KleptoSphere: External and internal plastid transformations during the chloroplast–kleptoplast transition in photosynthetic sea slugs

Application summary

Kleptoplastic sea slugs steal chloroplasts (plastids) from algae and maintain the plastids as photosynthetic organelles, kleptoplasts, inside their own cells for months without any help from the algal nucleus. This should not be possible, as plastids are damaged in light due to the strong redox chemistry of photosynthesis, and the repair requires nuclear-encoded proteins in algae and plants. KleptoSphere will reveal the molecular mechanisms used by the slugs to maintain their kleptoplasts functional, that have so far remained a mystery. The project addresses three major unknowns: when and how kleptoplasts acquire their highly spherical shape, which beneficial structural and protein-level changes occur in the plastid/kleptoplast membranes upon incorporation by the slugs, and whether animal proteins contribute to kleptoplast longevity directly. By combining ultrastructural imaging, proteomics, and photosynthesis measurements, the KleptoSphere project will (1) pinpoint the timing and mechanisms of plastid shape change inside the slugs, (2) reveal plastid-to-kleptoplast protein and envelope/thylakoid membrane alterations, and (3) identify animal-derived proteins supporting oxidative stress tolerance of the kleptoplasts. The results will generate a comprehensive roadmap outlining how kleptoplasts remain functional in sea slugs, offering insights into kleptoplast biology and symbiosis in marine environments.