
==== Front
bioRxiv
BIORXIV
bioRxiv
2692-8205
Cold Spring Harbor Laboratory

10.1101/2024.08.27.609708
preprint
1
Article
Genomes of nitrogen-fixing eukaryotes reveal a non-canonical model of organellogenesis
Frail Sarah http://orcid.org/0000-0003-0718-3092

Steele-Ogus Melissa http://orcid.org/0000-0001-8143-1352

Doenier Jon http://orcid.org/0009-0009-4576-0082

Moulin Solène L.Y. http://orcid.org/0000-0002-7347-1247

Braukmann Tom http://orcid.org/0000-0002-2452-3776

Xu Shouling http://orcid.org/0000-0002-6741-9506

Yeh Ellen http://orcid.org/0000-0003-3974-3816

27 8 2024
2024.08.27.609708https://creativecommons.org/licenses/by-nc/4.0/ This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, which allows reusers to distribute, remix, adapt, and build upon the material in any medium or format for noncommercial purposes only, and only so long as attribution is given to the creator.
http://biorxiv.org/lookup/doi/10.1101/2024.08.27.609708
nihpp-2024.08.27.609708.pdf
SUMMARY

Endosymbiont gene transfer and import of host-encoded proteins are considered hallmarks of organelles necessary for stable integration of two cells. However, newer endosymbiotic models have challenged the origin and timing of such genetic integration during organellogenesis. Epithemia diatoms contain diazoplasts, closely related to recently-described nitrogen-fixing organelles, that are also stably integrated and co-speciating with their host algae. We report genomic analyses of two species, freshwater E.clementina and marine E.pelagica , which are highly divergent but share a common endosymbiotic origin. We found minimal evidence of genetic integration: nonfunctional diazoplast-to-nuclear DNA transfers in the E.clementina genome and 6 host-encoded proteins of unknown function in the E.clementina diazoplast proteome, far fewer than in other recently-acquired organelles. Epithemia diazoplasts are a valuable counterpoint to existing organellogenesis models, demonstrating that endosymbionts can be stably integrated and inherited absent significant genetic integration. The minimal genetic integration makes diazoplasts valuable blueprints for bioengineering endosymbiotic compartments de novo .
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pmc
