Finessing, Extending and Developing an Overview of the Regulation of Ascorbate in plants (FEDORA)

从真核藻类到被子植物，抗坏血酸是所有植物的关键代谢物。它是最丰富的水溶性抗氧化剂，在光合作用、跨膜电子传递、细胞分裂、生长以及对生物和非生物胁迫的耐受等方面发挥着重要作用。它发挥着不同的作用，主要是作为光合作用的副产品产生的活性氧的清除剂，在水-水循环中耗散多余的光子能量，以及作为叶黄素循环中的辅助因子。它是双加氧酶的辅因子，在植物激素、乙烯、脱落酸和赤霉素的合成以及羟脯氨酸的合成中发挥作用，对修饰CLAVATA3和阿拉伯半乳糖蛋白(AGPs)等小信号肽很重要，这些蛋白多糖是普遍存在的细胞表面蛋白多糖，在植物的生长和发育中发挥重要作用，包括细胞扩张、细胞分裂、生殖发育和体细胞胚胎发生。因此，抗坏血酸水平的调节是所有植物生长发育中大量生理过程的关键。有大量的文献描述了影响抗坏血酸水平的过程，但描述调节机制的文献非常少，特别是在分子水平上。不用说，这种对机理的缺乏限制了我们通过生物技术或植物育种来设计依赖于抗坏血酸的过程以进行作物改良的能力。这一限制甚至延伸到提高新鲜水果和蔬菜中抗坏血酸水平的努力，尽管最近有令人震惊的报告称，由于抗坏血酸/维生素C缺乏而导致坏血病的发病率增加。例如，在英国，2009至2014年间，由于营养不良和过度食用垃圾食品导致的肥胖，与坏血病相关的住院人数上升了27%。这一切都被Laing等人于2015年发表在《植物细胞》上的两篇里程碑式的论文所改变，一篇是由Laing等人于2015年在《植物细胞》上发表的，展示了一种独特的负反馈调节机制控制Gdp-L-半乳糖磷酸化酶(GGP)的翻译，GGP是一种活跃在Smirnoff-Wheeler抗坏血酸合成途径中的酶，另一篇由Fenech等人在《植物生理学》(2021年)上发表，表明GGP活性是决定植物组织中抗坏血酸水平的唯一重要控制步骤，并表明GGP活性几乎是通过Smirnoff-Wheeler途径对通量的线性控制。这一应用的目的是整合我们对植物细胞中抗坏血酸调节的理解。我们的目标是确定GGP翻译负反馈调控的分子机制，并了解GGP的翻译控制是如何设置在转录控制所定义的边界内的。我们建议理解GGP活性的控制如何影响抗坏血酸的流量。我们建议通过主要研究拟南芥和番茄这两个植物物种来整合我们对调控机制的研究，以发展对植物调控机制的普遍理解，使其具有广泛的适用性。我们建议通过合作扩大我们对GGP对绿藻负反馈调控机制的理解。为了了解抗坏血酸在不同植物中的生理作用，我们将研究一系列错误调节抗坏血酸水平的GGP突变体的表型后果，并确定在拟南芥中观察到的表型效应是相似的还是不同的。

Ascorbate is a key metabolite for all plants, from eukaryotic algae to angiosperms. It is the most abundant water-soluble antioxidant with major roles in photosynthesis, transmembrane electron transport, cell division, growth and tolerance of biotic and abiotic stress. It performs these diverse roles by serving as a major scavenger of active oxygen species generated as by-products of photosynthesis, in the dissipation of excess photonic energy through the water-water cycle and as a co-factor in the xanthophyll cycle. It serves as a cofactor for dioxygenases, which are active in the synthesis of the phytohormones, ethylene, abscisic acid and gibberellins and in the generation of hydroxyproline, important for decorating small signalling peptides like CLAVATA3 and arabinogalactan-proteins (AGPs), which are ubiquitous cell surface proteoglycans proposed to play essential roles in plant growth and development, including cell expansion, cell division, reproductive development and somatic embryogenesis. Consequently the regulation of ascorbate levels is key to a large number of physiological processes in the growth and development of all plants.There is a vast body of literature describing the processes that influence ascorbate levels, but remarkably few papers describe the mechanisms of regulation, particularly at the molecular level. Needless to say, this lack of understanding of mechanism has limited our ability to engineer processes dependent on ascorbate through biotechnology or plant breeding for crop improvement. This limitation extends even to efforts to enhance ascorbate levels in fresh fruit and vegetables, despite the alarming reports of recent increases in the incidence of scurvy resulting from ascorbate/vitamin C deficiency. For example, in the UK between 2009 and 2014, hospital admissions related to scurvy went up by 27% due to malnutrition and obesity related to over-consumption of junk food diets. All that was changed by the publication of two landmark papers, one by Laing et al., in The Plant Cell in 2015 demonstrating a unique negative feedback regulatory mechanism controlling the translation of GDP-L-galactose phosphorylase (GGP) an enzyme active in the Smirnoff-Wheeler pathway for ascorbate synthesis, and the other by Fenech et al., in Plant Physiology (2021) showing that GGP activity is the only significant controlling step determining ascorbate levels in plant tissues and shows almost linear control of flux through the Smirnoff-Wheeler pathway.The aim of this application is to integrate our understanding of the regulation of ascorbate in plant cells. We aim to define the molecular mechanism for the negative feedback regulation of GGP translation and to understand how translational control of GGP is set within the boundaries defined by transcriptional control. We propose to understand how the control of GGP activity impacts flux to ascorbate. We propose to integrate our investigations of the mechanisms of regulation by studying primarily two plant species, Arabidopsis and tomato, to develop generic understanding of mechanisms for plants that could be broadly applicable. We propose to extend our understanding of the mechanism of negative feedback regulation of GGP to green algae through collaboration. To understand the physiological roles of ascorbate in different plant species we will investigate the phenotypic consequences of a series of GGP mutants with mis-regulated ascorbate levels, and determine whether similar or different phenotypic effects are observed in Arabidopsis.