CAREER: Comparative Biology of Phagocytosis in Green Algae and Other Protists with Emphasis on its Roles in the Endosymbiotic Origin of Eukaryotic Photosynthesis

真核生物的细胞具有复杂的内部结构，如细胞核和线粒体，与细菌细胞不同。光合作用的真核生物如植物和藻类的细胞具有叶绿体，叶绿体是一种典型地被着色为绿色并且负责从阳光产生细胞能量的细胞器。虽然叶绿体是细胞的一部分，不能在细胞外单独生存，但它起源于一个自由生活的细菌，该细菌被吞噬（即，吞噬作用），并与早期宿主真核生物形成细胞内共生。本研究的目的是表征几个分类上不同的群体，包括绿色藻类的摄食机制。在这些群体中，对喂养的了解尤其少。例如，只有少数绿色藻类仍然有能力消耗食物颗粒。这项研究有可能深入了解细菌的进食过程，最终导致叶绿体作为光合真核生物内的细胞器的进化。这项工作将涉及细胞培养，成像和分子测序工具的组合，并将培训一批年轻的研究人员，包括研究生和本科生暑期实习生。 首席研究员最近在一个绿色藻类谱系中发现了吞噬作用的确切证据，这一群体曾被认为完全失去了这种能力。这项研究将评估绿色藻类以及其他几种真核生物谱系中吞噬作用的分子和细胞基础。推动这项研究的主要问题包括：1）其他“早期”的绿色藻类谱系是否能够摄取细菌？在绿色藻类进化过程中，吞噬作用何时丧失，丧失了多少次？2)资源限制促进兼养绿色藻类的吞噬作用吗？如果是这样的话，这是否为某些绿色藻类提供了足够的进化压力，使它们仍能保持进食能力？3)在绿色藻类和其他原生生物中，哪些基因和蛋白质参与了吞噬作用？吞噬作用的谱系特异性特征是否在真核生物光合作用的起源中发挥了关键作用？该项目将使用多种方法，包括饲养测定、生长实验、荧光和电子显微镜、转录组/基因组测序、吞噬体蛋白质组学和定量PCR。该研究将涉及一名博士后研究员，两名研究生和五名本科实习生的培训。此外，还将通过美国自然历史博物馆研究生课程开发和提供成像技术课程。本课程将训练研究生在比较细胞生物学中使用最新的显微技术。

Eukaryotes are organisms whose cells have complex internal structures, such as nuclei and mitochondria, unlike the cells of bacteria. Cells of photosynthetic eukaryotes such as plants and algae possess a chloroplast, an organelle that is typically colored green and is responsible for generating cellular energy from sunlight. While a chloroplast is part of a cell and cannot live by itself outside of a cell, it originated from a free-living bacterium, which was engulfed (i.e., phagocytosis) by and formed an intracellular symbiosis with an early host eukaryote. This research aims to characterize the feeding mechanism of several taxonomically diverse groups, including green algae. Feeding is especially poorly understood in these groups. Only a few green algae, for example, still have the capacity to consume food particles. The study has the potential to provide insight into the process of feeding on bacteria that eventually led to the evolution of chloroplasts as organelles within photosynthetic eukaryotes. The work will involve a combination of cell culturing, imaging, and molecular sequencing tools, and will train a cohort of young investigators, including graduate students and undergraduate summer interns. The Principal Investigator recently found definitive evidence for phagocytosis in one lineage of green algae, a group that was once considered to have completely lost such capacity. The research will evaluate the molecular and cellular basis of phagocytosis in green algae as well as in several other lineages of eukaryotes. Major questions driving the proposed research include: 1) Are other "early" lineages of green algae capable of ingesting bacteria? When and how many times was phagocytosis lost during green algal evolution?; 2) Does resource limitation facilitate phagocytosis in mixotrophic green algae? If so, could this have provided sufficient evolutionary pressure for some green algae to still retain feeding capacity?; 3) What genes and proteins are involved in phagocytosis in green algae and other protists? Could lineage-specific traits of phagocytosis have played key roles in the origin of eukaryotic photosynthesis? The project will use a combination of methods, including feeding assays, growth experiments, fluorescence and electron microscopy, transcriptome/genome sequencing, phagosome proteomics, and quantitative PCR. The research will involve the training of one postdoctoral researcher, two graduate students, and five undergraduate interns. In addition, a course on imaging techniques will be developed and offered through the American Museum of Natural History graduate program. This course will train graduate students in the use of current microscopic techniques in comparative cell biology.