A chromosome-level genome assembly of the Echiura Urechis unicinctus

Abstract

Echiura is a distinctive family of unsegmented sausage-shaped marine worms whose phylogenetic relationship still needs strong evidence from the phylogenomic analysis. In this family, Urechis unicinctus is known for its high nutritional and medicinal value and adaptation to harsh intertidal conditions. Herein, we combined PacBio long-read, short-read Illumina and Hi-C sequencing, generating a high-quality chromosome-level genome assembly of U. unicinctus. The assembled genome spans ~1,138.6 Mb with a scaffold N50 of 68.3 Mb, of which 1,113.8 Mb (97.82%) were anchored into 17 pseudo-chromosomes. The BUSCO analysis demonstrated the completeness of the genome assembly and gene model prediction are 93.5% and 91.5%, respectively. A total of 482.1 Mb repetitive sequences, 21,524 protein-coding genes, 1,535 miRNAs, 3,431 tRNAs, 124 rRNAs, and 348 snRNAs were annotated. This study significantly improves the quality of U. unicinctus genome assembly, sets the footsteps for molecular breeding and further study in genome evolution, genetic and molecular biology of U. unicinctus.

Fig. 1

Overview of U. unicinctus genome. (a) Circos plot of genomic features. From outer to inner ring: (A) gene density; (B) GC content; (C) transposable element abundance; (D) Tandem repeat density. Insert: image of adult U. unicinctus. (b) Pseudochromosomes interaction heatmap of U. unicinctus based on Hi-C assembly. Color block indicates the intensity of interaction from yellow (low) to red (high).

Fig. 2

Venn diagram of functional annotation of the U. unicinctus protein-coding genes. The Venn diagram shows the shared and unique annotations among NR, KEGG, SwissProt, and InterPro.