The genome of a hadal sea cucumber reveals novel adaptive strategies to deep-sea environments.

How organisms cope with coldness and high pressure in the hadal zone remains poorly understood Here, we sequenced and assembled the genome of hadal sea cucumber sp. Yap with high quality and explored its potential mechanisms for deep-sea adaptation. First, the expansion of for rate-limiting enzyme in the DHA synthesis pathway, increased DHA content in the phospholipid bilayer, and positive selection of may maintain cell membrane fluidity. Second, three genes for translation initiation factors and two for ribosomal proteins underwent expansion, and three ribosomal protein genes were positively selected, which may ameliorate the protein synthesis inhibition or ribosome dissociation in the hadal zone. Third, expansion and positive selection of genes associated with stalled replication fork recovery and DNA repair suggest improvements in DNA protection. This is the first genome sequence of a hadal invertebrate. Our results provide insights into the genetic adaptations used by invertebrate in deep oceans.