Genome Sequencing And Transcriptome Analysis Of Chemosensory Genes Of Two Meloids

Hycleus cichorii and Hycleus phaleratus are commonly known as blister beetles,that can produce the potent defensive blistering agent cantharidin.Cantharidin and its derivatives have been used to treat cancers for many years.These two kinds of meloids are very important medicinal resources in our country,but there is a lack of genome reference until now.And some relationships among this family were unresolved due to the limitation of available mitochondrial information.In terms of transcriptomics,the study of chemosensory genes in insects are research hotspots in recent years,but there is a lack of information of the two meloids in this area.At the same time,cantharidin synthesis has a sexual dimorphism in most blister beetles,but the transcriptome data in this area are very scarce.In this thesis,the genomes and mitochondrial genomes of the two meloids were identified and analyzed.And some important functional genes were studied using transcriptome data.The result is:1.This is the first time that two draft genomes of blister beetles H.cichorii and H.phaleratus are reported.Most of the coding regions were obtained and BUSCO assessment showed that our assembly obtained more than 98 % of the Endopterygota universal single-copy orthologs.Comparison analysis showed that the completeness of coding genes in our assembly was comparable to other beetle genomes such as Dendroctonus ponderosae and Agrilus planipennis.Gene annotation yielded 13,813 and 13,725 protein-coding genes in H.cichorii and H.phaleratus,of which ~89 % were functionally annotated.Assembly of the both blister beetle genomes provide a valuable resource for future biosynthesis of cantharidin and comparative genomic studies of blister beetles and other beetles.2.The complete mitochondrial genome of H.cichorii and H.phaleratus are 15,758 and 15,780 bp in length,respectively.Phylogenetic analysis was performed based on 13 protein-coding genes of nine meloid species,by using Bayesian Inference.The result further confirmed that H.phaleratus and H.cichorii were closely related to H.marcipoli and H.chodschenticus,and all Hycleus species were recovered as a monophyly to sister to M.aulica.3.I identified 8 odorant binding proteins(OBPs),6 chemosensory proteins(CSPs),3 sensory neuron membrane proteins(SNMPs),16 odorant receptors(ORs),8 gustatory receptors(GRs),and 19 ionotropic receptors(IRs)in H.phaleratus and 5 OBPs,6 CSPs,6 SNMPs,11 ORs,5 GRs and 20 IRs in H.cichorii.The expansion of a ‘divergent IR' in Hycleus genus is found in our analysis.Among three SNMP sub-families,both SNMP1 and SNMP2 exhibited a consistent expression pattern,SNMP1 high expression in males and SNMP2 high expression in females;whereas SNMP3 were observed obviously higher expressed in H.cichorii than H.phaleratus.Notably,the genes for OBP1,OBP4,CSP1,OR2,IR3,IR4 and SNMP3 were differentially expressed in antenna between these two beetles;The differential expression of genes might be involved into species isolation.Our data will provide a basis for future species protection and biological research focusing on the blister beetle Hycleus.4.I obtained 37,422 sequences with a mean length of 845 bp by RNA-seq of H.cichorii.To eliminate background noise,the differentially expressed transcripts between the female and male using two pairs of samples were analyzed,one from the field and another reared in the laboratory.And I also identified 698 significant differentially expressed transcripts.The pathway enrichment analysis demonstrated that the up-regulated transcripts in the female were significantly enriched in signal processing and genetic material metabolism pathways.In contrast,pathways for substance and energy metabolism were enriched using the up-regulated transcripts from the male adult.These differences may relate to distinct physiological activities between the female and male.Finally,I identified the 8 key enzymes for cantharidin biosynthesis,which belong to the mevalonate(MVA)pathway.These results may help improve our understanding of the molecular mechanism of cantharidin biosynthesis and sexual dimorphism in blister beetles.