Photorespiratory Metabolism: Genes, Mutants, Energetics, and Redox Signaling

Photorespiration is a high-flux pathway that operates alongside carbon assimilation in C3 plants. Because most higher plant species photosynthesize using only the C3 pathway, photorespiration has a major impact on cellular metabolism, particularly under high light, high temperatures, and CO2 or water deficits. Although the functions of photorespiration remain controversial, it is widely accepted that this pathway influences a wide range of processes from bioenergetics, photosystem II function, and carbon metabolism to nitrogen assimilation and respiration. Crucially, the photorespiratory pathway is a major source of H2O2 in photosynthetic cells. Through H2O2 production and pyridine nucleotide interactions, photorespiration makes a key contribution to cellular redox homeostasis. In so doing, it influences multiple signaling pathways, particularly those that govern plant hormonal responses controlling growth, environmental and defense responses, and programmed cell death. The potential influence of photorespiration on cell physiology and fate is thus complex and wide ranging. The genes, pathways, and signaling functions of photorespiration are considered here in the context of whole plant biology, with reference to future challenges and human interventions to diminish photorespiratory flux.