Study On Chemosensitivity-related Genes Of Citrus Fruit Fly Bactrocera(Tetradacus) Minax Based On Whole Genome Sequence

Citrus fruit fly Bactrocera(Tetradacus)minax(Enderlein)(Diptera: Tephritidae)is one of the most important fruit fly pests which can cause damage to the citrus and pomelo,and one of the most important pests concerned in the international fruit trade.Citrus fruit fly distributes in the area of 230-1850 m altitude of 24-33。N.It has already infested in more than 100 counties in Hunan,Hubei,Yunnan,Sichuan,Guizhou and Guangxi,and has caused damage to many fruits in Citrus,Rutaceae,and great economic losses were presented.Distribution and occurrence of the citrus fruit fly are closely related to citrus plants.During the long-term co-evolution,the fruit fly has formed a specific chemical information relationship with citrus plants,and has a specific perception-tendency-selection behavior and process for the specific chemicals of the Citrus genus.In that process,odor-related genes such as Odorant binding protein(OBPs),chemosensory protein(CSPs),odor receptors(ORs)genes and so on should play a key regulatory role.In order to clarify the genes involved in the regulation of chemical information of the pest and their regulatory roles,genome and transcriptome sequencing and other bioinformatics methods were used in this thesis.The genome characteristics and the genes number of citrus fruit fly were identified,and 6 transcripts for three stages were obtained.Based on eight homologous protein gene families,the evolutionary relationship between citrus fruit fly and other 20 insect species was identified.OBP,CSP and OR genes of the fruit fly were identified,and the specific OR genes of the family Tephritidae were found,and the specific expression pattern of those genes in three stages was clarified.The results are as follows.1.The whole genome of citrus fruit fly was sequenced for the first time by combining the second and third generation genome sequencing techniques,and the whole genome sequence of citrus fruit fly was obtained.102 G data,covering genome 300 X,was given by second-generation sequencing,while 5G data,covering genome 15 X,by third-generation sequencing.The genome size of the fruit fly was estimated to be 331 Mb based on Kmer analysis.The actual genome size by genome assembly technology was 340 Mb,which was basically consistent with the results of Kmer analysis.Sequencing parameters of the whole genome were that Scaffold N50 with 1.636 Mb,Contig N50 with 23278 bp,and GC content with 34.5%.The number of predicted coding protein genes was 17200,15868 and 22189,respectively by De novo-AUGUSTUS,Glimmer HMM and Genscan.The number of predicted coding protein genes was 12533,12265 and 9497,respectively by Hi CESAP,MAKER and RNAseq.The genome and gene functions of the fruit fly were annotated with a total of 12533 functional genes.2.Based on the whole genome,eight homologous protein gene families were used to analyze the evolutionary relationship between citrus fruit fly and other 20 insect species.It was found that citrus fruit fly and the other Bactrocera fruit fly,such as Bactrocera dorsalis,had a distant genetic relationship,and should have a close genetic relationship with mediterranean fruit fly Ceratitis capitata.3.The transcriptomes of 6 samples of larvae,pupae and adults of citrus fruit fly were sequenced,and 32067 expressed genes were obtained,with an overall coverage of 99.58%.16018 functional genes of the transcriptome were annotated.4.Twenty-five OBP genes of citrus fruit fly were identified.Combining with the transcriptome,the expression levels of different OBP genes in different states were determined,and it was found that 99c1 was highly expressed or extreme highly expressed in all stages.Four single-copy CSP genes were identified.The highest expression of CSP-1 was found in pupae,and the highest expression of CSP-2,CSP-3 and CSP-4 in adults.Overall,the expression of CSP-2 was higher than those of CSP-3 and CSP-4.Fifty-three OR genes were identified.Fourteen OR genes such as OR7 a were amplified in Tephritidae,and OR85 e gene was only amplified in Bactrocera cucurbitae,while OR88 a gene only did in Bactrocera oleae.5.Nine specific OR genes in Tephritidae were identified,named OR1,OR2,OR3,OR4,OR5,OR6,OR7,OR8 and OR9,respectively.Apart from OR9 gene,all the other eight OR genes were amplified in Tephritidae.Among which,OR3 gene had species-specific amplification in Bactrocera dorsalis.The above results on the whole genome,transcriptome and olfaction-related genes of the citrus fruit fly are helpful to enrich the research on olfaction regulation mechanism of the insects.It also will become the foundation for the research on chemical information and behavior regulation between citrus fruit fly and its host plants,and provide the support for the research and development of new control strategies and technologies of that pest.