A Chemical Probe for Increasing Leaf Tocopherol Levels by Coordinated Modulation of Biosynthesis, Competition and Storage

[EN] Plant biofortification with phytonutrients typically relies on metabolic engineering strategies known as “push” (enhancing biosynthetic flux), “block” (inhibiting competing pathways), and “pull” (promoting metabolite storage). Here, we describe a novel synthetic compound, X57, that simultaneously targets biosynthesis, competition, and storage to enhance leaf tocopherol content. Tocopherols protect plants against oxidative stress, have dietary value as vitamin E, and are widely used as antioxidants in food and cosmetic formulations. X57 exerts a primary “push” effect by inducing tocopherol biosynthesis, partly through reactivating a direct pathway that reduces geranylgeranyl diphosphate (GGPP) to phytyl diphosphate, thereby bypassing the need for chlorophyll-derived phytol. Accordingly, X57 promotes tocopherol accumulation in etiolated seedlings and restores tocopherol synthesis in mutants deficient in phytol phosphorylation. The “block” effect is mediated by downregulation of GGPP consumption for carotenoid synthesis. X57 also induces a “pull” effect via proliferation of plastoglobules (PGs), plastidial lipoprotein bodies that synthesize and store tocopherols. X57-induced PG proliferation is driven by increased tocopherol levels and upregulation of genes encoding PG structural proteins such as fibrillins. The genetic networks coordinating plastidial isoprenoid metabolism and plastid differentiation may be specific to higher plants, as X57 does not promote—and instead reduces—tocopherol accumulation in Marchantia polymorpha.