The Complete Mitochondrial Genomes Of The Carettochelys Insculpta And Palea Steindachneri, And Their Phylogenetic Position Within Testudines

Turtle is a kind of ancient and highly specialized reptile. There are about 450 turtle species in existence in the whole world. Now with the increasing population, human activities affecting the rapid development and huge, turtles resources dwindling, some species are endangered, and even some species have not yet identified by scientists, it has been extinct. So studies on turtle are of great theoretical and practicfoodal importance.Mitochondrial (mt) DNA in vertebrates forms a double-stranded circular molecular of about 15-23 kb in size. Recently, mt genome has been widely employed as a useful marker for phylogenetic analyses of vertebrate, due to its maternal inheritance and relative lack of recombination, and the usefulness of mt genome has received much attention in turtle science. As of May 2010, complete mitochondrial genomes have been released from GenBank for 34 turtle species, but it was far from sufficient for studying reliable phylogeny of turtles.In our study, the complete nucleotide sequences of the mitochondrial genome (mtDNA) molecules from the Pig-nosed Turtle Carettochelys insculpta and wattle-necked softshell turtle Palea steindachneri were determined using PCR and sequencing technology. The size of molecules was 16 439 bp, and 17 243 bp, respectively. The genome organization, gene order, and base composition conformed to that of the typical vertebrate, including 22 tRNAs, 2 rRNAs, 13 protein-coding genes, as well as a control region. As most turtle mtDNA reported an extra nucleotide was discovered in NADH3 gene of Palea steindachneri, but contrasts with its apparent disappearance from Carettochelys insculpta. The control region of two tortoises is 972 bp and 1 736 bp in length respectively. In the Carettochelys insculpta the termination associated sequences (TAS),conserved sequence blocks F and 1-3(CSB F,1-3) were found. Several kinds of repeats (R1 (CA)9 and (AT)16) were discovered in the right domain of the region of Carettochelys insculpta. The 5'end of CR was identified tandem repeats (VNTR) of (5'-ATTTTACTTTTTTTTCTCTCCCGCGCCCAAGAGATATAAAACCCCTG TAT-3')5 in Palea steindachneri and one kind of repeat sequences, R1, (TATAT)4 in the 5'end of CR. The findings might be regarded as special molecular markers and applied to the molecular phylogenetics, the genetic relationship identification, as well as the conservation and study on species diversity of turtles.In this study, Neighbor joining (NJ), Maximum parsimony (MP), Maximum likelihood (ML) and Bayesian (BI) analyses were conducted based on 13 protein-coding genes from 17 taxa. NJ and MP analyses robustly supported that the earliest phylogenetic tree splits separating into three basal branches, the Pelomedusidae (Pelomedusa subrufa), the Carettochelyidae (C. insculpta) and an assemblage of 15 cryptodiran turtle species. In this result, the C. insculpta may be a representation of distinct suborder. while ML and BI analyses suggested that Carettochelyidae and Trionychidae formed a clade, which has the sister taxon to all other cryptodiran turtles. In the Trionychidae, Palea steindachneri and Pelodiscus sinensis firstly gather into one clade, and then form a group with Dogania subplana, Trionyx triunguis and Lissemys punctata.