Characterization Of Complete Ribosome Sequence Of Four Species In Family Ixodidae

Tick is a kind of blood sucking ectoparasite,which often lives on the body surface of livestock and people.As a vector insect,it is the second largest vector after mosquito.It can carry pathogens between hosts,most of which are important zoonoses.Ticks are mainly divided into Ixodidae,Argasidae and Nuttalliellidae,among which the most common and most harmful to people and livestock is Ixodidae.Ribosome widely exists in cells,with high copy number of nucleic acid.Ribosome is the main marker gene of molecular classification method.Therefore,this study amplified and analyzed the ribosomal genomic sequences of four species of ticks,Dermacentor silvarum,Haemaphysalis japonica,Ixodes persalcatus and Haemaphysalis longicornis,which are seriously harmful to human and livestock in Northeast China,and provided reliable basis for molecular classification of four species of ticks.Firstly,all kinds of ticks were collected in the northeast of China,and each tick was identified by morphology and molecular biology.Then,5 Dermacentor silvarum,5 Haemaphysalis japonica and 5 Ixodes persalcatus in Heilongjiang Province,5 Haemaphysalis longicornis from Jilin Province and 5 Haemaphysalis longicornis from Liaoning Province,and 25 ticks in total were amplified by ribosome sequence.The sequences were further assembled and compared Length,composition and structural characteristics;finally,homology and evolution analysis.The results showed that the total length of ribosomes of four ticks was 8 629-11 346 bp,the length of ribosomes 18 S,5.8S and 28 S genes of four ticks were basically the same,the length of ribosomes ITS1 and ITS2 genes of different ticks changed greatly,and the length of ribosomes ITS1 and ITS2 genes of the same tick changed slightly.The IGS length of the same tick changed greatly.The intraspecific differences of ITS1 and ITS2 of Haemaphysalis longicornis in the same site were small,while the intraspecific differences of ITS1 and ITS2 of Haemaphysalis longicornis in different sites were relatively large.In this experiment,the IGS sequence of 25 ticks was 89 bp on the side near the 28 S boundary and 19 bp on the side near the 18 S boundary,and the similarity was 100%.This phenomenon was considered as the flank of the intergenic spacer.There are 5 pairs of specific repeat sequences in forest ticks,40 pairs of specific repeat sequences in chlorpyrifos,and one pair of repeat sequences is common to all three species except chlorpyrifos.The results showed that for the first time,25 ribosomal genome sequences of four species of ticks were obtained,with a length of 8629-11346 BP.The length of 18 S,28s and 5.8S of different species of ticks were similar or the same,but the length of ITS1 and ITS2 could show the specificity of species;the length of IGS had no characteristic rule between or within species,and the length of IGS was the main reason for the different length of ribosome.In addition,89 BP of IGS sequence near the 28 s boundary and 19 BP of IGS sequence near the 18 S boundary in 25 ticks were 100% similar,which was considered to be the flank of intergenic spacer.There are 5 pairs of specific repeat sequences in forest ticks,40 pairs of specific repeat sequences in chlorpyrifos,and one pair of repeat sequences is common to all three species except chlorpyrifos.By comparison,the homology of 18 S,ITS1,5.8S,ITS2,28 S and IGS among the four ticks of Ixodesidae were 95.2-99.8%,23.4-100%,96.1-100%,27.5-100%,88.0-100 % And 12.9 ~ 100%.At the same time,we can get the conservative sequence of six ribosomal sequences: 5.8S > 18 S > 28 s > ITS2 > ITS1 > IGS.Each evolutionary tree constructed with different marker genes is not completely consistent with the traditional taxonomy.The evolutionary tree constructed based on 18 S,ITS1,ITS2 and 28 s is consistent with the traditional taxonomy.Ribosomes 18 S,ITS1,ITS2 and 28 s are of great significance in molecular classification,but they can not effectively distinguish regional plants.5.8S can not be used as the basis of tick molecular classification because of its high conservation.IGS variation rate is too large and lack of variation law,which can not be used for tick evolution analysis,but its repeat sequence has certain rules.This study obtained for the first time the complete ribosomal genome sequence of 25 ticks of four species in family Ixodidae,and its structural characteristics and homology were analyzed,which enriched the data of ribosomal genome of chlorpyrifos family,determined the conservative sequence of each gene segment,constructed the phylogenetic tree of ticks with different ribosomal genes,and discussed the evolutionary relationship of ticks.