The complete mitochondrial genome of the hybrid of Takifugu fasciatus (♀) × T. flavidus (♂).

In the present study, the complete mitochondrial DNA sequence of the hybrid from Takifugu fasciatus (♀) × T. flavidus (♂) was sequenced and characterized. The genome sequence was 16 443 bp in size, and the gene order and contents were identical with those of congeneric species in the genus Takifugu. Comparing with the complete mitochondrial genome of its parents, the hybrid of T. fasciatus (♀) × T. flavidus (♂) was consistent with a maternal inheritance. All the initiation codons of protein-coding genes are ATG, except for COX1 that begins with GTG. The complete mitogenome of the hybrid of T. fasciatus (♀) × T. flavidus (♂) provides an important dataset for the exploration of mitochondrial inheritance mechanism.

Pufferfishes of the genus Takifugu are mainly distributed along the coastal regions of Asia (Cheng et al. 1975; Matsuura 1984). Among the pufferfishes cultured, Takifugu fasciatus and T. flavidus are the two most important species. But wild populations of two species have been decreased drastically because of overfishing and pollution. The hybrid of T. fasciatus (♀) × T. flavidus (♂) can be a commercially important edible fish due to its delicious taste and high nutritional value. However, there is no report for the complete genome of the hybrid of T. fasciatus (♀) × T. flavidus (♂).

In this study, the specimen of the hybrid of T. fasciatus (♀) × T. flavidus (♂) was obtained by artificial hybridization from the national breeding farm of pufferfish in Haian, China (N32°32′∼N32°43′; E120°12′∼E120°53′), stored in −80 °C refrigerator. On the basis of the mitogenome sequence of T. obscurus (GenBank accession number NC_011626), 12 pairs of primers were designed for polymerase chain reaction amplification and sequencing. The complete mitochondrial DNA sequence of the hybrid of T. fasciatus (♀) × T. flavidus (♂) was determined and it was deposited in GenBank database with accession number KT965279.

The mitogenome was 16 443 bp in length and contained 13 protein-coding genes, 22 tRNA genes, two rRNA genes and a major non-coding regions (D-loop region). All genes show the typical gene arrangement, which conforms to the vertebrate consensus (Chen et al. 2012; Prosdocimi et al. 2012). Except for eight tRNA (Gln, Ala, Asn, Cys, Tyr, Ser, Glu and Pro) genes and one protein-coding gene (ND6), most of these genes are encoded on the heavy strand (H-strand). The compositions of the hybrid mitochondrial genome include 30.02% A, 25.76% T, 29.09% C and 15.14% G, with a slight AT bias of 55.78% (Qiao et al. 2012). Most genes are either abutted or overlapped. The overlap of the ATPase genes appears to be common in most vertebrate mitochondrial genome (7–10 bp) (Broughton et al. 2001). The non-coding control region (D-loop) of the hybrid is 818 bp, flanked by tRNA and tRNA genes. All protein initiation codons are ATG, except for COX1 that begins with GTG. But, the termination codons of the 13 protein-coding genes were varied, among them, two genes (COXII and ND4) showed incomplete stop codons.

The maximum-likelihood tree (by MEGA5.05_Setup, Arizona State University, America) based on mitochondrial genome nucleotide sequences of the hybrid and the other 14 kinds of fish was constructed with 1000 bootstrap replicates (Figure 1). Three primary branches were supported, among them, T. chinensis, T. vernicularis, T. flavidus, T. xanthopterus, T. rubripes, T. obscurus, T. porphyreus, T. oblongus and T. exascurus clustered into one branch, and the hybrid of T. fasciatus (♀) × T. flavidus (♂) has a closer relationship with T. obscurus (female parent) than other species.

Figure 1.

Phylogenetic tree based on mitochondrial genome nucleotide sequences of the hybrid of Takifugu fasciatus (♀) × T. flavidus (♂) (KT965279) and the other 14 kinds of fish set using the ML method. Genetic distances are listed above the branches. GenBank accession numbers of the sequences were used for the tree as follows: Takifugu vernicularis (AP009532); T. flavidus (NC_024199); T. xanthopterus (AP009533); T. chinensis (AP009534); T. rubripes (AP006045); T. obscurus (NC_011626); T. porphyreus (NC_011628); T. oblongus (NC_011634); T. exascurus (NC_011622); Arothron hispidus (AP011930); A. mappa (AP011931); Mola mola (AP006238); Diodon holocanthus (AP009177); Thunnus thynnus (KF906720).