The Highly Repetitive Genome of Myxobolus rasmusseni, an Emerging Myxozoan Parasite of Fathead Minnows

Abstract

Myxozoans are a monophyletic taxon of approximately 2,400 described species of parasites from the phylum Cnidaria. The recent focus on their negative impacts on fisheries, on their evolution from free-living ancestors, and on their emergence into new fish host populations has stressed the critical need for genomic resources for this parasitic group. Here, we describe the genome assembly and annotation of Myxobolus rasmusseni, an emerging parasite of fathead minnows in Alberta, Canada. The assembly is 174.6 Mb in size, 68% of which is made up of repetitive elements, making it one of the most repetitive animal genomes sequenced to date. Through comparisons to other myxozoans, we show that widespread gene loss, a known phenomenon of this group of parasites, is consistent with closely related species. Additionally, we assembled the M. rasmusseni mitochondrial genome, which is nearly twice the size of the typical animal mitochondrial genome yet contains only five of the canonical mitochondrial protein-coding genes and open reading frames not found in other myxozoans. These results add to our understanding of the gene- and genome-level diversity observed in myxozoans.

Keywords: Myxozoa; gene loss; genome; parasite.

Fig. 1.

a) The change in status of BUSCO genes (eukaryote odb10) in the M. rasmusseni and M. honghuensis genome assemblies. The purple lines denote genes that are better represented in M. rasmusseni, and the orange lines denote the genes that are better represented in M. honghuensis. b) The mitochondrial genome of M. rasmusseni. Protein-coding genes are annotated in green and ribosomal RNA genes in red. Unannotated ORFs in purple, with asterisk denoting ORFs that have putative orthologs to those in other myxozoans.