Novel gene rearrangement pattern in Cynoglossus melampetalus mitochondrial genome: New gene order in genus Cynoglossus (Pleuronectiformes: Cynoglossidae).

Mitochondrial genome (mitogenome) structure and gene order are generally considered conserved in vertebrates. However, the flatfish (Pleuronectiformes) mitogenomes exhibit the most diversified gene rearrangement patterns. Here, we report a newly sequenced mitogenome of Cynoglossus melampetalus (Pleuronectiformes: Cynoglossidae). The total length of the C. melampetalus mitogenome is 16,651 bp, containing 13 protein-coding genes, two ribosomal RNAs, 22 transfer RNAs, a putative control region, and an L-strand replication origin. Like all previously reported tongue sole (Cynoglossinae) mitogenomes, the C. melampetalus tRNA-Gln gene is inverted from the light to the heavy strand (Q inversion), accompanied by the translocation of CR, which is downstream to the 3'-end of ND1. In addition, we observed a unique tRNA-Ile-Met-Glu (IMQ) gene order that differed from the tRNA-Glu-Ile-Met (QIM) order previously reported for other 14 Cynoglossinae mitogenomes. To our knowledge, it is the first report of two different patterns of mitogenomic gene-arrangement within the same genus in teleost. According to the Q inversion, Met pseudogene (ψMet) and long intergenic gap (186 bp) between M and Q genes, the observed gene rearrangement pattern were presumably supported by mitochondrial recombination and tandem duplication/random loss models. The reduced trend of the intergenic gap between Q and I also suggests that the event of gene rearrangement can be traced back to early Cynoglossinae differentiation.