Alternative Oxidase of Plant Mitochondria

植物线粒体的替代氧化酶

• 批准号: RGPIN-2014-06553
• 负责人: Vanlerberghe, Greg
• 金额: $ 2.91万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=567885
• 关键词: Alternative; Oxidase; Plant; Mitochondria

Alternative oxidase (AOX) is a non-energy conserving terminal oxidase in the plant mitochondrial electron transport chain that relaxes the coupling between respiratory carbon oxidation, electron transport, and ATP turnover. Despite key advances in our understanding of the genetic and biochemical control of AOX, the role of this auxiliary respiratory pathway in plant metabolism and mitochondrial physiology, as well as its overall impact on plant growth and performance remains poorly understood. As often highlighted in influential reviews, this represents a major gap in our understanding of plant primary metabolism. AOX gene expression is highly responsive to environmental cues and some evidence indicates that the pathway may be of particular importance under variable and stress conditions. Theoretically, AOX should negatively impact growth since it reduces ATP yield. However, it may have key roles in metabolism and mitochondrial physiology that outweigh this energy cost. My research proposal has two broad scientific goals. The first is to establish the role of AOX in supporting leaf metabolism. An emphasis will be to elucidate the mechanisms by which AOX supports photosynthesis. Our preliminary work shows that during drought stress, photosynthesis is strongly compromised in transgenic plants lacking AOX. Gas exchange and chlorophyll fluorescence analyses indicate that this is the result of a severe biochemical (rather than stomatal) limitation in plants lacking AOX. Detailed physiological and biochemical analyses will elucidate the nature of this limitation. We will also investigate the interaction of AOX and photosynthesis in plants grown at ambient versus high CO2. High CO2 has the potential to increase photosynthetic rate but can result instead in a down-regulation of photosynthetic capacity, such that the potential for higher source activity is not met. The propensity for such down-regulation depends strongly upon the response of sinks to high CO2. While respiration is a critical sink activity, little is known regarding specifically AOX at high CO2. This is a major gap in our understanding of how photosynthesis and growth will be impacted by future high CO2 conditions. A second broad scientific goal of the research proposal is to establish the role of AOX in supporting mitochondrial physiology. An emphasis will be elucidating the role of AOX in supporting the signaling function of mitochondria. Mitochondria act as signaling organelles involved in stress acclimation, but the primary “signals” from mitochondria that are involved in such responses are unknown. Our proposal builds upon a major finding from our previous work, where biochemical and confocal imaging analyses established that AOX controls the ETC generation of superoxide and nitric oxide, reactive species that can act as damaging molecules or signaling molecules within the cell. These reactive species, along with downstream products (hydrogen peroxide, peroxynitrite) are lead candidates as signal molecules for stress acclimation. Our ability to manipulate the level of these molecules using plants with altered AOX amount provides a powerful strategy to test hypotheses regarding the signaling capability of specific reactive oxygen and nitrogen species emanating from a specific cell compartment, the mitochondrion. We will investigate this signaling capability in support of stress acclimation responses at both the molecular level (ie. changes in nuclear gene expression) and cell level (ie. guard cell movements). Another important overall goal of the research proposal is the mentorship and training of three postdoctoral fellows, eight graduate students and numerous undergraduates. This will include a fostering of independence and multidisciplinary work.

尽管我们对 AOX 的遗传和生化控制的理解取得了重大进展，但替代氧化酶 (AOX) 是植物线粒体电子传递链中的一种非能量守恒末端氧化酶，可放松呼吸碳氧化、电子传递和 ATP 周转之间的耦合。 ，这种辅助呼吸途径在植物代谢和线粒体生理学中的作用，以及它对植物生长和性能的总体影响仍然知之甚少，正如有影响力的评论中经常强调的那样，这代表了我们的主要差距。 AOX 基因表达对环境因素高度敏感，并且一些证据表明该途径在变化和胁迫条件下可能特别重要。理论上，AOX 应该对生长产生负面影响，因为它会降低 ATP 产量。我的研究计划有两个广泛的科学目标，第一个是确定 AOX 在支持叶子代谢中的作用，重点是阐明 AOX 支持的机制。我们的初步工作表明，在干旱胁迫下，缺乏 AOX 的转基因植物的光合作用受到严重损害。 气体交换和叶绿素荧光分析表明，这是缺乏 AOX 的植物中严重的生化（而不是气孔）限制的结果。生化分析将阐明这种限制的本质，我们还将研究在环境条件下生长的植物与高二氧化碳条件下生长的植物的光合作用之间的相互作用。光合速率，但可能导致光合能力下调，从而无法满足更高源活动的潜力。这种下调的倾向很大程度上取决于汇对高二氧化碳的反应。我们对高二氧化碳条件下的 AOX 的具体情况知之甚少，这是我们对未来高二氧化碳条件如何影响光合作用和生长的理解的一个主要差距。 AOX 支持线粒体生理学。重点是阐明 AOX 在支持线粒体信号传导功能中的作用，线粒体作为参与应激适应的信号细胞器，但参与此类反应的线粒体的主要“信号”尚不清楚。我们的建议建立在我们之前工作的一项重大发现的基础上，其中生化和共聚焦成像分析证实，AOX 控制 ETC 超氧化物和一氧化氮的生成，这些活性物质可以充当破坏性分子或信号分子这些活性物质以及下游产物（过氧化氢、过氧亚硝酸盐）是作为应激适应信号分子的主要候选者，我们利用改变 AOX 含量的植物来操纵这些分子的水平，为检验假设提供了强大的策略。关于从特定细胞室（线粒体）发出的特定活性氧和氮的信号传导能力，我们将研究这种信号传导能力，以支持分子水平（即核基因表达的变化）和细胞水平的应激适应反应。 （即保卫细胞运动）。该研究计划的另一个重要总体目标是指导和培训三名博士后研究员、八名研究生和众多本科生，这将包括培养独立性和多学科工作。