Functional Analysis of Tocopherols in Plants and their Integration within the Plastid Antioxidant Network

在植物的整个生命周期中，植物暴露于广泛的非生物和生物胁迫中，这些胁迫会导致活性氧物种(ROS)的产生超过正常代谢产生的ROS，并在没有胁迫的情况下作为信号传递。虽然所有的亚细胞室都会产生ROS，但叶绿体是光合作用组织中ROS的主要来源。为了避免氧化损伤和死亡，植物进化出了一个相互关联的互补网络，包括化合物(如抗坏血酸、生育酚、类胡萝卜素、谷胱甘肽)、酶(如超氧化物歧化酶、过氧化氢酶、过氧化氢酶)和生化反应(如非光化学猝灭)，这些化合物在胁迫条件下可最大限度地减少叶绿体ROS的产生，或快速解毒过量的ROS物种或产生的副产物。生育酚，通常被称为维生素E，是叶绿体中主要的脂溶抗氧化剂，被认为是叶绿体抗氧化网络的重要组成部分。在哺乳动物和人造膜上的研究表明，生育酚对膜结构、单线态氧和其他ROS的猝灭、清除链传播的脂质过氧化自由基以及其他与信号和转录调节相关的非抗氧化功能具有重要作用。在植物中，生育酚的作用被认为是相似的，尽管缺乏实验证据。在过去的五年中，Dellapenna实验室克隆了拟南芥生育酚生物合成途径的所有酶，并培育出叶片中生育酚完全缺乏或累积水平是野生型水平4-5倍的突变/转基因品系。这些生育酚修饰品系将被用于：1.确定生育酚在清除特定ROS物种和控制脂质过氧化中的作用(S)。2.在与影响抗氧化网络其他成分的突变的遗传组合中，评估抗氧化网络成分的功能补偿和冗余性。研究生育酚缺失品系的一种新的萌发表型。在全基因组表达分析中，评估单个抗氧化网络基因和其他细胞成分对生育酚修饰的反应。生育酚，通常被称为维生素E，是所有植物叶绿体中主要的脂溶抗氧化剂，被认为是叶绿体抗氧化网络的重要组成部分。正在进行的研究将提供一个全面的了解生育酚在拟南芥的光合作用组织中的功能(S)。这项工作还将定义和表征生育酚与叶绿体抗氧化剂网络的其他组成部分(维生素C、类胡萝卜素和清除活性氧的酶)的整合和互补。由于叶绿体中抗氧化剂网络的进化保守，所获得的数据将与广泛的植物物种和作物直接相关。

During its lifecycle, a plant is exposed to a wide range of abiotic and biotic stresses that can cause production of reactive oxygen species (ROS) in excess of that normally generated by metabolism and for signaling in the absence of stress. Although all subcellular compartments produce ROS, chloroplasts are the major ROS source in photosynthetic tissues. In order to avoid oxidative damage and death, plants have evolved an interconnected, complementary network of compounds (e.g., ascorbate, tocopherols, carotenoids, glutathione), enzymes (e.g., superoxide dismutases, peroxidases, catalases) and biochemical responses (e.g., non-photochemical quenching) that serve to minimize plastid ROS production under stressful conditions or rapidly detoxify excess ROS species or byproducts that are produced. Tocopherols, more commonly known as Vitamin E, are the major lipid soluble antioxidant in plastids and are proposed to be an essential component of the plastid antioxidant network. Studies in mammals and artificial membranes indicate tocopherols are important for membrane structure, quenching of singlet oxygen and other ROS, scavenging of chain-propagating lipid peroxy radicals and other "non-antioxidant" functions related to signaling and transcriptional regulation. In plants, tocopherols are assumed to function similarly though experimental evidence for this is lacking. During the past five years, the DellaPenna laboratory has cloned all enzymes of the tocopherol biosynthetic pathway in Arabidopsis and developed mutant/transgenic lines whose leaves are completely deficient in tocopherols or accumulate tocopherols at 4-5 times wild type levels. These tocopherol-modified lines will be used:1. To define the role(s) of tocopherols in scavenging specific ROS species and control of lipid peroxidation. 2. In genetic combinations with mutations that affect other components of the antioxidant network to assess functional compensation and redundancy of antioxidant network components.3. To study a novel germination phenotype in tocopherol deficient lines.4. In whole genome expression analysis to assess the response of individual antioxidant network genes and other cellular components to tocopherol modifications. Tocopherols, more commonly known as Vitamin E, are the major lipid soluble antioxidant in chloroplasts of all plants and are proposed to be an essential component of the plastid antioxidant network. The research being undertaken will provide a comprehensive understanding of tocopherol function(s) in photosynthetic tissues of Arabidopsis. This work will also define and characterize the integration and complementation of tocopherols with and by other components of the plastid antioxidant network (Vitamim C, carotenoids and enzymes that scavenge reactive oxygen). Because of the evolutionary conservation of the antioxidant network in chloroplasts, the data obtained will be of direct relevance to a wide range of plant species and crops.