CAREER: Nitrogen Assimilation in Marine Algae: Evolution, Physiology, and Educational Opportunties

氮同化为氨基酸是调节光合作用生物生长和生产力的关键过程。在维管束植物和蓝藻中，氮同化的调控已经被广泛研究，然而，关于这些途径在真核藻类中的进化和调控的信息有限。术语“藻类”用于描述光合作用有机体的不同谱系，其中许多是通过独立的次生内共生事件(光合作用和非光合作用真核生物之间的共生)产生的。在宿主细胞中加入共生体增加了自然选择可以作用的遗传多样性，并被认为对在现有藻类谱系中观察到的代谢多样性做出了重大贡献。光合作用谱系的独立内共生起源进一步表明，参与碳氮代谢的酶可能是通过不同的进化过程(如基因转移和基因复制)而产生的，并且在内共生事件之后建立的调控途径在不同的品系之间可能是不同的。谷氨酰胺合成酶(GS)是所有生物体中氨同化和谷氨酰胺生物合成所必需的，是碳和氮代谢之间的酶纽带。在光合作用的真核生物中表达多种形式的GS，同工酶在细胞质或叶绿体中被分割。本研究的目标是(1)通过研究不同藻类中GS的分子进化，扩大我们对光合作用真核生物氮同化进化的认识；(2)鉴定和表征中肋骨条藻GS同工酶的生理功能；(3)研究中肋骨条藻GS表达的调控细胞过程。硅藻是一类物种丰富的生物，对海洋初级生产力和全球生物地球化学循环有重要贡献。这项研究将有助于我们理解光合作用真核生物氮同化的调控机制，控制藻类生长和海洋生产力的过程，以及代谢途径的进化。这项工作将为未来的研究提供一个框架，使用新兴的基因组和生物信息学工具来了解光合作用生物中耦合碳和氮代谢的复杂和相互作用的途径。贯穿整个项目的共同主线是，有指导的研究经验提高了知识生成和获取技能，培养了批判性思维能力，并增加了各级学习者的自信心。该项目使用几种教学方法，为来自当地公立学校的本科生、研究生和科学教师提供参与研究性学习活动的新机会。作为克拉克大学与伍斯特社区建立伙伴关系的使命的一部分，该项目为初中和高中科学教师提供暑期研究机会。该研究联盟为教师提供以学科为基础的培训，并为讨论K-16年级的有效教学实践提供了一个论坛。此外，PI将开发一门新的生理生态学探究式课程，为可能没有寻求指导研究机会的本科生提供调查和合作学习体验。综合的研究和教学计划表明，该协会致力于致力于藻类生理学和进化的多学科研究，开发创新的科学课程，并致力于社区教育。

The assimilation of nitrogen into amino acids is a key process regulating the growth and productivity of photosynthetic organisms. The regulation of nitrogen assimilation has been studied extensively in vascular plants and cyanobacteria; however, only limited information is available concerning the evolution and regulation of these pathways in eukaryotic algae. The term "algae" is used to describe diverse lineages of photosynthetic organisms, many of which arose through independent secondary endosymbiotic events (symbioses between photosynthetic and non-photosynthetic eukaryotes). The incorporation of symbionts into host cells increased the genetic diversity on which natural selection could act and is assumed to have contributed significantly to the metabolic diversity observed in extant algal lineages. The independent endosymbiotic origin of photosynthetic lineages further suggests that enzymes involved in carbon and nitrogen metabolism may have arisen through different evolutionary processes (e.g., gene transfer versus gene duplication) and that regulatory pathways, which were established following the endosymbiotic events, may differ among lineages.The enzyme glutamine synthetase (GS) is essential for ammonium assimilation and glutamine biosynthesis in all organisms and is the enzymatic link between carbon and nitrogen metabolism. Multiple forms of GS are expressed in photosynthetic eukaryotes and the isoenzymes are compartmentalized in either the cytosol or chloroplast. The goals of this research program are to (1) expand our knowledge of the evolution of nitrogen assimilation in photosynthetic eukaryotes by examining the molecular evolution of GS in diverse algae lineages, (2) identify and characterize the physiological functions of GS isoenzymes in the diatom Skeletonema costatum, and (3) to examine the cellular processes that regulate GS expression in S. costatum. Diatoms are a species-rich group of organisms that contribute significantly to oceanic primary productivity and global biogeochemical cycles. This research will contribute to our understanding of mechanisms regulating nitrogen assimilation in photosynthetic eukaryotes, processes governing algal growth and oceanic productivity, and the evolution of metabolic pathways. The work will provide a framework for future studies using emerging genomic and bioinformatic tools to understand the complex and interacting pathways coupling carbon and nitrogen metabolism in photosynthetic organisms. The common thread woven throughout this project is that mentored research experiences improve knowledge generation and acquisition skills, develop critical thinking skills, and increase self-confidence in learners at all levels. This project uses several pedagogical approaches to provide new opportunities for undergraduates, graduate students, and science teachers from local public schools to participate in research-based learning activities. As part of Clark University's mission to establish partnerships with the Worcester community, this project provides summer research opportunities for middle- and high-school science teachers. This research alliance provides discipline-based training for teachers and a forum for the discussion of effective teaching practices for grades K-16. In addition, the PI will develop a new inquiry-based course in physiological ecology that offers investigative and cooperative learning experiences to undergraduates who may not have pursed mentored research opportunities. The integrated research and teaching program illustrates the PI's commitment to a career aimed at the multi-disciplinary study of algal physiology and evolution, to the development of innovative science curricula, and to community education.