Large-Scale Screening Of Horizontal Gene Transfers In Insecta And Functional Study Of A Courtship Gene

Insects are the most abundant and diverse lineage in the animal kingdom and comprise over one million known species that account for over 50% of all described living animals on Earth.Horizontal gene transfer(HGT)refers to the exchange of genetic material between species with reproductive isolation and is considered a driving force shaping prokaryotic and eukaryotic genomes.In recent years,there have been many reports on HGT in insects.For example,carotenoid biosynthesis genes transferred from fungi to aphids contribute to aphid body coloration,genes that neutralize phenolic glucosides acquired by whiteflies from plants contribute to whitefly detoxification capabilities,andapara-sitoid killing factor gene transferred from a virus to lepidopterans contributes to lepidopteran defense.These HGT-acquired genes help insects adapt to new environment and stand out in the evolution.However,previous studies have shown the occurrence of HGT in insects,but their taxon sampling strategies focused on eithera few insects of interest or on a specific order of insects.We systematically carried out a comprehensive investigation of HGTs using large-scale insect genomics,along with bioinformatics and molecular biology methods.In addition,this study examined how HGTs shaped insect genomes and how they innovated biological functions in insects.1.Numerous horizontal gene transfers into insects.Using a robust and conservative phylogeny-based approach to examine the protein sequence of each of the nearly 3 million genes in the high-quality genomes of 218 insects,we systematically identified 1,410 HGT genes in 192 insect genomes that were likely acquired via 741 distinct events from non-metazoan source.These insect species include various butterflies,moths,beetles,planthoppers,and bees.On average,Lepidoptera(eg,diamondback moth and small white butterfly)acquired 16 HGT genes/species,Hemiptera(eg,brown planthopper)acquired 13 HGT genes/species,Coleoptera(eg,the red flour beetle)acquired 6 HGT genes/species,and Hymenoptera(eg,bees and parasitoid wasps)acquired 3 HGT genes/species.From the source of HGT’s donor,79% of HGT genes stem from bacteria,13.8% from fungi,2.6% from viruses,3% from plants,and 1.6% from unknown donors.2.Origin of introns in HGT-acquired genes and adaptation of HGT in insects.To determine the fate of transferred genes in insects,we characterized the gene structures of 1,410HGT-acquired genes in the putative donor and recipient genomes as well as of all native insect genes.We found that repeat-rich intron gains from native insect genomes,which enabled these foreign genes to increase their lengths toward the average length of native genes,were likely involved in adaptation of HGTs in insect genomes.Collectively,HGT-acquired genes containing introns exhibited substantially higher expression levels than genes lacking introns,suggesting that intron gains were likely involved in HGT adaptation,thereby avoiding being removed in the long-term evolution and surviving in insect genomes.3.The last common ancestor of moths and butterflies horizontally acquired a foreign gene that enhances male courtship behavior.We found that the prevalent HGT-acquired gene LOC105383139 was transferred into the last common ancestor of moths and butterflies from a donor in the bacterial genus Listeria.We used the CRISPR-Cas9 system to knock out the gene LOC105383139 in the diamondback moth Plutella xylostella,a serious agricultural pest of crucifer vegetables.We initially found that knockout(MT-139)moths have a much lower number of offspring but have no significant differences in five develop-mental phenotypes,including body size,feeding,movement,testis size,and sperm activity.Through further observations,we found that MT-139 moths had apparently lower mating rates than WT moths.In words,HGT-acquired gene LOC105383139 enhances male courtship behavior in moths and butterflies.In summary,this study elucidated the distribution,adaption and functional identification of male courtship-associated gene in 218 insects,and highlighted the importance of HGT in insect evolution and adaptation.It contributed to our understanding of HGTs in insect diversity and adaptation and its impact on agriculture.