Unity and Diversity of Ultrastructural Systems in Single Celled Eukaryotes

30多亿年来，微生物在丰度和多样性方面一直统治着地球，但微生物的基本和创新特性是所有生物中最不为人所知的。在微生物生命的三个主要谱系（真核生物、细菌和古细菌）中，单细胞真核生物是迄今为止最复杂的，它有细胞核、膜系统、共生获得的细胞器和复杂的细胞骨架，支持大量的细胞扩展和行为。尽管每一个真核微生物只由一个细胞组成，但它本身本质上就是一个宇宙，我们对这些生物的理解的进步推翻了长期以来关于细胞多样性的观点。因此，拟议的研究项目旨在探索这个陌生的世界，以帮助解开生命的总体组成、相互关系和历史。该研究旨在发现和表征单细胞真核生物的新型超微结构系统，并为由数字图像和DNA序列组成的全物种生命百科全书做出贡献。个别项目将跨越真核生物多样性的广泛采样，以解决超微结构特征进化的大规模模式（例如，趋同）。该研究项目将同时继续研究四个主要的单细胞真核生物群体，它们包含了地球上真核生物最不同的三种模式：捕食、光自养和寄生。海洋掠食性鞭毛虫，如真鞭毛虫、甲藻鞭毛虫和冷冻单胞虫，其独立但对应的形态变化模式为研究细胞进化的制约因素和重复创新提供了理想的比较系统。这三个种群都在沙粒之间的空间中多样化，并独立获得了复杂的进食装置、滑翔运动模式、与细菌的共生关系和光合细胞器。拟议的研究计划还将涉及第四组真核生物，这些真核生物为生命史上最神秘的进化转变之一提供了令人信服的见解：从自由生活的光自养祖先的专性细胞内寄生虫的起源。顶复合体与自由生活的鞭毛藻密切相关，尽管作为人类和牲畜的病原体（如疟原虫）而臭名昭著，但大多数顶复合体的多样性在世界海洋中蓬勃发展。顶复合体的起源和多样化将通过探索海洋绿虫的比较超微结构和分子系统发育来解决，绿虫是一种大型的、动态的单细胞寄生虫，感染海洋无脊椎动物宿主。对单细胞真核生物多样性的研究本质上是探索性的，分五个阶段进行：(1)发现、分离和培养来自自然界的生物（例如，班菲尔德海洋科学中心和太平洋其他地区）；(2)利用光镜、荧光共聚焦显微镜和电子显微镜对微生物进行鉴定和超微结构表征；(3)生物的分子特性；(4)与图像处理、下一代测序和分子系统发育相关的计算分析；(5)采用比较法进行进化综合。拟议的研究计划将加速发现来自不同环境的真核细胞的新谱系，扩展和完善理解真核生物多样性的整体系统发育框架，并确定这些生物解决基本生物学问题（例如，细胞运动，进食和光接受）的非常规方法。

For over 3 billion years, microbes have dominate the planet in terms of abundance and diversity, yet the fundamental and innovative properties of microbes are the least understood of all organisms. Of the three major lineages of microbial life (Eukarya, Bacteria and Archaea), single-celled eukaryotes are by far the most complex, having nuclei, endomembrane systems, symbiotically acquired organelles and elaborate cytoskeletons supporting a vast array of cell extensions and behaviors. Despite being composed of only a single cell, each microbial eukaryote is essentially a universe in and of itself, and advances in our understanding of these organisms have overturned long-held views about the diversity of cells. Accordingly, the proposed research program is designed to explore this foreign world in order to help unravel the total composition, interrelationships and history of life. The research aims to discover and characterize novel ultrastructural systems in single-celled eukaryotes and make contributions to an all-species Encyclopedia of Life, consisting of digital images and DNA sequences. Individual projects will span a broad sampling of eukaryotic diversity in order to resolve large-scale patterns of ultrastructural trait evolution (e.g., convergence). The research program will continue to study, in parallel, four major groups of single-celled eukaryotes that encompass what are arguably the three most dissimilar modes of eukaryotic life on the planet: predation, photoautotrophy, and parasitism. The independent but corresponding patterns of morphological change in marine predatory flagellates, such as euglenids, dinoflagellates and cryomonads, represent an ideal comparative system for investigating the constraints and reoccurring innovations in cell evolution. All three groups have diversified within the spaces between grains of sand and have independently acquired sophisticated feeding apparatuses, modes of gliding locomotion, symbiotic associations with bacteria, and photosynthetic organelles. The proposed research program will also address a fourth group of eukaryotes that provides compelling insights into one of the most enigmatic evolutionary transformations in the history of life: the origin of obligate intracellular parasites from free-living, photoautotrophic ancestors. Apicomplexans are closely related to free-living dinoflagellates, and despite being infamous as pathogens of humans and livestock (e.g., Plasmodium), most of apicomplexan diversity is thriving in the world’s oceans. The origin and diversification of apicomplexans will be addressed by exploring the comparative ultrastructure and molecular phylogeny of marine gregarines, which are large and dynamic single-celled parasites that infect marine invertebrate hosts. Research on the diversity of single-celled eukaryotes is, in essence, exploratory and progresses in five phases: (1) discovery, isolation and cultivation of the organisms from nature (e.g., Bamfield Marine Sciences Centre and other regions of the Pacific Ocean); (2) identification and ultrastructural characterization of the organisms using light, fluorescence confocal and electron microscopy; (3) molecular characterization of the organisms; (4) computational analyses associated with image processing, next-generation sequencing and molecular phylogenetics; and (5) evolutionary synthesis using comparative methods. The proposed research program will accelerate the discovery of new lineages of eukaryotic cells from diverse environments, expand and refine the overall phylogenetic framework for understanding eukaryotic diversity, and identify unconventional ways in which these organisms have solved basic biological problems (e.g., cell locomotion, feeding, and photoreception).