Extensive mitochondrial genomic analyses reveal dynamic gene order rearrangements in the class Octocorallia (Cnidaria: Anthozoa)

Abstract

The class Octocorallia comprises two major clades corresponding to the orders Scleralcyonacea and Malacalcyonacea, including over 3500 species that occur in various marine habitats. Unlike other animals, octocorallians possess two unusual mitochondrial genomic characters: a mismatch repair gene (mt-mutS) common to both clades and gene order rearrangements involving inversions of protein-coding genes known only in the Scleralcyonacea. mt-mutS is considered a major driver of gene order arrangements; however, it is not clear why gene order rearrangements are restricted to the Scleralcyonacea. Here, we report 83 mitochondrial genomes of the Malacalcyonacea. Mitochondrial genome sizes range from 18 to 20 Kbp due to insertion of non-coding sequences rather than gene duplications, and genome size is strictly conserved within genera/families. We discovered four novel mitochondrial gene order rearrangement patterns in Malacalcyonacea. Evidently, mitochondrial gene order rearrangements are common to both orders in octocorals, and mt-mutS may facilitate recombination that causes these dynamic mitochondrial gene order rearrangements.