Plastid longevity in sacoglossan sea slugs

• Applicant: Professor Dr. Sven B. Gould
• Subject Area: Evolutionary Cell and Developmental Biology (Zoology) ; Animal Physiology and Biochemistry ; Plant Physiology
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 255999527

The endosymbiotic origin of plastids gave rise to heritable photosynthesis in eukaryotes. It entailed the uptake and stable integration of an ancient cyanobacterium by a heterotrophic host. But there are cases where photosynthesis occurs in eukaryotes via symbiotic associations that are not heritable. Sacoglossan sea slugs inhabit marine coastal waters and feed upon algae. Some species feed indiscriminately and digest the algae, others however are selective about their food source and sequester only the plastids, which they then retain in a photosynthetically active state for months to come (kleptoplasts). Notably, such kleptoplasts remain photosynthetically active in the cytosol of slug digestive cells that are devoid of algal nuclei. Because photosynthesis in higher plant plastids strictly depends upon nuclear-encoded gene products, it was long thought that slugs obtained genes from their algal food through lateral gene transfer (LGT) so as to underpin plastid longevity. But recent published reports (starting with our own) refute the LGT hypothesis. In new preliminary work, we have uncovered what we now believe to be the key - overlooked for decades - to understanding sacoclossan kleptoplasty: The plastids remain active, but the slugs are not autotrophic. They survive equally long in light vs. dark. That opens up two very new questions: (i) what benefit do slugs reap from kleptoplasts, which we now think are a food reserve, and (ii) what are the slugs and kleptoplasts contributions to maintaining kleptoplasts photosynthetically active for months of separation from algal nuclear genes.

• DFG Programme: Research Grants
• Participating Persons: Professor Jörg Nickelsen, Ph.D.; Professorin Dr. Heike Wägele