Collaborative Research: Evolution of acquired phototrophy by organelle sequestration in Mesodinium ciliates

这个项目为进化过程提供了一个独特的视角，展示了真核细胞的非凡复杂性，并帮助我们更好地了解叶绿体是如何在生命树上传播的。该项目产生的研究将揭示在单细胞生物体中保持这种细胞复杂性的适应性，单细胞生物体已经从栖息在池塘、河口和沉积物表面生境的祖先中分化出来，成为世界沿海海洋中具有广泛生态作用的主要光合作用浮游物种。这种转变因其不稳定而更加引人注目--其细胞和新陈代谢的复杂性以及光合作用能力是窃取和改变其藻类猎物的细胞部分和基因的用途的结果。这项研究将确定这一过程是如何发生的，从而为重要而神秘的进化过程提供一些线索。该项目将帮助培养两名博士后科学家，并为他们在科学研究领域的专业生涯做好准备。该项目还将在实验室培训本科生，并将与泽菲尔基金会合作，该基金会是一个海洋科学素养和教育项目，为地区学校(6-12级)提供服务，包括在科学领域主要代表不足的群体的学区。该项目还将与圣巴巴拉自然历史博物馆的水下公园日合作，与公众合作，帮助公众了解海洋的“看不见”(即微小的)生物多样性。该项目将比较一类纤毛虫的细胞、代谢和遗传适应情况，这些纤毛虫跨越功能营养模式的异养和光营养，通过混合营养的连续体。中草藻的混合营养是由细胞器窃取(或klepeplit)驱动的，它在取食和光合作用之间均匀地支持其营养和能量需求。然而，在红色分枝杆菌中，它更多的是一种窃取细胞器的手段，包括其猎物的活跃核，以充分利用其猎物的光合代谢。了解红色分枝杆菌如何适应完全依靠偷来的细胞器及其新陈代谢生存，是该项目的主要目标之一。该项目将使用这两个物种和异养菌M.Pulex之间的比较组学方法来阐明遗传和新陈代谢的适应和创新。该项目还将使用空间蛋白质组学和免疫化学，以了解蛋白质如何从被盗的细胞核转移到叶绿体，尽管它们的新宿主发生了大规模重组和内膜连续性的丧失。同样的技术还将寻求了解纤毛虫基因可能有助于维护和控制被盗细胞器并促进其新陈代谢的利用。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project offers a unique perspective into evolutionary processes that showcase both the extraordinary complexity of eukaryotic cells and help us to better understand how chloroplasts have spread around the tree of life. Research generated by this project will reveal adaptations for maintaining this cellular complexity in a unicellular organism, which has diverged from ancestors inhabiting ponds, estuaries, and sediment surface habitats, to become a major photosynthetic planktonic species in the world’s coastal oceans with wide reaching ecological roles. This transition is even more remarkable due its precariousness - its cellular and metabolic complexity and photosynthetic capabilities are the result of stealing and repurposing cell parts and genes of its algal prey. This research will determine how this process happens, and thereby shed some light on important, yet enigmatic, evolutionary processes. The project will help to train two postdoctoral scientists and prepare them for a professional career in scientific research. The project will also train undergraduate students in the laboratory, and will engage with the Zephyr Foundation, a marine science literacy and education program, which serves regional schools (levels 6-12), including districts with predominantly underrepresented groups in sciences. The project will also engage with the public in a collaboration with the Santa Barbara Museum of Natural History’s Underwater Parks Day to help educate the public about the oceans’ “invisible” (i.e., microscopic) biodiversity. The project will compare cellular, metabolic, and genetic adaptations across a genus of ciliates that span functional nutritional modes of heterotrophy to phototrophy, through a continuum of mixotrophy. Mixotrophy in Mesodinium is driven by organelle stealing (or kleptoplasty), which in M. chamaeleon evenly supports its nutritional and energy needs between feeding and photosynthesis. However, in M. rubrum it is more a means to steal organelles, including the active nucleus of its prey, to fully exploit its prey’s photosynthetic metabolism. Understanding how M. rubrum has adapted to be fully reliant on stolen organelles and their metabolism for its survival is one of the main objectives of this project. The project will use comparative omics approaches between these two species and the heterotroph, M. pulex, to illuminate genetic and metabolic adaptations and innovations. The project will also use spatial proteomics and immunochemistry, to understand how proteins from the stolen nucleus in M. rubrum transit to the chloroplasts, despite massive reorganization and loss of endomembrane continuity in their new host. The same techniques will also seek to understand what ciliate genes may be contributing to maintaining and controlling stolen organelles and facilitating exploitation of their metabolism.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.