Role of the Diatom Mitochondria in Cellular Nitrogen Metabolism

硅藻线粒体在细胞氮代谢中的作用

• 批准号: 1024913
• 负责人: Andrew Allen
• 金额: $ 111.91万
• 依托单位: J. Craig Venter Institute, Inc.
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-15 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1024913&HistoricalAwards=false
• 关键词: Role; Diatom; Mitochondria; Cellular; Nitrogen

Current estimates indicate that approximately half of the annual photosynthetic production of organic matter on Earth takes place in the euphotic zone of the water column in marine environments, making the ocean a major component of the global carbon cycle. Nearly all of the bloom-forming phytoplankton in the modern ocean, including the diatoms, are members of the chlorophyll c (Chl c) lineage. It is now well accepted that chlorophyll c-containing algae share a common ancestry where a eukaryote enveloped and domesticated a red algae, incorporating biochemical entities from both organisms. The subsequent diversification of this lineage has yielded an astounding diversity of ecologically dominant phytoplankton. Ultimately carbon export in marine ecosystems is governed and balanced by assimilation of nitrogen by phytoplankton. Among marine phytoplankton, diatoms are often the most responsive to mixing events where nutrient laden water is injected into the sunlit euphotic zone, yet the cellular basis for this competitive advantage is poorly understood. The global state-of-knowledge concerning nitrogen metabolism in photosynthetic eukaryotes is largely based on biochemistry and genome sequence data from a few well-studied model green algae and vascular plants. Genome sequences, physiological and biochemical studies, and gene and protein expression data indicate that diatoms and other Chl c algae utilize a variety of biochemical components previously only observed in metazoans or bacteria. A complete metazoan-like urea cycle, for example, appears to function in concert with genes of bacterial and red or green algal origin in a functionally expanded and heretofore unobserved fashion. In metazoans the urea cycle has a function related to cellular detoxification and export of fixed nitrogen. The presence of the urea degrading enzyme urease strongly suggests an alternative function in diatoms.This research is addressing the hypothesis that in marine diatoms, which are frequently subjected to nitrogen limitation, the urea cycle and associated mitochondrial enzymes function as an inorganic carbon and nitrogen recycling and repackaging hub; ultimately serving to redistribute catabolically derived NH4+ to arginine and other non-amino-acid nitrogen compounds. Based on recent advancements in diatom reverse genetics and other recently developed resources for genome enabled research, basic hypothesis concerning the role of mitochondria in nitrogen assimilation and metabolism in marine diatoms is being evaluated.Broader ImpactsAnthropogenic coastal loading of organic and inorganic nitrogen is expected to increase and climate change-induced shifts in oceanic mixed layer depth and mixing frequency are predicted to alter the delivery of nutrients into the euphotic zone. As a result, a key research focus is to facilitate prediction of how diatoms and other Chl c algae will respond to changing frequency and intensity of nutrient delivery events. This research will contribute to a more accurate depiction of nitrogen metabolism in marine algae, which is critically important for predictive ecosystem modeling.As part of the research project, a high school biology teacher from the Escondido Union High School District in San Diego will be recruited to work on a specific topic related to the proposed research. Upon completion of his/her paid internship, in collaboration with the PIs, the teacher will design a classroom activity and curriculum installment related to the rapidly emerging field of marine genomics, also including associated topics in marine biogeochemistry, for use the following school year.

目前的估计表明，地球上每年大约一半的有机物光合作用产生发生在海洋环境中水柱的光区，使海洋成为全球碳循环的主要组成部分。在现代海洋中，几乎所有形成水华的浮游植物，包括硅藻，都是叶绿素c （Chl c）谱系的成员。现在人们普遍认为，含叶绿素c的藻类具有共同的祖先，真核生物包裹并驯化了红藻，结合了两种生物的生化实体。这个谱系随后的多样化产生了令人震惊的生态优势浮游植物的多样性。最终，海洋生态系统中的碳输出是由浮游植物对氮的同化来控制和平衡的。在海洋浮游植物中，硅藻通常对富含营养物质的水注入阳光照射的光区最敏感，然而这种竞争优势的细胞基础尚不清楚。关于光合真核生物氮代谢的全球知识状况主要基于生物化学和基因组序列数据，这些数据来自一些已经得到充分研究的模式绿藻和维管植物。基因组序列、生理生化研究以及基因和蛋白质表达数据表明，硅藻和其他Chl - c藻类利用了多种以前仅在后生动物或细菌中观察到的生化成分。例如，一个完整的类似后生动物的尿素循环，似乎以一种功能扩展且迄今未被观察到的方式，与细菌和红藻或绿藻的基因协同工作。在后生动物中，尿素循环具有与细胞解毒和输出固定氮有关的功能。尿素降解酶脲酶的存在强烈暗示了硅藻的另一种功能。本研究解决了这样一个假设：在经常受到氮限制的海洋硅藻中，尿素循环和相关的线粒体酶作为无机碳和氮的回收和再包装中心；最终将分解代谢产生的NH4+重新分配给精氨酸和其他非氨基酸氮化合物。基于硅藻反向遗传学的最新进展和其他基因组化研究的最新进展，本文对线粒体在海洋硅藻氮同化和代谢中的作用的基本假设进行了评价。更广泛的影响：沿海的人为有机氮和无机氮负荷预计将增加，气候变化引起的海洋混合层深度和混合频率的变化预计将改变营养物向高光带的输送。因此，一个关键的研究重点是促进预测硅藻和其他Chl - c藻类如何响应不断变化的养分输送事件的频率和强度。这项研究将有助于更准确地描述海洋藻类的氮代谢，这对预测生态系统建模至关重要。作为研究项目的一部分，圣地亚哥埃斯孔迪多联合高中学区的一名高中生物教师将被招募来研究与拟议研究相关的特定主题。在完成带薪实习后，教师将与pi合作，设计与快速发展的海洋基因组学领域相关的课堂活动和课程，也包括海洋生物地球化学的相关主题，以供下一学年使用。