Studies On Complete Mitochondrial Genome Of Epinephelus Coioides And Epinephelus Akaara

By designing 13 pairs of primers used in PCR and sequencing, we obtain the complete mitochondrial genome sequences of Epinephelus coioides and Epinephelus akaara.The sequences were analyzed to discuss the mtDNA evolutionary characteristics of Epinephelini, and the phylogenetic relationship of some Perciforms species. The results are shown as follows:1. The mitogenome length of E.coioides and E.akaara is 16418bp and 16795bp, respectively. Both genome contents consist of the 13 protein-coding genes, 2 rRNAs, 22 tRNAs, and 1 control region. The nucleotide composition shows a nucleotide bias against G and especially in the twelve protein-coding genes encoded by the H-strand. The homologous protein-coding genes of the two groupers share the same initiation codons. Initiation codes of COI and ATP6 are GTG and CTG, respectively; and other 11 protein-coding genes are all ATG. The usage of termination codons includes TAA,TAG and T. Among the 22 tRNAs, except tRNA-Ser(GCT), the other 21 tRNAs have clover second structure with conservative anticodon loop and TΨC loop but variable DHU loop. In the control region, extended termination associated sequences (ETAS), central conserved domain (CD), and conserved sequence blocks (CSB) are identified. The control region is an AT rich region and also the most variable region in mtDNA. The length difference of control region sequence between the two groupers is obvious, which is mainly due to the difference of the length of sequence repeated units and the times of ETAS repeats.2. The compare of mitogenome sequences of the 3 known Epinephelini species (E.coioides, E.akaara and Plectropomus leopardus) shows the relative evolution rates of mtDNA regions: rRNA,tRNA < protein coding genes < L-strand origination region < control region. 13 protein-coding genes can be divided into 4 types according to their evolution rates: COI, COII, COIII < Cyt b, ND1, ND4, ND4L < ATP6, ND2, ND3, ND5 < ATP8, ND6. Among 22 tRNAs, tRNA-Gln, tRNA-Ser (TGA) and tRNA-Asn show the lowest evolution rates, while tRNA-Ser (GCT) and tRNA-Val show the fast.The complete mitogenome sequences of these 3 species were used to estimate their divergence time. The result of such analysis shows that the divergence time of E.coioides and E.akaara dates back to 15.4 MY, and the divergence time of P. leopardus and these two Epinephelus species are about 27.2 and 27.3 MY.3. With Sardinops melanostictus as the designated outgroup, phylogenetic tree, which invoke additional mitogenome sequences of other Perciformes fishes from GenBank, was constructed based on the maximum-parsimony (MP) methods. Several conclusions were drawn from the DNA sequences analysis: (1) suborders Labroidei, Gobioidei, Blennioidei and Gobiesocoidei are primitive groups in the analyzed Perciformes species, while suborders Zoarcoidei, Trachinoidei, Percoidei, Caproidei and Scombroidei are more recently diverged species; (2) the 6 species of family Scombridae, 3 species of family Carangidae, 4 species of family Cichlidae, and 4 species of suborder Gobioidei show monophyly severally. (3) Epinephelini is located within the recently diverged clades of the analyzed Perciformes species, and the family Serranidae which includes Epinephelini has the closest relationship with family Latidae and Sparidae, secondly Lutjanidae and Emmelichthyidae, thirdly Percidae and Centrarchidae.