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

氮同化成氨基酸是调节光合生物生长和生产力的关键过程。氮同化的调控在维管植物和蓝藻中得到了广泛的研究；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。“藻类”一词用于描述光合生物的不同谱系，其中许多是通过独立的次级内共生事件（光合和非光合真核生物之间的共生）产生的。共生体与宿主细胞的结合增加了自然选择作用的遗传多样性，并被认为对现存藻类谱系中观察到的代谢多样性做出了重大贡献。光合谱系的独立内共生起源进一步表明，参与碳和氮代谢的酶可能通过不同的进化过程（例如，基因转移与基因复制）产生，并且在内共生事件之后建立的调控途径可能在谱系之间有所不同。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酶，是碳氮代谢的酶链。多种形式的GS在光合真核生物中表达，同工酶在细胞质或叶绿体中被划分。本研究计划的目标是：(1)通过研究不同藻类谱系中GS的分子进化，扩大我们对光合真核生物氮同化进化的认识；(2)鉴定和表征硅藻骨藻中GS同工酶的生理功能；(3)研究调节骨藻中GS表达的细胞过程。硅藻是一种物种丰富的生物，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了解光合真核生物氮同化的调节机制、藻类生长和海洋生产力的控制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，利用新兴的基因组和生物信息学工具来理解光合生物中耦合碳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，有指导的研究经验可以提高知识生成和获取技能，培养批判性思维技能，并增强各级学习者的自信心。该项目采用多种教学方法，为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了夏季研究机会。该研究联盟为教师提供基于学科的培训，并为K-16年级有效教学实践的讨论提供论坛。此外，PI将开发一门新的基于探究的生理生态学课程，为那些可能没有获得指导研究机会的本科生提供调查和合作学习的经验。综合研究和教学计划表明，PI致力于藻类生理学和进化的多学科研究，创新科学课程的发展和社区教育。

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.