Transcriptomic landscape of the kleptoplastic sea slug Elysia viridis

Certain sacoglossan sea slugs can sequester and maintain photosynthetically active chloroplasts through algae feeding, a phenomenon called kleptoplasty. The period while these plastids remain active inside the slug's body is species- and environment-dependent and can span from a few days to more than three weeks. Here we report for the first time the transcriptome of sea slug Elysia viridis (Montagu, 1804), which can maintain kleptoplasts for more than two weeks and is distributed along all the Atlantic European coastline. The obtained reference transcriptome consisted of 16,977 protein-coding sequences, corresponding to 10,708 different proteins, and we neither detected any transcripts from the alga nucleus nor any gene ontology related to plastids or photosynthesis. We detected an important activity in the ROS protection mechanisms, which could be involved in the time while E. viridis maintain their kleptoplasts. Our results bring evidence more to leave the horizontal gene transfer theory and reinforce the hypothesis that controlling oxidative stress inside the cells may play a key role in plastids maintenance. ### Competing Interest Statement The authors have declared no competing interest.