De novogenome assembly and comparative genomics for the colonial ascidianBotrylloides violaceus

Abstract

Ascidians are invertebrate chordates with different modes of reproduction and solitary vs. colonial organization, as well as diverse genomes, morphological features, and regenerative capacities. The botryllid clade of ascidians are a growing model for coloniality, whole body regeneration, immune function, genome expansion, and the evolution of these traits. This study implements a hybrid assembly technique with cost-effective sequencing to produce a genome assembly and annotation for the botryllid ascidian, Botrylloides violaceus. A hybrid genome assembly was produced using Illumina, Inc. short and Oxford Nanopore Technologies long read sequencing technologies. The resulting assembly is comprised of 831 contigs, has a total length of 121 Mbp, N50 of 1 Mbp and a BUSCO score of 96.1\%. Genome annotation identified ~13,000 protein coding genes. Comparative genomic analysis with other tunicates reveals patterns of conservation and divergence within orthologous gene families even among closely related species. Characterization of the Wnt gene family, encoding signaling ligands involved in development and regeneration, reveals conserved patterns of subfamily presence and gene copy number among botryllids. We assembled and annotated the first genome for the colonial ascidian Botrylloides violaceus. This genome supports the use of economical genomic data from non-model organisms in the investigation of biological phenomena.