An Examination of the Autocatalytic Cell Death Machinery in Marine, Planktonic Photoautotrophs

浮游植物的死亡率在很大程度上决定了其他生物的生存方式，对于连接海洋中的主要生物地球化学循环至关重要。 不幸的是，控制自然系统中开花急剧和突然终止的机制还没有很好的理解。像所有海洋生物一样，微观浮游植物在海洋中遇到不利的环境条件（即，营养胁迫），其导致生理胁迫，有时导致死亡。 事实上，大量的细胞死亡（通过溶解）已经在实地研究中记录，一些估计超过50%的浮游植物生长。 该提案研究了海洋浮游植物中的自催化细胞死亡，这是一种类似于多细胞生物中的程序性细胞死亡（PCD）或凋亡的自我毁灭。它侧重于（1）PCD作为浮游植物对环境压力的一种关键死亡机制的生态相关性，以及（2）海洋浮游植物中PCD的起源，通过检查其细胞机制及其与多细胞生物所使用的机制的关系，对这种类型的死亡有最好的理解。 拟议的研究探讨PCD途径在不同谱系的浮游植物，包括蓝藻（Trichodesmium sp. IMS 101），绿藻（杜氏盐藻tertiolecta）和球石藻（Emiliania huxleyi）。基于初步发现，类似的PCD途径似乎在这些生物体中响应于生理和环境应激（培养年龄、氧化应激、铁和磷限制）而被激活，每一种都导致大量细胞死亡。 它具体解决了一类特定的蛋白酶，称为半胱天冬酶，激活和执行浮游植物的PCD。 半胱天冬酶在后生动物PCD的执行中起着普遍的作用，在细胞解体（效应器）和启动这种解体（启动器）中起作用。 此外，本研究还利用E. huxleyi及其病毒（EhV 1）作为模型系统。 在后生动物（例如，人类），PCD通常被宿主细胞用作防御机制以防止病毒感染的传播。PCD机制可能已经在浮游植物中进化，以防止大规模的病毒感染和自然种群的死亡。 研究结果将为浮游植物死亡率以及PCD的新生态和进化背景提供关键的机制见解。 研究活动将为本科生的发展提供实践培训，并有助于扩大妇女和少数族裔等代表性不足群体的参与。 它还将建立罗格斯大学，一个领先的研究机构，和加州州立大学圣马科斯大学，一个新的少数民族服务机构与强大的教育使命之间的合作。 与海洋和沿海科学研究所（罗格斯大学）的教育工作人员合作，研究结果将被翻译为K-12和新泽西的公众受众，作为新成立的NSF资助的大西洋中部海洋科学教育卓越中心（MA-COSEE）的一部分。

Phytoplankton mortality largely determines how other organisms live and is essential to linking major biogeochemical cycles in the ocean. Unfortunately, the mechanisms controlling the dramatic and abrupt bloom termination in natural systems are not well understood. Like all marine organisms, microscopic phytoplankton encounter adverse environmental conditions in the ocean (i.e., nutrient stress), which result in physiological stress and, sometimes, death. Indeed, substantial cell death (via lysis) has been documented in field studies with some estimates exceeding 50% of phytoplankton growth. This proposal examines autocatalyzed cell death in marine phytoplankton, a self-destruction analogous to programmed cell death (PCD) or apoptosis in multicellular organisms. It focuses (1) on the ecological relevance of PCD as a critical mortality mechanism of phytoplankton in response to environmental stress and (2) on the origins of PCD in marine phytoplankton by examining its cellular machinery and their relationship to those employed by multicellular organisms, for which this type of death in best understood. Proposed research examines PCD pathways in diverse lineages of phytoplankton, including a cyanobacterium (Trichodesmium sp. IMS101), a chlorophyte (Dunaliella tertiolecta) and a coccolithophorid (Emiliania huxleyi). Based on preliminary findings, similar PCD pathways appear to be activated in these organisms in response to physiological and environmental stress (culture age, oxidative stress, iron and phosphorus limitation), each resulting in massive cell death. It specifically addresses whether a specific class of proteases, termed Caspases, activate and execute PCD in phytoplankton. Caspases play a ubiquitous role in the execution of PCD in metazoans, functioning both in cell disassembly (effectors) and in initiating this disassembly (initiators). In addition, this proposal investigates whether the PCD cellular machinery is activated upon viral infection of phytoplankton, using E. huxleyi and its virus (EhV1) as a model system. In metazoans (e.g., humans), PCD is often employed as a defense mechanism by host cells to prevent spread of viral infection. The PCD machinery may have evolved in phytoplankton to prevent massive viral infection and demise of natural populations.This research will provide a variety of broader impacts. Research findings will provide critical mechanistic insight into phytoplankton mortality as well as novel ecological and evolutionary context for PCD. Research activities will provide hands-on training for development of an undergraduate student and help to broaden the participation of underrepresented groups such as women and minorities. It will also establish collaboration between Rutgers, a leading research institute, and Cal State University San Marcos, a new minority serving institution with a strong educational mission. In collaboration with the education staff at the Institute of Marine and Coastal Science (Rutgers University), research findings will be translated for K-12 and public audiences in New Jersey, as part of the newly established, NSF-funded Mid-Atlantic Center for Ocean Science Education Excellence (MA-COSEE).