The chromosome-level genome of the ctenophoreMnemiopsis leidyiA. Agassiz, 1865 reveals a unique immune gene repertoire

Abstract

AbstractCtenophora are basal marine metazoans, the sister group of all other animals.Mnemiopsis leidyiis one of the most successful invasive species worldwide with intense ecological and evolutionary research interest. Here, we generated a chromosome-level genome assembly ofM. leidyiwith a focus on its immune gene repertoire. The genome was 247.97 Mb, with N50 16.84 Mb, and 84.7% completeness. Its karyotype was 13 chromosomes. In this genome and that of two other ctenophores,Bolinopsis micropteraandHormiphora californensis, we detected a high number of protein domains related to potential immune receptors. Among those, proteins containing Toll/interleukin-1(TIR2) domain, NACHT domain, Scavenger Receptor Cystein-Rich (SRCR) domain, or C-type Lectin domain (CTLD) were abundant and presented unique domain architectures inM. leidyi. M. leidyiseems to lackbona fideToll like Receptors, but it does possess a repertoire of 15 TIR2-domain containing genes. Besides, we detected abona fideNOD-like receptor and 38 NACHT-domain containing genes. In order to verify the function of those domain containing genes, we exposedM. leidyito the pathogenVibrio coralliilyticus. Among the differentially expressed genes, we identified potential immune receptors, including four TIR2-domain containing genes, all of which were upregulated in response to pathogen exposure. To conclude, many common immune receptor domains, highly conserved across metazoans, are already present in Ctenophora. These domains have large expansions and unique architectures inM. leidyi, findings consistent with the basal evolutionary position of this group, but still might have conserved functions in immunity and host-microbe interaction.