Plant oxalate oxidases: key enzymes in redox and stress regulation

Oxalate oxidases (OXOs) are integral to plant physiology, facilitating the degradation of oxalate (oxalic acid) into hydrogen peroxide (H₂O₂) and carbon dioxide. OXOs are considered a key source of H₂O₂ in plant cells, especially under oxidative stress, which activates diverse physiological roles, including cell wall fortification, redox signaling, and modulation of ion homeostasis. As a result, OXOs significantly influence embryo viability, cell wall stiffening, apoplastic redox activity, and defense, especially under abiotic stresses such as drought, salinity, and temperature. Additionally, OXO-generated H₂O₂ can reinforce innate immunity against fungal and bacterial pathogens, highlighting its role in both abiotic and biotic stress tolerance. Recent research suggests that OXO-mediated reactive oxygen species bursts modulate cell division processes, metabolic pathways, and potentially photosynthesis, although many mechanistic details remain to be elucidated. Beyond plant physiology, OXOs hold industrial and medical interest. Degrading oxalate helps in preventing pulp and paper processing scaling, reduces oxalate in certain foods, and may support therapeutic interventions for oxalate-related diseases. Ongoing efforts to improve heterologous expression and enzyme engineering aim to enhance production efficiency, stability, and specificity. This review synthesizes current knowledge on OXO structure–function relationships, their physiological importance across multiple plant species, and the emerging avenues for biotechnological exploitation. While commercial applications show promise, deeper insight into the mechanics of OXOs is needed to harness their capabilities fully.