Evolutionary insights into strategy shifts for the safe and effective accumulation of ascorbate in plants.

This article focuses on the evolutionary transitions in plant ascorbate (vitamin C) metabolism, particularly the regulatory mechanisms of ascorbate biosynthesis and the management of its oxidized form, dehydroascorbate (DHA). It highlights two main shifts: first, the trigger for transcriptional induction of VTC2, encoding the rate-limiting enzyme GDP-l-galactose phosphorylase (GGP) in the d-mannose/l-galactose pathway, changed from oxidative stress in green algae to light/photosynthesis in land plants, enabling continuous ascorbate accumulation under illumination. Second, while green algae and mosses possess DHA-degrading enzymes (DHA lactonases) to mitigate DHA toxicity, these enzymes were lost in ferns and flowering plants, which instead increased glutathione concentrations to enhance DHA reduction capacity and safely accumulate higher ascorbate levels. The article also discusses the co-evolution of ascorbate recycling enzymes—dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDAR)—with ascorbate peroxidases (APX) across subcellular compartments, emphasizing the complementary roles of enzymatic and glutathione-dependent non-enzymatic DHA reduction in maintaining ascorbate redox balance. These evolutionary adaptations likely facilitated plants’ enhanced antioxidant capacity and environmental stress tolerance during terrestrialization.