Collaborative Research: PurSUiT: Phylogenomics and taxonomic revision of Rhopalodiales - diatoms with obligate cyanobacterial endosymbionts

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Symbiosis, the close association of distinct organisms living together, is a common phenomenon in nature. From the ancient organelles inside human cells, to lichens and corals, the integration of life forms from disparate backgrounds occurs across the tree of life. What are the mechanisms that drive this integration to happen? What are the costs and benefits of these relationships? In one group of eukaryotic microorganisms called diatoms (which form the base of the food chain in aquatic ecosystems and generate more oxygen by photosynthesis than all rainforests combined), symbioses are commonly formed with cyanobacteria that “fix” nitrogen. This project will analyze how these organisms came together; whether that happened once or many times; the impacts of the association on host, symbiont and the ecosystems in which they live; and how the co-occurring organisms coordinate their life activities. Over 40 students will be involved in the research through courses, workshops, and research training. The project will be featured in the Hidden World of Microbial Diversity course offered through the University of Montana’s Indigenous Research and STEM Education summer program.A scientific collaboration between three U.S. universities and seven universities, research institutes and museums in China, India, Indonesia and Argentina will gather data from a variety of sources, including entire genomes of the chloroplast and mitochondria of the diatom hosts, cell wall morphology of the diatoms, and the entire genome of the cyanobacterial symbiont (also called a spheroid body) to address three main aims: 1) the evolutionary origins and diversification of the diatom order Rhopalodiales, including when the endosymbiont was acquired during diversification of this lineage; 2) the sister taxon of the Rhopalodiales, and the extent of cryptic diversity among cosmopolitan rhopalodian taxa; 3) the coevolution of host and symbiont. The project will integrate information on the group from herbarium collections in the United States, Europe and South America for both extant and fossil taxa. Integrated phylogenetics, functional genomics and taxonomic revisionary work will produce a time-calibrated phylogeny that will inform a revised classification system for the group.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.