Genomic Study On Exorista Sorbillans,the Parasitic Fly On Silkworms

Exorista sorbillans is a dipteran parasitic fly that parasitizes on the domestic silkworm,Bombyx mori,and causes serious damage on sericulture.Due to the lack of whole genome information,the basic research on this species is much less than other types of pathogen diseases on silkworms.In this study,we used third generation sequencing technology to assemble a919 M high-quality genome for E.sorbillans.The genome assembly consists of 297 contigs with an N50 size of 12.3M.BUSCO estimation suggests the assembly is of99.8% completeness.Based on the chromosomal synteny to the closely related species,we further assembled these contigs into pseudochromosomes and identified the X chromosome.We have fully annotated E.sorbillans reference genome and found that it encodes as much as 70% repetitive contents,which is more than most reported insect genomes.By integrating transcriptome data and homologous alignments,we have generated a consensus gene set including 15,171 protein-coding genes,showing a 99.1% completeness.We have annotated the gene set with functional domains,Gene Ontology terms,and KEGG pathways,and found that 20%of predicted genes are specific to E.sorbillans.We conducted a comparative genomic study across 13 Oestridae species,using the model species Drosophila melanogaster as outgroup.We sorted out orthologs across these species and reconstructed a phylogenetic tree to clarify the evolution of Tachinidae.We estimated that the speciation of Tachinidae might occur 25 My.In comparison to other species,we found that E.sorbillans have experienced evident gene family expansion in the energy metabolism related pathways,as well as contraction in pathways related to xenobiotic chemical metabolism.In addition,E.sorbillans genome encodes a large number of functional domains related to cell membrane transport,recognition,and digestion system.We finally focused on three main gene families that are well concerned in insects.E.sorbillans encodes a full set of immune-related genes.The sets related to Toll,IMD,and JAK-STAT signaling pathways were found relatively conserved.Interestingly,melanization related genes were found over-represented in E.sorbillans,while genes encoding antimicrobial peptides and lysozymes were found less than other species.Detoxification-related gene families is relatively conserved,with an evident expansion in P450 genes.Regarding chemoreception related genes,olfactory receptor genes were duplicated in E.sorbillans,while genes encoding gustatory receptors and ionotropic receptors showed contracted.In addition,we have characterized genes showing differentially expressed between larval and adult stages,as well as femaleand male-biased genes.In summary,this study has generated a high-quality,fully annotated reference genome for E.sorbillans,providing an important resources for the basic studies on parasitic flies.