The Spirogyra genome and the origin of that spiral chloroplast

I expect we’ve all been captivated by images of the beautiful spiral chloroplasts in the Spirogyra genus of filamentous algae, and who could forget that name? A new paper by Goldbecker et al. presents the genome of Spirogyra pratensis, uncovering not only some insights into this remarkable structure, but also many the unique and unexpected  insights into this close relative of land plants. Spirogyra are members of the Zygnematophytes, which diverged from land plants about 600 million years ago (quite recently, really). The authors found that the Spirogyra genome is very small, probably due to genome reduction and gene loss. Unlike other algae and plants, the chloroplast does not move upon high-light stress, and there’s an interesting discussion about how the spiral forms and is maintained. The authors also carried out transcriptomic studies of developmental stages and responses to light, and take a deeper dive into several gene families involved in stress responses, cell wall formation, cell and plastid division, and others. It’s a comprehensive look into this charismatic species. (Summary by Mary Williams @PlantTeaching.bsky.org) bioRxiv https://doi.org/10.1101/2025.10.09.681428