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: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=630298
• 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.

交替氧化酶（AOX）是植物线粒体电子传递链上的一种非能量守恒的末端氧化酶，其作用是放松呼吸碳氧化、电子传递和ATP周转之间的耦合。尽管我们对AOX的遗传和生化控制的理解取得了关键进展，但这种辅助呼吸途径在植物代谢和线粒体生理学中的作用，以及其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，这代表了我们对植物初级代谢理解的一个主要差距。AOX基因的表达对环境信号高度敏感，一些证据表明，该途径在可变和胁迫条件下可能特别重要。从理论上讲，AOX应该会对生长产生负面影响，因为它会降低ATP产量。然而，它可能在代谢和线粒体生理学中发挥关键作用，超过这种能量消耗。我的研究计划有两个广泛的科学目标。首先是确定AOX在支持叶片代谢中的作用。重点将是阐明AOX支持光合作用的机制。我们的初步工作表明，在干旱胁迫下，光合作用强烈受损的转基因植物缺乏AOX。气体交换和叶绿素荧光分析表明，这是一个严重的生物化学（而不是气孔）的限制，在植物缺乏AOX的结果。详细的生理和生化分析将阐明这种限制的性质。我们还将研究AOX和光合作用在植物生长在环境与高CO2的相互作用。高CO2具有增加光合速率的潜力，但可能反而导致光合能力的下调，使得更高的源活性的潜力得不到满足。这种下调的倾向强烈地依赖于汇对高CO2的反应。虽然呼吸作用是一个关键的汇活动，很少有人知道具体AOX在高CO2。这是我们理解光合作用和生长将如何受到未来高CO2条件影响的主要差距。该研究提案的第二个广泛的科学目标是确定AOX在支持线粒体生理学中的作用。重点将是阐明AOX在支持线粒体信号功能中的作用。线粒体作为参与应激适应的信号细胞器，但参与这种反应的线粒体的主要“信号”是未知的。我们的建议建立在我们以前工作的一个主要发现的基础上，其中生化和共聚焦成像分析确定AOX控制超氧化物和一氧化氮的ETC生成，这些活性物质可以作为细胞内的破坏分子或信号分子。这些活性物质，沿着下游产物（过氧化氢，过氧亚硝酸盐）是应激适应信号分子的主要候选者。我们的能力，操纵这些分子的水平，使用改变AOX量的植物提供了一个强大的策略，以测试有关特定的活性氧和氮物种从一个特定的细胞隔室发出的信号能力的假设，的细胞色素。我们将研究这种信号传导能力，以支持在分子水平上的应激适应反应（即。核基因表达的变化）和细胞水平（即，保卫细胞运动）。研究提案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。这将包括促进独立性和多学科工作。