Regulation of Tocopherol (Vitamin E) biosynthesis in <i>Arabidopsis</i>

Tocochromanols, including tocopherols and tocotrienols, encompass a group of lipid antioxidants that are synthesized in chloroplasts of photosynthetic organisms. Tocochromanols are essential for mammals, because they provide vitamin E activity. In plants, tocochromanols can scavenge reactive oxygen species derived from photosynthesis. While most dicot plants including Arabidopsis thaliana produce tocopherols with a saturated side chain, tocotrienols carrying an unsaturated side chain are found in many monocot plants. Here, we present an overview on the current knowledge about the biosynthesis of tocopherols, with a focus on the origin of the head group and side chain precursors, and the regulation of tocopherol synthesis by abiotic stress and phytohormones. The chromanol headgroup is derived from tyrosine which is synthesized via the shikimate pathway, while the phytyl side chain originates from chlorophyll turnover. Tocopherol synthesis is regulated during different abiotic stress conditions, including high light, drought, heat, cold and salt stress. Furthermore, different phytohormones like jasmonate, abscisic acid, gibberellins, brassinosteroids and salicylate are involved in the regulation of tocopherol synthesis. The control of stress- and phytohormone-dependent tocopherol synthesis is mostly based on the regulation on the transcriptional level of key genes of tocopherol synthesis.