Chemifortification of leaves through enhanced metabolic flux to tocopherol biosynthesis and plastoglobule proliferation.

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 chemifortification approach independent of genetic manipulation. A chemical screening identified X57, a synthetic compound that simultaneously activates all three mechanisms to enhance leaf tocopherol content. Besides their dietary value as vitamin E, tocopherols protect plants against oxidative stress and they are highly appreciated antioxidants in food and cosmetic formulations. X57 exerts a primary “push” effect by inducing tocopherol biosynthesis, in part by reactivating a direct pathway that reduces geranylgeranyl diphosphate (GGPP) to phytyl diphosphate, 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 (PG), plastidial lipoprotein bodies that synthesize and store tocopherols. X57-induced PG proliferation is driven by increased tocopherol levels and upregulation of genes for PG structural proteins such as fibrillins. X57 thus provides a powerful chemical tool for non-genetic vitamin E biofortification but also to better understand the coordination of plastidial isoprenoid metabolism and plastid differentiation. Overall design: RNA-seq profiling of 5-day-old Arabidopsis thaliana seedlings treated with the chemical compound X57 or with mock conditions (0.05% DMSO) for 5 hours.

利用植物营养素开展植物生物强化，通常依赖于被称为“push”（增强生物合成通量）、“block”（抑制竞争代谢通路）以及“pull”（促进代谢物储存）的代谢工程策略。本研究报道一种无需基因操作的新型化学生物强化方法。通过化学筛选获得合成化合物X57，其可同时激活上述三种机制，以提升叶片生育酚（tocopherol）含量。生育酚除作为维生素E的膳食来源外，还可帮助植物抵御氧化应激，同时也是食品与化妆品配方中广受青睐的抗氧化剂。X57主要通过“push”效应发挥作用：它可诱导生育酚的生物合成，部分机制是重新激活一条将牻牛儿基牻牛儿基二磷酸（GGPP）还原为植基二磷酸的直接通路，从而无需依赖叶绿素衍生的植醇。据此，X57可在黄化幼苗中促进生育酚积累，并在植醇磷酸化缺陷的突变体中恢复生育酚合成。其“block”效应通过下调用于类胡萝卜素合成的GGPP消耗来介导。X57还可通过质体小球（plastoglobules, PG）的增殖发挥“pull”效应——质体小球是合成并储存生育酚的质体脂蛋白颗粒。X57诱导的质体小球增殖由生育酚水平升高以及质体小球结构蛋白（如原纤维蛋白）的基因上调所驱动。因此，X57不仅是一款强大的非遗传维生素E生物强化化学工具，还可用于深入解析质体类异戊二烯代谢与质体分化的协同调控机制。整体实验设计：对经化合物X57或0.05%二甲基亚砜（DMSO）模拟处理5小时的5日龄拟南芥（Arabidopsis thaliana）幼苗开展RNA测序（RNA-seq）转录组分析。