Identification And Analysis Of Chemosensation,Detoxification,Immune Genes And Imidacloprid-responsive Genes In Bumblebee Genome

Bumblebees are one of important pollinators in both natural and agricultural ecosystems.Reports of many species in decline point to habits loss,pathogen transmission,pesticides usage and global climate change.To maintain the population size and diversity,mining and utilizing molecular resources of bumblebees become a hotter topic than conventional ecological measures.Decoded genus-wide bumblebee genomes provide a basis for further differential analysis in their environmental adaption and behavioral traits.Here,we annotated genes linked to bumblebees’ ecological traits and presume their function in response to insecticides.Firstly,we identified and classified chemosensory,detoxification and immune genes of 17 bee species in all 15 subgenus of genus Bomus.A total of 2,553 odorant receptor gene,303 gustatory receptor genes,372 ionotropic receptor genes,512 carboxyl/cholinesterase genes,717 cytochrome P450 monoxygenase genes,212 gluathione S-transferase genes and 3,179 immune genes were annotated.Some genes related to bumblebees olfactory and gustatory are evolved rapidly,for example,there was a net loss of more than 10 OR genes in subgenus Mendacibombus and Psithyrus.However,detoxification genes and immune genes have more stable gene counts among different bumblebee species.The total number of these genes was similar with honeybees and much smaller than in drosophillids and naophelines,which may due to their social lifestyle and mutualistic relationship with plants.Despite overall conservation of gene number,some single copy homologous genes showed evidence of positive diversifying selection in a subset of species.All this information is useful for comprehensive understanding of differences in bumblees biological traits and ecological adapation among all species.Secondly,we used RNA-seq to explore the expression changes of above genes after imidacloprid exposure,which is the most widely used neonicontinoid pesticides with the longest history.Bombus terrestris is domesticated and commercialized for pollination all around the world so we used it as the experimental subject.Differentially expressed genes in head,midgut,malpighian tube and fat body were captured after 0.5h,3h,6h and 10 d imidacloprid exposure,respectively.ATAC-seq was applied to predict transcriptional regulation regions of differentially expressed genes.The protein structure of CYP4 and CYP6,which may play an important role in response to imidacloprid,was modelled.Genus-wide homology analysis of these proteins is helpful to presume the gene function and infer their sensitivity to the insecticide.All differentially expressed genes captured in acute or chronic imidacloprid exposure experiments and the related transcriptional regulatory information laid the foundation not only for further understanding of molecular mechanism of pesticide damage to bumblebees,but also for developing and supervising new insecticides in the future.It may make followup utilizing insecticide-resistance genes and breeding insecticide-resistance bombus pollinators possible.