Abstract
In this study, the complete mitochondrial genome of a hybrid, which was produced by sexual hybridization of Leiocassis longirostris (♀) and Pelteobagrus fulvidraco (♂), was obtained. The complete mitochondrial genome is 16 534 bp in length, including the typical structure of 22 transfer RNA genes, 13 protein-coding genes, 2 ribosomal RNA genes and the non-coding control region. Twenty-one site differences were found in overall length compared with the known mitochondrial sequence of L. Longirostris. About 2 site differences were located in rRNAs, 1 in tRNA, 4 in the control region and 14 in protein-coding genes. Furthermore, 14 variable bases of the protein-coding regions resulted in five variable amino acids, which were located in the ND1, ND2, COX3, ND4 and ND5, respectively.
Keywords: Hybrid, Leiocassis longirostris, mitochondrial genome, Pelteobagrus fulvidraco
Leiocassis longirostris and Pelteobagrus fulvidraco, which belong to the family Bagridae (Siluriformes), are two most important economic freshwater fishes (Wang et al. 2011; Liang et al. 2012). However, due to overfishing, environmental pollution and other human impacts, the wild populations have rapidly decreased. In order to synthesize their good traits, the hybrid was produced by female L. longirostris and male P. fulvidraco. Moreover, we sequenced the complete mitochondrial genome of the hybrid (GeneBank accession number KU133294) and compared with L. Longirostris and constructed a neighbour-joining phylogenetic tree based on COI sequences.
The hybrid individuals were collected from the Experiment Farm of YFI (Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Jingzhou City, Hubei Province, China). Seventeen primer pairs were used to amplify the complete mitochondrial genome. PCR products were purified and directly sequenced in an ABI 3730 capillary sequencer (Applied Biosystems, Forster, CA). DNA sequences were analyzed using the software Lasergene version 7.0 (DNASTAR Inc, Medison, WI). The phylogenetic tree was constructed using Mega5 (Arizona State University, AZ).
The complete mitochondrial genome of the hybrid of female L. longirostris and male P. fulvidraco was 16 534 bp in length, which consisted of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and a control region. Like other vertebrates, most mitochondrial genes were encoded on the H-strand except ND6 gene and eight tRNA genes. The overall base composition was 31.75% A, 26.84% T, 26.60% C and 14.81% G, with a high AT content of 58.59%. Compared with the mitochondrial sequence of L. Longirostris (NC_014586), 21 site differences were found between their mitochondrial genome. About 2 site differences were located in rRNAs, 1 in tRNA, 4 in control region and other 14 in protein-coding genes. Moreover, 14 variable bases in the protein-coding regions resulted in 5 variable amino acids, which were located in ND1, ND2, COX3, ND4 and ND5.
Thirteen protein-coding genes shared the start codon ATG except COX1, which was with GTG. Among them, 9 genes ended with complete stop codons TAA (COX1, ATPase 6, ATPase 8, ND5 and ND6) or TAG (ND1, ND2, ND3 and ND4L), the rest 4 genes ended with incomplete stop codons T–– (COX2, COX3, ND4 and Cyt b), which are presumably completed as TAA by post-transcriptional polyadenylation (Anderson et al. 1981; Boore 1999).
12S rRNA and 16S rRNA were 955 bp and 1679 bp in length, respectively. Twenty-two tRNA genes were interspersed between the rRNA and protein-coding genes. The major non-coding sequence was the control region (D-loop) with 892 bp. Comparison of the control region sequences revealed a total of four nucleotide divergences between the two varieties. The second non-coding sequence was the origin of light-strand replication (OL), similar to other fishes (Kim et al. 2004; Kartavtsev et al. 2007; Liang et al. 2012).
The results based on the phylogenetic tree showed that the hybrid of L. longirostris (♀) and P. fulvidraco (♂) were genetically closer than the other two species (Figure 1).
Figure 1.
Neighbour-joining phylogenetic tree based on COI sequences of the hybrid of Leiocassis longirostris (♀) and Pelteobagrus fulvidraco (♂), Pelteobagrus fulvidraco and Leiocassis longirostris.
Disclosure statement
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
Funding information
This study was supported by Special Scientific Research Funds for Central Non-profit Institutes, Chinese Academy of Fishery Sciences in China (2014A11JC05), Special Funds for National Science and technology Basic Work (2013FY110700) and National Infrastructure of Fishery Germplasm Resources of China.
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