabidopsis thaliana to bypass photorespiration. An enrichment of CO2 in the chloroplast and positive effects on plant growth raised the question why these pathways have been lost from higher plants.