Sequence Analysis Of Mitochondrial DNA On Hyriopsis Schlegelii

In this research,25 pairs of primers were designed from conserved sequence of closely related bivalves to amplify the gonadal mitochondrion genomes in Hyriopsis schlegelii of F3 offsprings (one male and one female). After sequencing and splicing the fragments, the two kinds of gonad mtDNA were obtained. Results showed that the total length of male and female mitochondrial genome were 15961bp and 15939bp, nucleotide composition were A(37.1%),C(26'.7%),T(23.3%),G(12.9%) and A(37.1%),C(26.8%),T(23.2%),G(12.9%) respectively.All the 37 genes typically found in the metazoan mtDNA genome were identified in the schlegelii, which include 13 protein-coding genes,2 ribosomal RNA genes,22 transfer RNA genes, and 28 non-coding regions ranged from 1 bp to 393 bp in size. The genes, Protein-coding genes (ND1,ND2,ND6,Cytb),tRNA genes(tRNA-M, A, S, E, W, R, K, T, Y, L (CUA), N, P, F, Q, C, I, V, L (UAA), G, S) and rRNA genes(12SrRNA,16S rRNA), were encoded on the L strand. The genes, Protein-coding genes (ND3,ND4,ND5,ND4L,ATP6,ATP8,COX1,COX2,COX3) and tRNA genes(tRNA-D,tRNA-H), were encoded on the H strand.Comparison the protein-coding genes of the two sequences, the frequencies of transnational bases and transversional bases were 0.34%-7.34% and 0.00%-0.62%. There was a codon bias UUU (F) in the two mtDNA. Thirteen protein genes contained 4 initiation codons, ie. I(AUU,AUC),V(GUG),M (AUG)and L (UUG), all of which had complete stop codons(UAA or UAG). There is a codon bias of UUU(F) and an amino acids bias of Leu. All the tRNA in the two mtDNA can fold into configurations resembling the four-armed secondary structures. There were only 1-2bp different bases between male tRNA and female tRNA,which were found on acceptor stem,variable arm,TΨC stem and loop,D stem and loop.The 16S rRNA of male mtDNA was longer'than female. There were two TAAAAAAAAC tandem repeat on 573bp-592bp of male 16S rRNA, this region may be on the loop of its secondary structures. After analysising the non-coding regions, we found that there was an ORF between tRNA-E and tRNA-W of the two mtDNA. And the control region (CR), a noncoding region of DNA involved in replication of the mt genome, has not been identified in the male and female H. schlegelii.After comparing the nucleotide and amino acids divergence on COX1 between male and female gonadal mtDNA, and constructing a molecular phylogenetic tree based on COXI genes by MP method, we found that the two mtDNA didn't relate to Doubly-Uniparental Inheritance (DUI).Expect of the COX2-12SrRNA region, the mitochondrion gene order of H. schlegelii is same with Lampsilis ornate. The two MP-trees based on cytb gene sequences and mtDNA genomes showed the evolutionary position of H. schlegelii relative to that of 14 other bivalvia species. The result showed that H. schlegelii and H. cumingii had the closest relationship than others.