| Termites are known as lower-level semi-metamorphic,Isoptera insects,belonging to Arthropods,Insecta and Pterygota.The world's termites constitute over 2900 species in around 280 genera.The traditional classification is divided into 7 families and 14 subfamilies,in which Termitidae occupies more than 70%of the total number of termites.According to the recording of "Fauna Sinica",excepting for Mastotermit-idae and Serritermitidae,five families have been recorded in China.To date,China has recorded 4 families 44 genera 476 species.Isoptera is the only fully social insects excepting for Hymenoptera,which is primitive and ancient in the insects' classification system.Most of the termite species are important pests and harmful to houses,dams,warehouses,bridges and garden plants.And more importantly,they can quickly build groups,multiply and spread in different places,causing serious economic losses and destroies to new areas.In this study,we successfully sequenced mitochondrial genomes of Coptotermes amanii,Coptotermes sjostedti,Coptotermes intermedius,Coptotermes testaceus,Ancistrotermes sp.and Increitermes sp.by PCR amplification.And each sequence was carefully annotated and analyzed.At the same time,combining with other Isoptera termites' mitochondrial genomes in the database,which were published in NCBI,we have made systematic comparison and analysis about its base composition,amino acid composition,codon usage and so on.Some basic characteristics of the protein coding genes in the mitochondrial genome were sunmmarized.Finally,we have constructed the phylogenetic tree of 60 termites and made simple evolutionary relationship analysis.The main results of the study were listed below:1.The obtained sequence length of the above termites'mitochondrial genomes is 15754 bp,15765 bp,15766 bp,15752 bp,16595 bp and 16126 bp,respectively.And all of them share the same 37 typical genes and a non-coding region.The gene composition and order of the six mitochondrial genomes are consistent with the previously published termite species.2.In the base composition of the mitochondrial genome of the six termites,excepting for PCG-N and PCGs show T-skew,the remaining components show obvious A-skew,and the highest A+T content(74%)is in Increitermes sp..In addition,there are 16 to 20 gene intervals which length is changeable in the six termites(the longest gene interval between tRNAIle and tRNAGln,tRNASer(UCN)and ND1 or tRNAGln and tRNAMet)and 10 to 15 overlap regions(the largest overlap region between tRNATrp and tRNACys,ND1 and tRNALeu(CUN)or tRNAPhe and ND5).3.In the secondary structure of the 22 tRNAs,the 21 tRNAs form a typical clover leaf structure,excepting for tRNASer(AGN),which lacks a DHU arm and replaced by a simple loop.And there are a few base mismatches among secondary structures of tRNAs and G-U mismatch is the main type.In addition,among the all of the tRNA secondary structures,the anticodons are consistent with the previously published termite species.4.In this study,the A+T content of each component in the mitochondrial genomes of 36 termites is higher than 60%and show obvious AT bias.In addition,the A+T content of PCG-J is generally lower than that of PCG-N and the A+T content of D-loop is the highest.Ser and Leu are used frequently in all amino acids that make up the protein.In a variety of codons encoding the same amino acid,the average number of codons end with base U is often higher than the other codons,and the average number of UUU(F)is 179.1 times.5.Phylogenetic trees are constructed using PCGs datasets of 60 Isoptera termites.We can see from the results that the classification at the family level is consistent with the traditional classification.And the results of the two methods(ML and BI)are same basically,but the interspecies evolutionary position in the Coptotermes is different.Therefore,we have reconstructed the phylogenetic tree of the Coptotermes by expanding the rRNAs and tRNAs,and then basically determine the evolutionary positions of the four termites studied in this study. |
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