Regulatory Crosstalk Between Tocopherol Biosynthesis and Chlorophyll Metabolism in Plants: Current Insights.

Plants produce a wide array of bioactive compounds that are essential for both plants and humans. Among those compounds, tocopherols (vitamin E) are lipid-soluble antioxidants that play key roles in plant protection and human health. Precursors of tocopherols are homogentisic acid (HGA) and phytyl diphosphate (PDP). It has long been established that PDP is primarily synthesized de novo via the plastidial 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. However, studies in Arabidopsis thaliana, maize, and tomato showed that phytol, a byproduct of chlorophyll degradation, can be synthesized into PDP and utilized for tocopherol production. The studies have demonstrated metabolic and genetic links between chlorophyll metabolism and tocopherol synthesis through phytol recycling, as evidenced by transgenic lines, genome-wide association studies, and light-intensity treatments. While previous reviews have focused mainly on the core tocopherol biosynthesis pathway and its regulation, this integration of chlorophyll degradation-derived phytol recycling with genetic and environmental regulation is rarely discussed. Therefore, the recent information prompted us to conduct a comprehensive literature review that integrates metabolic, genetic, and environmental factors underlying the relationship between chlorophyll metabolism and tocopherol synthesis in plants. This review aims to gather current knowledge on this relationship, highlight its biological and environmental significance, and discuss potential applications for biofortification.