Uranium (U) is an actinide element that is naturally present in rocks and soils at an average concentration of 3 ppm. The main sources of anthropogenic U contamination in the environment are associated with the nuclear industry and agricultural practices, particularly the use of mineral phosphate fertilizers that are often significantly enriched in U and other hazardous elements. Uranium is a non-essential element that is weakly radioactive in its natural form but chemically toxic to all organisms. It can be taken up from the environment by photosynthetic organisms, where it disrupts several biological processes (mineral homeostasis, metabolism, hormonal regulation…), ultimately inhibiting growth. In recent years, significant progress has been made in understanding the phytotoxicity of U. In particular, we showed that U uptake in plants is mediated primarily by calcium-permeable cation channels (Sarthou 2022), a pathway that is also operating in yeast cells (Revel 2022) and potentially other eukaryotes. In roots, U triggers a complex reorganization of the cell wall and Casparian strips and regulates the abundance of several metal-binding proteins that could mediate its toxicity or contribute to its chelation (Przybyla-Toscano 2025). Two uranium-binding proteins from Arabidopsis were characterized at the biochemical and structural levels (Vallet 2024; Revel 2025). We also characterized a unicellular green microalga of the Coelastrella genus that is hypertolerant to U (Beaulier 2024). The alga has the ability to accumulate remarkably high amount of U, with up to 240 mg tightly bound U per g of dry biomass. Also, it is a very promising organism for the bioremediation of polluted environments, being capable of an efficient capture of U or lead from contaminated natural waters, while producing biomass enriched in lipids. In this presentation, the cellular and molecular responses of Coelastrella to U stress will be described. By combining cellular imaging approaches with RNAseq analysis, we identified the subcellular compartments contributing to U sequestration, characterized the main processes perturbed by the metal, and pinpointed candidate molecular actors (transporters and metal-binding proteins) potentially involved in its uptake, efflux, and chelation.