The genome of the "Sea Vomit" Didemnum vexillum

Abstract

Background: Tunicates are the sister group of vertebrates and thus occupy a key position for investigations into vertebrate innovations as well as into the consequences of the vertebrate-specific genome duplications. Nevertheless, tunicate genomes have not been studied extensively in the past and comparative studies of tunicate genomes have remained scarce. The carpet sea squirt Didemnum vexillum is a colonial tunicate considered an invasive species with substantial ecological and economical risk.Results: We report a newly re-assembled genome of Didemnum vexillum. We used a hybrid approach that combines two genome sequencing technologies and also its first transcriptome. Started from 28.5 Gb Illumina and 12.35 Gb of PacBio data a new hybrid scaffolded assembly was obtained comprised of a total size of 517.55 Mb that increases contig length about 8-fold compared to previous, Illumina-only assembly. While still highly fragmented (L50=25284, N50=6539), the assembly is suffcient for comprehensive annotations of both protein-coding genes and non-coding RNAs.Conclusions: The draft assembly of the "sea vomit" genome provides a valuable resource for comparative tunicate genomics and for the study of the specific properties of colonial ascidians.Availability: Genome and annotation data as well as a link to a UCSC Genome Browser hub are available at http://tunicatadvexillum.bioinf.uni-leipzig.de/.