Comparative And Phylogenetic Analysis Of The Mitochondrial Genomes In The Subfamily Chaitophorinae

The insect mitochondrial genomes are extensively used in evolutionary and phylogenetic studies because of outstanding characteristics such as the small genome size,relatively stable gene arrangement,accelerated evolutionary rate and general maternally inheritance.The development of analysis methods and sequencing technologies have leaded to widely study of phylogenetic based on mitochondrial genomes.Previous phylogenetic studies based on mitochondrial genomes mainly focused on the higher taxon of insect such as intraordinal,interordinal and interclass studies,while phylogenetic studies of subfamily or lower was few.A lot of studies found that the higher-level phylogeny relationgships based on mitochondrial genomes had some inevitable problems,such as long-branch attraction and nucleotide substitution saturation which can lead to the unreasonable results.Without these problems in subfamily or lower taxon,the mitochondrial genome is a powerful moceluar markers to study the phylogeny relationgships in these taxa.The subfamily Chaitophorinae,which include 12 genera belonging to Chaitophorini tribe and Siphini tribe,is an important group in Hemiptera,Aphididae.The species of Chaitophorinae are monophagous and holocyclic.The hosts of Chaitophorini and Siphini are deciduous trees and monocotyledonous plants respectively.Previous studies on the Chaitophorinae subfamily were mainly about species identification,description of morphological characteristics,host plants,observation of biological habits and geographical distribution.The phylogenic study of the Chaitophorinae subfamily was limited by molecular data on these groups,because of difficulty on sequencing of mitochondrial genomes of aphid.None of mitochondrial genome from the Chaitophorinae subfamily was reported to date.Bulk sequencing of mitochondrial genomes and reconstruction of phylogenetic relationship within Chaitophorinae subfamily are important to understand evolutionary history of the subfamily,discuss the association of the subfamily with host plant and promote the study of mitochondrial genome of aphid.In this study,the mitochondrial genomes of 22 species from the Chaitophorinae subfamily were sequenced,annotated and compared.The phylogenetic ralationships within this subfamily were reconstructed using the BI and ML methods based on mitochondrial sequences.The main conclusions were as follows.(1)Partial mitochondrial genomes were obtained from 22 species.The sequences length of genomes in 21 species ranged from 13459 bp(Periphyllus acericola)to 15384 bp(Periphyllus diacerivorus)accounting for about 87% to 99% of the complete genomes,while 10355 bp nucleotides were obtained in Trichaitophorus foliatus sp.nov.The tRNAArg-nad5 region were difficult to be sequenced because of high AT content and interference of pseudogenes.All species had the same arrangement as the ancestral insect without gene rearrangement event in the Chaitophorinae subfamily.All PCGs(protein coding genes)started with the regular codons ATN and stopped with the codons TAA\TAG\T.The longest overlap of genes(20 bp)located between atp6 and atp8,the longest intergenic ranged from 29 bp to 71 bp.(2)In 22 mitochondrial genomes,the A+T content ranged from 81.55% to 84.96% revealing strongly AT-biased(A+T% > G+C%).The obviously negative AT-skew and GC-skew revealed T and C richer than A and G respectively.The Phe,Leu and Ile were the first three frequent amino acids,and TTT(Phe),TTA(Leu)and ATT(Ile)were the first three frequent codons in Chaitophorinae.(3)The PCGs nonsynonymous substitutions(Ka),synonymous substitutions(Ks)and Ka/Ks were calculated to explore the evolution rates of PCGs for every species based on Pterocomma pilosum.The value of Ka,Ks and Ka/Ks were less than one which indicated purify selection in the PCGs.Thus,the PCGs can be used for phylogenetic analysis of the Chaitophorinae.The Siphini species showed lower evolutionary rate than Chaitophorini species,except Periphyllus acerihabitans.(4)The BI and ML analyses showed highly similar topologies with subtle differences on posterior probability and bootstrap.The monopoly of Chaitophorini and Siphini was supported by high support values.Sipha and Chaetosiphella were clustered together as a paraphyly group in the Siphini,while Laingia psammae located at the basal positon of the Siphini.Periphyllus acerihabitans and Periphyllus acericolathe located at the basal position of Chaitophorini formed a sister group with the rest species in Chaitophorini.The other Periphyllus species clustered with(Trichaitophorus +(Yamatochaitophorus))formed a sister group.Lambersaphis pruinosa nested within Chaitophorus,and generated paraphyly group in Chaitophorini.