The Analysis Of Stuctural Characterister In Lepidopteran Mitochondrial Genomes

Lepidoptera is widely distributed around the world,including the well-known butterflies that can be used to monitor environmental changes and many important agricultural and forestry pests,which are one of the hotspots in mitochondrial genome research.The mitochondrial genome(mtgenome)is widely used in the evolution and phylogeny of Lepidoptera due to its stable genetic composition,relatively conservative gene arrangement,generally maternal inheritance,and rarely recombination.Therefore,this study supplemented the mtgenomic sequences of representative family-level elements in Lepidoptera through high-throughput sequencing(Paired-End 150 sequencing),especially the primitive taxon.A total of 110 lepidopteran mtgenomic sequences were newly sequenced and obtained.Combining the 1006 reported mtgenomic sequences in lepidoptera on NCBI,a total of 1116 mtgenomic sequences of lepidopteran insects were obtained as the research object.The corresponding mtgenomic characteristic of different superfamily and family levels were analyzed and summarized.The main results are as follows:1.The mtgenomes of Lepidoptere are circular closed double-stranded DNA molecules,containing 37 genes and a control region.The sequence length ranged from 13264 bp(Platyptilia sp.)-16535 bp(Ectropis obliqua Prout,1915),and the AT content ranged from76.0% to 86.6%,the highest of that appeared in Vietomartyria maoershana Liao,Hirowatari& Huang,2020.Moreover,the AT content of the other two micropterigoid sequences also reached to 85.5%,which is significantly higher than other superfamilies.According to the analysis of AT skew and GC skew,it is found that the base skew between AT and GC of the mtgenome at the superfamily Micropterioidea is more inclined to use T and G,while base skew between GC of the mtgenomes at other superfamilies in Lepidoptera is more inclined to use C.2.Among the 13 protein-coding genes,the use types of start codon only maintained strong consistency in atp6 and nad5(ATG and ATT,respectively).There are four types of stop codons,TAA,TAG,TA and T.There is a 7 bp overlapping region between atp8 and atp6 gene.Except for the superfamily Micropterigoidea,which is the overlapping sequence of ATGATAG,the other Lepidoptera are all ATGATAA.RSCU analysis shows that UUA(L)has the highest frequency of use among the 13 PCGs.In all 13 PCGs,the TA ratio at the second codon was significantly higher than the first and third codon,nearly displayed as "PCG-2>PCG-3>PCG-1".At the superfamily levels,"PCG-3> PCG-2> PCG-1" appears in the nad5 gene at the superfamily Micropterigoidea and the atp8 gene at the superfamily Calliduloidea,Carposinoidea,Choreutoidea and Mimallonoidea.3.Among the 22 tRNA genes,the average length ranged from 63 bp(trn S1)to 71 bp(trn K).The average length of 16 S r RNA and 12 S r RNA reached 1353 bp and 774 bp,respectively.Except for the trn S1 gene,the secondary structures of the remaining 21 tRNAs are typical clover structures.Except for the trn I,trn K and trn R gene,there is only one anticodon type in the remaining 19 tRNA genes.The rearrangement of tRNA genes in the Lepidoptera mtgenome at the superfamily level is mainly concentrated in the "trn M-trn I-trn Q" and "trn T-trn P" gene regions.4.The control region of the lepidopteran mitochondrial genomes is located between 12 S r RNA and trn M,with an average length of 439 bp and an average AT content of 93.5%.There are three conserved structures in the control region: the motif ATAGA,poly-T structure and poly-A structure.In the mtgenomes of some primitive moths,those three structures all have mutations in individual positions.However,the control region only exist the poly-T structure in the superfamily Hepialoidea.And the poly-T structure is located at the start region of the control region,followed by the 5’end of 12 S r RNA.The phylogenetic analysis result based on the complete mtgenome showed that the evolutionary relationship of the superfamily level in Lepidoptera is(Micropterioidea +(Neopseustoidea +(Hepialoidea +(Nepticuloidea +(Adeloidea +(Tischerioidea +Ditrysia))))),combined with the characteristics of the mtgenome of Lepidoptera,the 7 bp overlap between atp8 and atp6 genes is caused by the ATGATAG of the superfamily Micropterioidea evolved into ATAATAA of other lepidopteran taxons,and its mitochondrial gene rearrangement change of "trn Q-trn I-trn M" → "trn I-trn Q-trn M" → "trn I-trn Q-trn M" → "trn M-trn I-trn Q" and "trn P-trn T" → "trn T-trn P" is consistent with its evolution relationship.The results of this study will have certain scientific value and practical significance for elucidating the evolution characteristics of various taxons in Lepidoptera.