Global significance of light-driven proton pumps in eukaryotic marine phytoplankton

光驱动质子泵在真核海洋浮游植物中的全球意义

• 批准号: NE/K013734/1
• 负责人: Thomas Mock
• 金额: $ 38.33万
• 依托单位: University of East Anglia
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FK013734%2F1
• 关键词: Global; significance; light; driven; proton

Sunlight is the ultimate source of energy on our planet and the efficient capture and use of light is an exquisitely evolved process across all kingdoms of life, ranging from unicellular microbes to multicellular organisms. In addition to use of light as an energy source for growth, it is also an important source of environmental information. Microbes have evolved particularly diverse systems to use light to generate energy, avoid hostile environments and identify suitable environments for nutrition and growth. The metabolic mode in which organisms convert light energy into chemical energy for growth is called phototrophy (from Greek [photo-], "light" and [trophe], "nourishment"). The most important biological process on earth to power phototrophy is oxygenic photosynthesis, which employs multisubunit protein complexes containing chlorophyll pigments known as photosystems and produces the oxygen we breathe. These photosystems are highly-efficient in capturing and using light, but heavily-depend on iron to function.Additionally, a second mechanistically distinct process, which is independent from photosystems, can also power phototrophy and employs membrane-embedded photoreceptors called rhodopsins. Rhodopsins are molecules composed of opsin membrane proteins, which bind the pigment retinal but unlike photosystems do not need iron to function. Their operating principle is based on their unitary simple nature. Instead of employing complex photosystems, which are encoded by multiple genes, rhodopsins combine the tasks of light absorption and energy-conservation into a single protein encoded by a single gene. Upon absorption of light, the chemical structure of retinal pigment changes and triggers a cascade of structural changes within the molecule. Rhodopsin photoreceptors were first discovered in ancient prokaryotic (cells lacking a nucleus and membrane-bound organelles) archaebacteria, but later also in very distantly related bacteria. The high abundance of bacterial rhodopsins in marine environments has shown that rhodopsin-based phototrophy is a globally significant microbial process in the ocean. Surprisingly, rhodopsins have recently also been identified in unicellular eukaryotes (organisms with nucleus and nuclear envelope enclosing the genetic material) including photosynthetic marine phytoplankton. However, the function of eukaryotic rhodopsins in the presence of more energy-efficient photosystems remains puzzling. In a preliminary study, we provided first experimental evidence, that genes encoding for rhodopsins are highly up-regulated in iron-limited phytoplankton. They were also more abundant in iron-limited oceans, which cover about one third of the global ocean surface. These findings provide first direct evidence for our research hypothesis that rhodopsins in marine phytoplankton provide a previously unknown backup mechanism for iron-dependent chlorophyll-based photosynthesis, to enhance production of chemical energy and growth when iron is lacking for iron-dependent photosystems. This new mechanism is of particular interest, because recent research has shown that ocean acidification due to increased dissolution of anthropogenic carbon dioxide can decrease the iron availability to phytoplankton, which probably will alter phytoplankton diversity in the oceans and favor species that have a competitive advantage (e.g. by rhodopsin-based phototrophy) under reduced iron concentrations. In our research project we will use new molecular genetic methods to test our research hypothesis and further explore the cellular role and environmental significance of rhodopsins in globally important marine phytoplankton. Our results will provide fundamental new insights into how marine phytoplankton use rhodopsins. It will be of great interest to the scientific community, because phytoplankton are subject to many different disciplines, from marine and climate science to material science and renewable energy.

阳光是我们星球上能量的最终来源，从单细胞微生物到多细胞生物，所有生命王国都在巧妙地进化着对光的有效捕捉和利用。除了利用光作为生长的能源外，它也是环境信息的重要来源。微生物已经进化出了特别多样化的系统，它们利用光产生能量，避开恶劣的环境，并确定适合营养和生长的环境。生物体将光能转化为化学能用于生长的代谢模式被称为光养（来自希腊语[photo-]，“光”和[trophe]，“营养”）。地球上为光养提供动力的最重要的生物过程是氧气光合作用，它利用含有叶绿素色素的多亚基蛋白质复合物（称为光系统）产生我们呼吸的氧气。这些光系统在捕捉和利用光方面效率很高，但在很大程度上依赖于铁来发挥作用。此外，第二种机制上不同的过程，独立于光系统之外，也可以为光养提供动力，并利用被称为视紫红质的膜内光感受器。视紫红质是由视蛋白膜蛋白组成的分子，它结合视网膜色素，但与光系统不同，它不需要铁来发挥作用。它们的工作原理是基于它们的单一性。紫红质没有使用由多个基因编码的复杂光系统，而是将光吸收和能量保存的任务结合到一个由单个基因编码的单一蛋白质中。吸收光后，视网膜色素的化学结构发生变化，并在分子内引发一系列结构变化。视紫红质光感受器最早是在古代的原核细菌（没有细胞核和膜结合细胞器的细胞）中发现的，但后来也在非常遥远的细菌中发现。海洋环境中高丰度的细菌视紫红质表明基于视紫红质的光养是海洋中一个全球性的重要微生物过程。令人惊讶的是，最近在包括光合作用的海洋浮游植物在内的单细胞真核生物（有细胞核和核包膜包裹遗传物质的生物）中也发现了视紫红质。然而，真核视紫红质在存在更节能的光系统中的功能仍然令人困惑。在初步研究中，我们提供了第一个实验证据，证明在铁限制的浮游植物中，编码视紫红质的基因被高度上调。它们在铁含量有限的海洋中也更为丰富，这些海洋约占全球海洋表面的三分之一。这些发现为我们的研究假设提供了第一个直接证据，即海洋浮游植物中的视紫红质为铁依赖的叶绿素光合作用提供了一种以前未知的备份机制，可以在铁依赖的光系统缺乏铁时提高化学能的产生和生长。这一新机制特别令人感兴趣，因为最近的研究表明，由于人为二氧化碳溶解增加而导致的海洋酸化会降低浮游植物的铁供应，这可能会改变海洋浮游植物的多样性，并有利于在铁浓度降低时具有竞争优势的物种（例如通过视紫红质光合作用）。在我们的研究项目中，我们将使用新的分子遗传学方法来验证我们的研究假设，并进一步探索视紫红质在全球重要的海洋浮游植物中的细胞作用和环境意义。我们的研究结果将为海洋浮游植物如何利用视紫红质提供基本的新见解。这将引起科学界的极大兴趣，因为浮游植物隶属于许多不同的学科，从海洋和气候科学到材料科学和可再生能源。

项目成果

Evolutionary genomics of the cold-adapted diatom Fragilariopsis cylindrus

• DOI: 10.1038/nature20803
• 发表时间: 2017-01-26
• 期刊: NATURE
• 影响因子: 64.8
• 作者: Mock, Thomas;Otillar, Robert P.;Grigoriev, Igor V.
• 通讯作者: Grigoriev, Igor V.

Diatoms glass - dwelling dynamos

硅藻玻璃——住宅发电机

• 发表时间: 2014
• 期刊: Microbiology Today
• 作者: Hopes A.