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，既展示了真核细胞的非凡复杂性，又帮助我们更好地理解叶绿体是如何在生命之树中传播的。该项目产生的研究将揭示单细胞生物维持这种细胞复杂性的适应性，这种单细胞生物已经从居住在池塘，河口和沉积物表面栖息地的祖先中分化出来，成为世界沿海海洋中具有广泛生态作用的主要光合浮游物种。这种转变由于其不稳定性而更加引人注目——它的细胞和代谢复杂性以及光合作用能力是窃取和重新利用其藻类猎物的细胞部分和基因的结果。这项研究将确定这个过程是如何发生的，从而揭示一些重要的，但神秘的进化过程。该项目将帮助培养两名博士后科学家，为他们从事科学研究的职业生涯做好准备。该项目还将在实验室培训本科生，并将与Zephyr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，包括在科学领域代表性明显不足的地区。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，与公众互动，帮助公众了解海洋“看不见的”（即微观的）生物多样性。该项目将比较一种纤毛虫属的细胞、代谢和遗传适应性，这些纤毛虫跨越了从异养到光养的功能营养模式，通过连续的混合营养模式。在变色龙中，混合营养是由细胞器偷窃（或盗贼成形术）驱动的，这在变色龙中均匀地支持其在进食和光合作用之间的营养和能量需求。然而，在M. rubrum中，它更多的是一种窃取细胞器的手段，包括猎物的活动核，以充分利用猎物的光合代谢。了解红分枝杆菌是如何适应完全依赖窃取的细胞器和它们的新陈代谢来生存的，是这个项目的主要目标之一。该项目将使用比较组学的方法对这两个物种和异养物种M. pulex进行比较，以阐明遗传和代谢的适应和创新。该项目还将使用空间蛋白质组学和免疫化学来了解红毛分枝杆菌中被盗细胞核的蛋白质是如何转运到叶绿体的，尽管它们在新宿主中进行了大规模的重组和失去了内膜的连续性。同样的技术也将寻求了解纤毛虫基因可能有助于维持和控制被盗的细胞器，并促进其代谢的利用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.