Mitochondrial Genome Comparison, Lineage And Evolution Of Orthoptera

The complete and nearly complete mitochondrial genome(mitogenomes)of Traulia minuta,Tagasta indica,Phlaeoba infumata,Sinopodisma tsinlingensis,Euchorthippus unicolor,Pseudoeocyllina brevipennisoides,Phaneroptera nigroantennata,Orophyllus sp.,Sinopodisma wulingshanensis,Pedopodisma tsinlingensis and Patanga japonica were obtained based on sanger sequencing using conserved primers of Orthoptera and the Hiseq2500 platform.We assembled mitogenomes from the high throughput data using the mitobim program.The 11 mitogenomes were annotated using the Staden Package and Geneious softwares and were analyzed the nucleotide composition,start and stop codons,gene interspacers and overlappings and secondary tructures of tRNAs.We used the methods of comparative genomics,phylogenetic genomics and evolutionary genomics to analyze 153 mitogenome sequences,including 11 newly sequenced,29 unpublished and 113 sequences downloaded from GenBank.Several findings were got as below:1.We obtained 11 orthopteran mitogenome sequences.The AT content was generally over 70%.AT content of the third codons was generally higher than the content of the first and second codons.The nucleotide compositions of the whole mitogenome(J strand),13PCGs,22tRNAs,2rRNAs and A+T-rich region all showed AT-skew and CG-skew;The most often used codons of protein coding genes are UUA,UCU,UCA and AC A;The secondary structures of 22 tRNAs in 11 species were consist with structures previously reported.2.We compared mitogenomes of S.tsinlingen,S.tsinlingensis,S.wulingshanensis,S.houshana and P.tsinlingensis::? AT content of the four Sinopodisma and one Pedopodisma mitogenomes were highest in Orthoptera.? The most consevered tRNAs were trnA,trnLCUN,trnF and trnG in five species,with only one nucleotide' variations.? The secondary structures of stem-loops were existed in A+T-rich region,and there were different tandem repeat elements and copy numbers in A+T-rich region.We used 13PCGs + 2 rRNAs data sets to build the phylogeny of Caelifera,supporting Pedopodisma as a separate genus.To further clarify its phylogenetic relationship,we built the BI tree using seven mitochondrial sequences and two nuclear genes of 3 Pedopodisma and 6 Sinopodisma.The results also supported the Pedopodisma as a separate genus.3.The comparative mitogneomics analysis in Orthoptera was as following:? The mitogenome was about 15.8 kb in length.? The nucleotide compositions was As>Ts>Cs>Gs,AT-skew and CG-skew were found in almost all the mitogenomes of orthopterans except Mirhipipteryx andensis and Mecopoda niponensis.? The overlapping and intergenic regions:The overlapping regions between atp6 and atp8 were 7bp in length and the sequence is ATGATAA.The overlapping regions between nad4L and nad4 were 7bp in length and the sequence was TTAACAT.Cox1,atp8,nad1,nad2,nad4,nad5 and nad6 all have non-standard start codons.Cox2,cox3,nad3,nad4L and cytb had standard start codons;The complete termination codon was TAA or TAG and the incomplete stop codon was T or TA.The gene rearrangement events had not often occurred.Only 11 mitogenomes exsisted gene rearrangements in 153 orthoperan mitogenomes.The T-stretches or the secondary structures located to its corresponding position may be related to mitogenome replication origion.The length of A+T-rich is mainly caused by the size and repeat numbers of randem repeat elements.4.The phylogenetic relationship of Caelifera based on different datasets was as followes:(Tridactyloidea +(Tetrigoidea +(Eumastacoidea +(Pneumoroidea +(Trigonopterygoidea +(Pyrgomorphoidea + Acridoidea)))))),which did not support the monophylies of Acrididae,Gomphoceridae,Catantopidae,Arcypteridae and Oedipodidae.Ensiferan phylogenetic tree showed Schizodactyloidea were located in the basal and Tettigonioiidea were divergent most recently.All the trees supported the monophylies of Tettigonioidea,Hagloidea,Grylloidea,but not the monophyly of Stenopelmatoidea.The phylogenetic relationships in the Tettigonioidea were as follows:(((Mecopodinae + Phaneropterinae)+ Pseudophllinae)+(Tettigoniinae +Bradyporinae)+(Gryllotalpinae+Meconematinae))).5.We used the PAML software to calculate dN/dS in the energy related mitochondrial protein encoding genes,All the value of dN/dS in the 13 PCGs encoding genes were less than 1,indicating that all genes experienced purifying selection;The dN/dS of 13 PCGs dataset and nad6 had significant differences between full-winged species and wingless species.This result showed that the winged insects had experienced a rigorous natural selection pressure in order to ensure the normal flight.While the wingless insects did not need more energy supplication and the slight harmful mutations were accumulated.In addition,the average values of dN/dS in cox1,cox2 and nad4 were relatively samll,indicating that these three genes had experienced a relatively rigorous natural selection pressure.