Glycosyltransferases: the multifaceted enzymatic regulator in insects

Prevalence of insecticide resistance and enhanced detoxifying enzymes in field populations of Tuta absoluta (Lepidoptera: Gelechiidae) in the major Tomato growing regions of South India

South American pinworm Tuta absoluta (Meyrick) is an invasive and major tomato pest that attained resistance or reduced susceptibility to most insecticides used in their management due to repeated and intensive applications. This study aimed to find the levels of resistance in T. absoluta populations collected from South Indian states against novel insecticides such as chlorantraniliprole 18.5% SC, flubendiamide 39.35% SC, spinosad 45% SC, indoxacarb 14.5% SC, and emamectin benzoate 5% SG using leaf dip bioassay. Among the eight populations collected from major tomato growing belts spanning three states of South India (Andhra Pradesh, Karnataka and Tamil Nadu), Krishnagiri of Tamil Nadu showed the highest level of resistance to flubendiamide and the least resistance was shown by the Tirupati population, with a resistance ratio of 174.89 and 2.24, respectively. Significant correlation was found between LC50 values of flubendiamide and chlorantraniliprole (0.859), emamectin benzoate and flubendiamide (0.855) and spinosad and emamectin benzoate (0.866). The biochemical assay conducted to quantify the mixed function oxidase (MFO), carboxyl/choline esterase (CCE) and glutathione S-transferase (GST) in the T. absoluta larval populations showed an increased level of MFO, CCE and GST in Krishnagiri population with 15.59, 1.72 and 6.02-fold, respectively compared to susceptible population. It showed that the detoxification enzyme plays an important role in the insecticide resistance of the field population of T. absoluta. The results serve as an initial assessment for further understanding of the molecular mechanisms of insecticide resistance at the genetic level to design and implement successful insecticide resistance management strategies.

pH-responsive nanoparticles for oral delivery of RNAi for sustained protection against Spodoptera exigua

To enhance the RNAi efficiency of dsRNA against the Spodoptera exigua through a feeding method, we developed a pH-responsive nanoparticle, chitosan-polyethylene glycol-carboxyl (CS-PEG-COOH). This nanoparticle enhances RNAi efficiency by improving dsRNA stability in the midgut of S. exigua and can intelligently release dsRNA under alkaline conditions. Firstly, the CS-PEG-COOH carrier was prepared via cross-linking reactions, and the mass ratio of dsRNA to CS-PEG-COOH was obtained using electrophoretic mobility. The carrier composite materials were then characterized using isothermal titration calorimetry (ITC), transmission electron microscopy (TEM), atomic force microscopy (AFM), and Zeta potential analysis. The stability and delivery efficiency of the dsRNA/CS-PEG-COOH complex were then verified using electrophoretic mobility and fluorescence labeling methods. Finally, the RNAi efficiency and synergistic mechanism of the complex were analyzed using feeding methods and RNA-seq. The results show that CS-PEG-COOH (40.16 nm size, + 6.44 mV charge) forms a clustered complex with dsRNA through hydrogen bonding and hydrophobic interactions. CS-PEG-COOH significantly enhancing the stability and delivery efficiency of dsRNA in the midgut of S. exigua. Additionally, at pH > 8, dsRNA could be released from dsRNA/CS-PEG-COOH. The RNAi results showed that, dsRNA/CS-PEG-COOH could effectively inhibit the expression of the Acetylcholinesterase (Ace1 + Ace2) gene (65 %), and led to significantly increase mortality (51.82 %), a prolonged developmental period (25 %) and reduced egg production (22.02 %). The physiological and molecular synergistic mechanisms were revealed by RNA-seq analysis. The CS-PEG-COOH-loaded dsACE1 + dsACE2 led to down-regulation of genes related to drug metabolism, hormone synthesis, and stratum corneum biosynthesis, which inhibited insect growth and development. Overall, We developed an appropriate delivery method for dsRNA application in Lepidoptera, providing a basis for developing RNA pesticides with high efficiency and environmental safety.

Distinct assembly processes of intestinal and non-intestinal microbes of bark beetles from clues of metagenomic insights

Ips (Curculionidae: Scolytinae) bark beetles (BBs) are ecologically and economically devastating coniferous pests in the Northern Hemisphere. Although the microbial diversity associated with these beetles has been well studied, mechanisms of community assembly and the functional roles of key microbes remain poorly understood. This study investigates the microbial community structures and functions in both intestinal and non-intestinal environments of five Ips BBs using a metagenomic approach. The findings reveal similar microbial community compositions, though the α-diversity of dominant taxa differs between intestinal and non-intestinal environments due to the variability in bark beetle species, host trees, and habitats. Intestinal microbial communities are predominantly shaped homogenizing dispersal (HD) and undominated processes (UP), whereas non-intestinal microbial communities are primarily driven by heterogeneous selection (HS). Functional analysis shows that genes and enzymes associated with steroid biosynthesis and oxidative phosphorylation are primarily found in non-intestinal fungal symbionts Ogataea, Wickerhamomyce, Ophiostoma, and Ceratocystis of Ips species. Genes and enzymes involved in degrading terpenoids, phenolic compounds, and polysaccharides are predominately found in the intestinal Acinetobacter, Erwinia, and Serratia. This study provides valuable and in-depth insights into the symbiotic relationships between Ips BBs and their microbial partners, enhancing our understanding of insect-microbe coevolution and suggesting new strategies for pest management.

The UDP-glycosyltransferase UGT352A3 contributes to the detoxification of thiamethoxam and imidacloprid in resistant whitefly

Uridine diphosphate (UDP)-glycosyltransferases are essential phase-II detoxification enzymes that glycosylate lipophilic endogenous and xenobiotic compounds and they are thought to play a role in driving the evolution of insecticide resistance. To examine if the resistance to thiamethoxam and imidacloprid was associated with enhancement of UDP-glycosyltransferase in the whitefly, Bemisia tabaci, we first conducted UDP enzyme activity assays in resistant and sensitive strains in the absence and presence of UGT inhibitors. We found that the UGT enzyme content of resistant whitefly was significantly 5.02- to 10.69-fold higher than that of sensitive whitefly. Individual UGT inhibitors effectively inhibited UGT activity in resistant strains and their effect was synergistic when applied in combination. We then used bioinformatic, molecular, genetic and in silico approaches to determine if UGT352A3 encoded a key enzyme linked to neonicotinoid resistance. In resistant strains, UGT352A3 expression was elevated 1.8- to 6.6-fold compared to susceptible strains, which correlated with higher resistance ratios. RNAi-mediated knockdown of UGT352A3 in resistant whitefly strains significantly heightened their sensitivity to the insecticides, thiamethoxam and imidacloprid. Molecular docking analyses further confirmed a strong binding affinity between UGT352A3 and thiamethoxam and imidacloprid, which supported a role in their metabolism. These findings suggest that UGT352A3 is a critical factor in the development of resistance to thiamethoxam and imidacloprid in whitefly, underscoring its important potential as a new pest resistance management target.

A Head-Specific Transcriptomic Study Reveals Key Regulatory Pathways for Winter Diapause in the Mosquito Culex pipiens

The primary vector of the West Nile virus, Culex pipiens, undergoes reproductive dormancy during the adverse winter season. While our current understanding has mainly focused on cellular signals and phenotypic shifts occurring at a global scale during diapause, information on tissue-specific transcriptomic changes remains limited. This knowledge gap is a major challenge in interpreting the regulatory mechanisms at the tissue level. To address this, the present work utilized RNA-seq technology to investigate the transcriptional changes in the head that house the brain and crucial endocrinal organs such as corpora allata. We obtained RNA samples from the heads of diapausing and nondiapausing female mosquitoes at two specific time intervals, ZT0 and ZT16, and then subjected them to sequencing. Our results revealed differences in differentially expressed genes between diapause and non-diapause at ZT0 and ZT16, highlighting the phenotypic and diel variations in gene expression. We also selected twelve genes associated with the diapause phenotype and examined the transcript abundance at six different time points over 24 h. qRT-PCR analysis showed similar up- and downregulation of transcripts between the diapause and nondiapause phenotypes thus validating the results of RNA-seq. In summary, our study identified new genes with phenotypic and diel differentiation in their expression, potentially linking photoperiod to seasonal reproductive dormancy in insects. The newly presented information will significantly advance our understanding of head-specific genes crucial for insect diapause.

Transgenic overexpression of UDP glycosyltransferase gene UGT41A3 induces resistance to nucleopolyhedrovirus in Bombyx mori

Bombyx mori nuclear polyhedrosis, caused by B. mori nucleopolyhedrovirus (BmNPV), threatens sericulture seriously. To explore strategies for controlling it, the UDP glycosyltransferase gene UGT41A3 (BmUGT41A3) was targeted. UGT is involved in exogenous substances detoxification and endogenous biomass regulation in insects. Early embryos of the BmNPV-sensitive variety 'HYB' were used to obtain the transgenic line HYB-UGT41A3, overexpressing BmUGT41A3 under the IE1 promoter. qPCR results revealed that, compared with the wild-type control 'HYB', BmUGT41A3 was upregulated during the individual developmental stages of HYB-UGT41A3 from silkworm eggs to fifth-instar larvae; peak expression was observed in the third-instar larvae, which presented the most significantly upregulated expression. Individual-tissues qPCR results revealed that BmUGT41A3 expression was highest in the hemocytes of HYB-UGT41A3, followed by the midgut, whereas expression in HYB was very low. Gradient feeding of BmNPV on HYB-UGT41A3 and control 'HYB' larvae on the first day of the second-instar stage. The results revealed that the LC50 of HYB-UGT41A3 reached 4.040 × 107 particles/mL, which was 20-fold greater than that of HYB. The decrease in the BmNPV load was more significant in HYB-UGT41A3 than in HYB at 48 h after viral inoculation. These results indicate BmUGT41A3 overexpression inhibits BmNPV proliferation and improve resistance to BmNPV in B. mori.

Disarming the defenses: Insect detoxification of plant defense-related specialized metabolites

The ability of certain insects to feed on plants containing toxic specialized metabolites may be attributed to detoxification enzymes. Representatives of a few large families of detoxification enzymes are widespread in insect herbivores acting to functionalize toxins and conjugate them with polar substituents to decrease toxicity, increase water solubility and enhance excretion. Insects have also developed specific enzymes for coping with toxins that are activated upon plant damage. Another source of detoxification potential in insects lies in their microbiomes, which are being increasingly recognized for their role in processing plant toxins. The evolution of insect detoxification systems to resist toxic specialized metabolites in plants may in turn have selected for the great diversity of such metabolites found in nature.

Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are associated with insecticide resistance in the major malaria vectors Anopheles gambiae s.l. and Anopheles funestus

Malaria remains one of the highest causes of morbidity and mortality, with 249 million cases and over 608,000 deaths in 2022. Insecticides, which target the Anopheles mosquito vector, are the primary method to control malaria. The widespread nature of resistance to the most important insecticide class, the pyrethroids, threatens the control of this disease. To reverse the stall in malaria control there is urgent need for new vector control tools, which necessitates understanding the molecular basis of pyrethroid resistance. In this study we utilised multi-omics data to identify uridine-diphosphate (UDP)-glycosyltransferases (UGTs) potentially involved in resistance across multiple Anopheles species. Phylogenetic analysis identifies sequence similarities between Anopheline UGTs and those involved in agricultural pesticide resistance to pyrethroids, pyrroles and spinosyns. Expression of five UGTs was characterised in An. gambiae and An. coluzzii to determine constitutive over-expression, induction, and tissue specificity. Furthermore, a UGT inhibitor, sulfinpyrazone, restored susceptibility to pyrethroids and DDT in An. gambiae, An. coluzzii, An. arabiensis and An. funestus, the major African malaria vectors. Taken together, this study provides clear association of UGTs with pyrethroid resistance as well as highlighting the potential use of sulfinpyrazone as a novel synergist for vector control.

Duplications and Losses of the Detoxification Enzyme Glycosyltransferase 1 Are Related to Insect Adaptations to Plant Feeding

Insects have developed sophisticated detoxification systems to protect them from plant secondary metabolites while feeding on plants to obtain necessary nutrients. As an important enzyme in the system, glycosyltransferase 1 (GT1) conjugates toxic compounds to mitigate their harm to insects. However, the evolutionary link between GT1s and insect plant feeding remains elusive. In this study, we explored the evolution of GT1s across different insect orders and feeding niches using publicly available insect genomes. GT1 is widely present in insect species; however, its gene number differs among insect orders. Notably, plant-sap-feeding species have the highest GT1 gene numbers, whereas blood-feeding species display the lowest. GT1s appear to be associated with insect adaptations to different plant substrates in different orders, while the shift to non-plant feeding is related to several losses of GT1s. Most large gene numbers are likely the consequence of tandem duplications showing variations in collinearity among insect orders. These results reveal the potential relationships between the evolution of GT1s and insect adaptation to plant feeding, facilitating our understanding of the molecular mechanisms underlying insect-plant interactions.

Structural and functional studies reveal the molecular basis of substrate promiscuity of a glycosyltransferase originating from a major agricultural pest

The two-spotted spider mite, Tetranychus urticae, is a major cosmopolitan pest that feeds on more than 1100 plant species. Its genome contains an unprecedentedly large number of genes involved in detoxifying and transporting xenobiotics, including 80 genes that code for UDP glycosyltransferases (UGTs). These enzymes were acquired via horizontal gene transfer from bacteria after loss in the Chelicerata lineage. UGTs are well-known for their role in phase II metabolism; however, their contribution to host adaptation and acaricide resistance in arthropods, such as T. urticae, is not yet resolved. TuUGT202A2 (Tetur22g00270) has been linked to the ability of this pest to adapt to tomato plants. Moreover, it was shown that this enzyme can glycosylate a wide range of flavonoids. To understand this relationship at the molecular level, structural, functional, and computational studies were performed. Structural studies provided specific snapshots of the enzyme in different catalytically relevant stages. The crystal structure of TuUGT202A2 in complex with UDP-glucose was obtained and site-directed mutagenesis paired with molecular dynamic simulations revealed a novel lid-like mechanism involved in the binding of the activated sugar donor. Two additional TuUGT202A2 crystal complexes, UDP-(S)-naringenin and UDP-naringin, demonstrated that this enzyme has a highly plastic and open-ended acceptor-binding site. Overall, this work reveals the molecular basis of substrate promiscuity of TuUGT202A2 and provides novel insights into the structural mechanism of UGTs catalysis.

Toll receptor ligand Spätzle 4 responses to the highly pathogenic Enterococcus faecalis from Varroa mites in honeybees

Honeybees play a major role in crop pollination, which supports the agricultural economy and international food supply. The colony health of honeybees is threatened by the parasitic mite Varroa destructor, which inflicts physical injury on the hosts and serves as the vector for variable viruses. Recently, it shows that V. destructor may also transmit bacteria through the feeding wound, yet it remains unclear whether the invading bacteria can exhibit pathogenicity to the honeybees. Here, we incidentally isolate Enterococcus faecalis, one of the most abundant bacteria in Varroa mites, from dead bees during our routine generation of microbiota-free bees in the lab. In vivo tests show that E. faecalis is only pathogenic in Apis mellifera but not in Apis cerana. The expression of antimicrobial peptide genes is elevated following infection in A. cerana. The gene-based molecular evolution analysis identifies positive selection of genes encoding Späetzle 4 (Spz4) in A. cerana, a signaling protein in the Toll pathway. The amino acid sites under positive selection are related to structural changes in Spz4 protein, suggesting improvement of immunity in A. cerana. The knock-down of Spz4 in A. cerana significantly reduces the survival rates under E. faecalis challenge and the expression of antimicrobial peptide genes. Our results indicate that bacteria associated with Varroa mites are pathogenic to adult bees, and the positively selected gene Spz4 in A. cerana is crucial in response to this mite-related pathogen.

Genetic independence between traits separated by metamorphosis is widespread but varies with biological function

Why is metamorphosis so pervasive? Does it facilitate the independent (micro)evolution of quantitative traits in distinct life stages, similarly to how it enables some limbs and organs to develop at specific life stages? We tested this hypothesis by measuring the expression of 6400 genes in 41 Drosophila melanogaster inbred lines at larval and adult stages. Only 30% of the genes showed significant genetic correlations between larval and adult expression. By contrast, 46% of the traits showed some level of genetic independence between stages. Gene ontology terms enrichment revealed that across stages correlated traits were often involved in proteins synthesis, insecticide resistance and innate immunity, while a vast number of genes expression traits associated with energy metabolism were independent between life stages. We compared our results to a similar case: genetic constraints between males and females in gonochoric species (i.e. sexual antagonism). We expected selection for the separation between males and females to be higher than between juvenile and adult functions, as gonochorism is a more common strategy in the animal kingdom than metamorphosis. Surprisingly, we found that inter-stage constraints were lower than inter-sexual genetic constraints. Overall, our results show that metamorphosis enables a large part of the transcriptome to evolve independently at different life stages.

Genome and transcriptome of Ips nitidus provide insights into high-altitude hypoxia adaptation and symbiosis

Ips nitidus is a well-known conifer pest that has contributed significantly to spruce forest disturbance in the Qinghai-Tibet Plateau and seriously threatens the ecological balance of these areas. We report a chromosome-level genome of I. nitidus determined by PacBio and Hi-C technology. Phylogenetic inference showed that it diverged from the common ancestor of I. typographus ∼2.27 mya. Gene family expansion in I. nitidus was characterized by DNA damage repair and energy metabolism, which may facilitate adaptation to high-altitude hypoxia. Interestingly, differential gene expression analysis revealed upregulated genes associated with high-altitude hypoxia adaptation and downregulated genes associated with detoxification after feeding and tunneling in fungal symbiont Ophiostoma bicolor-colonized substrates. Our findings provide evidence of the potential adaptability of I. nitidus to conifer host, high-altitude hypoxia and insight into how fungal symbiont assist in this process. This study enhances our understanding of insect adaptation, symbiosis, and pest management.

Exploring Gut Microbiome Variations between Popillia japonica Populations of Azores

Popillia japonica (Coleoptera: Scarabaeidae), is an emerging invasive pest in Europe and America. In the Azores, this pest was first found on Terceira Island during the sixties and soon spread to other islands. The rate of infestation differs between islands, and we hypothesized that microbiome composition could play a role. Therefore, we sampled 3rd instar larvae and soil from sites with high and low infestation rates to analyze the microbiome using next-generation sequencing. We analyzed twenty-four 16S DNA libraries, which resulted in 3278 operational taxonomic units. The alpha and beta diversity of the soil microbiome was similar between sites. In contrast, the larvae from high-density sites presented a higher bacterial gut diversity than larvae from low-density sites, with biomarkers linked to plant digestion, nutrient acquisition, and detoxification. Consequently, larvae from high-density sites displayed several enriched molecular functions associated with the families Ruminococcaceae, Clostridiaceae and Rikenellaceae. These bacteria revealed a supportive function by producing several CAZyme families and other proteins. These findings suggest that the microbiome must be one drive for the increase in P. japonica populations, thus providing a checkpoint in the establishment and spread of this pest.

Chromosome-scale genome assembly of the freshwater cladoceran crustacean Chydorus sphaericus: A resource for discovery of genes responsive to ecological challenges

The genus Chydorus Leach 1816 (family Chydoridae) is a diverse and ecologically important taxon within freshwater ecosystems. Despite having been widely used in ecological, evolutionary and eco-toxicological studies, no high-quality genomic resource is available for any member of the genus. Here, we present a high-quality chromosome-level assembly of the C. sphaericus genome by combining 7.40 Gb (∼ 50 × coverage) PacBio reads, 19.28 Gb (∼ 135 × coverage) Illumina paired-end reads, and 34.04 Gb Hi-C reads. Our genome assembly is approximately 151 Mb, with contig and scaffold N50 lengths of 1.09 Mb and 13.70 Mb, respectively. The assembly captured 94.9% of the complete eukaryotic BUSCO. Repetitive elements accounted for 17.6% of the genome, and 13,549 protein-coding genes were predicted (based on transcriptome sequencing data, ab-initio or homology-based prediction), of which 96.4% have been functionally annotated in the NCBI-NR database. We identified 303 gene families specific to C. sphaericus, mainly families enriched in functions related to immune response, visual senses and detoxification. Interestingly, we also found 53 significantly expanded gene families in C. sphaericus, mostly with functions related to detoxification. This high-quality assembly genome will act as a reference genome for C. sphaericus and benefit studies on functional and comparative genomics of Chydorus and other crustaceans.

Aphid adaptation to cucurbits: sugars, cucurbitacin and phloem structure in resistant and susceptible melons

BACKGROUND

Aphis gossypii, a strictly phloemophagaous aphid, colonize hundreds of plant families, and a group of clones formed a cucurbit-specialised host-race. Cucurbits are unique in having evolved a specific extra-fascicular phloem (EFP), which carries defence-related metabolites such as cucurbitacin, whereas the fascicular phloem (FP) is common to all higher plants and carries primary metabolites, such as raffinose-family oligosaccharides (RFOs). Both cucurbitacins (in the EFP) and galactinol (in the FP) have been suggested to be toxic to aphids. We investigated these hypotheses in cucurbit-specialized A. gossypii fed on melon plants with or without aphid-resistance conferred by the NLR gene Vat. We selected a plant-aphid system with (i) Vat-mediated resistance not triggered, (ii) Vat-mediated resistance triggered by an aphid clone adapted to the presence of Vat resistant alleles and (iii) Vat-mediated resistance triggered by a non-adapted aphid clone.

RESULTS

We quantified cucurbitacin B, its glycosylated derivative, and sugars, in melon plants and aphids that fed on. The level of cucurbitacin in plants was unrelated to both aphid infestation and aphid resistance. Galactinol was present at higher quantities in plants when Vat-mediated resistance was triggered, but its presence did not correlate with aphid performance. Finally, we showed that cucurbit-specialized A. gossypii fed from the FP but could also occasionally access the EFP without sustainably feeding from it. However, the clone not adapted to Vat-mediated resistance were less able to access the FP when the Vat resistance was triggered.

CONCLUSION

We concluded that galactinol accumulation in resistant plants does not affect aphids, but may play a role in aphid adaptation to fasting and that Cucurbitacin in planta is not a real threat to Aphis gossypii. Moreover, the specific phloem of Cucurbits is involved neither in A. gossypii cucurbit specialisation nor in adaptation to Vat-dependent resistance.

Expression profile of the entire detoxification gene inventory of the western honeybee, Apis mellifera across life stages

The western honeybee, Apis mellifera, is a managed pollinator of many crops and potentially exposed to a wide range of foreign compounds, including pesticides throughout its life cycle. Honeybees as well as other insects recruit molecular defense mechanisms to facilitate the detoxification of xenobiotic compounds. The inventory of detoxification genes (DETOXome) is comprised of five protein superfamilies: cytochrome P450 monooxygenases (P450), carboxylesterases, glutathione S-transferases (GST), UDP-glycosyl transferases (UGT) and ATP-binding cassette (ABC) transporters. Here we characterized the gene expression profile of the entire honeybee DETOXome by analyzing 47 transcriptomes across the honeybee life cycle, including different larval instars, pupae, and adults. All life stages were well separated by principal component analysis, and K-means clustering revealed distinct temporal patterns of gene expression. Indeed, >50% of the honeybee detoxification gene inventory is found in one cluster and follows strikingly similar expression profiles, i.e., increased expression during larval development, followed by a sharp decline after pupation and a steep increase again in adults. This cluster includes 29 P450 genes dominated by CYP3 and CYP4 clan members, 15 ABC transporter genes mostly belonging to the ABCC subfamily and 13 carboxylesterase genes including almost all members involved in dietary/detox and hormone/semiochemical processing. RT-qPCR analysis of selected detoxification genes from all families revealed high expression levels in various tissues, especially Malpighian tubules, fatbody and midgut, supporting the view that these tissues are essential for metabolic clearance of environmental toxins and pollutants in honeybees. Our study is meant to spark further research on the molecular basis of detoxification in this critical pollinator to better understand and evaluate negative impacts from potentially toxic substances. Additionally, the entire gene set of 47 transcriptomes collected and analyzed provides a valuable resource for future honeybee research across different disciplines.

A major 6 Mb superlocus is involved in pyrethroid resistance in the common bed bug Cimex lectularius

In the last few years, the bed bug Cimex lectularius has been an increasing problem worldwide, mainly due to the development of insecticide resistance to pyrethroids. The characterization of resistance alleles is a prerequisite to improve surveillance and resistance management. To identify genomic variants associated with pyrethroid resistance in Cimex lectularius, we compared the genetic composition of two recent and resistant populations with that of two ancient-susceptible strains using a genome-wide pool-seq design. We identified a large 6 Mb "superlocus" showing particularly high genetic differentiation and association with the resistance phenotype. This superlocus contained several clustered resistance genes and was also characterized by a high density of structural variants (inversions, duplications). The possibility that this superlocus constitutes a resistance "supergene" that evolved after the clustering of alleles adapted to insecticide and after reduction in recombination is discussed.

Diapause-Linked Gene Expression Pattern and Related Candidate Duplicated Genes of the Mountain Butterfly Parnassius glacialis (Lepidoptera: Papilionidae) Revealed by Comprehensive Transcriptome Profiling

The mountain butterfly Parnassius glacialis is a representative species of the genus Parnassius, which probably originated in the high-altitude Qinhai-Tibet Plateau in the Miocene and later dispersed eastward into relatively low-altitude regions of central to eastern China. However, little is known about the molecular mechanisms underlying the long-term evolutionary adaptation to heterogeneous environmental conditions of this butterfly species. In this study, we obtained the high-throughput RNA-Seq data from twenty-four adult individuals in eight localities, covering nearly all known distributional areas in China, and firstly identified the diapause-linked gene expression pattern that is likely to correlate with local adaptation in adult P. glacialis populations. Secondly, we found a series of pathways responsible for hormone biosynthesis, energy metabolism and immune defense that also exhibited unique enrichment patterns in each group that are probably related to habitat-specific adaptability. Furthermore, we also identified a suite of duplicated genes (including two transposable elements) that are mostly co-expressed to promote the plastic responses to different environmental conditions. Together, these findings can help us to better understand this species' successful colonization to distinct geographic areas from the western to eastern areas of China, and also provide us with some insights into the evolution of diapause in mountain Parnassius butterfly species.

Linkage mapping and genome annotation give novel insights into gene family expansions and regional recombination rate variation in the painted lady (Vanessa cardui) butterfly

Characterization of gene family expansions and crossing over is crucial for understanding how organisms adapt to the environment. Here, we develop a high-density linkage map and detailed genome annotation of the painted lady butterfly (Vanessa cardui) - a non-diapausing, highly polyphagous species famous for its long-distance migratory behavior and almost cosmopolitan distribution. Our results reveal a complex interplay between regional recombination rate variation, gene duplications and transposable element activity shaping the genome structure of the painted lady. We identify several lineage specific gene family expansions. Their functions are mainly associated with protein and fat metabolism, detoxification, and defense against infection - critical processes for the painted lady's unique life-history. Furthermore, the detailed recombination maps allow us to characterize the regional recombination landscape, data that reveal a strong effect of chromosome size on the recombination rate, a limited impact of GC-biased gene conversion and a positive association between recombination and short interspersed elements.

The N-glycosylation-related genes as potential targets for RNAi-mediated pest control of the Colorado potato beetle (Leptinotarsa decemlineata)

BACKGROUND

N-glycosylation is one of the most common and important post-translational modifications in the eukaryotic cell. The study of protein N-glycosylation in several model insects confirmed the importance of this process in insect development, immunity, survival and fertility. The Colorado potato beetle (Leptinotarsa decemlineata) (CPB) is a common pest of Solanaceae crops. With the infamous title of champion of insecticide resistance, novel pest control strategies for this insect are needed. Luckily this pest insect is reported as very sensitive for the post-genomic technology of RNA interference (RNAi).

RESULTS

In this project, we investigated the importance of N-glycosylation in the survival and development of CPB using RNAi-mediated gene silencing of N-glycosylation-related genes (NGRGs) during the different transition steps from the larva, through the pupa to the adult stage. High mortality was observed in the larval stage with the silencing of early NGRGs, as STT3a, DAD1 and GCS1. With dsRNA against middle NGRGs, abnormal phenotypes at the ecdysis process and adult formation were observed, while the silencing of late NGRGs did not cause mortality.

CONCLUSION

The lethal phenotypes observed on silencing of the genes involved in the early processing steps of the N-glycosylation pathway suggest these genes are good candidates for RNAi-mediated control of CPB. Next to the gene-specific mechanism of RNAi for biosafety and possible implementation in integrated pest management, we believe these early NGRGs provide a possible alternative to the well-known target genes Snf7 and vacuolar ATPases that are now used in the first commercial RNAi-based products and thus they may be useful in the context of proactive resistance management. © 2021 Society of Chemical Industry.

Identification and Characterization of UDP-Glycosyltransferase Genes in a Cerambycid Beetle, Pharsalia antennata Gahan, 1894 (Coleoptera: Cerambycidae)

The cerambycid beetle, Pharsalia antennata Gahan, 1894 (Coleoptera: Cerambycidae), is a wood-boring pest that spends most of its life cycle in the trunks or under the bark of trees. These distinctive biological characteristics make it likely that this beetle will encounter a number of plant defensive compounds, coupled with a broad range of host plants, possibly resulting in the overexpression or expansion of uridine diphosphate (UDP)-glycosyltransferase (UGT) genes. Here, we identified and characterized the UGT gene family in P. antennata through transcriptome data, sequence and phylogenetic analyses, and PCR and homology modeling approaches. In total, 59 transcripts encoding UGTs were identified, 34 of which harbored full-length sequences and shared high conservation with the UGTs of Anoplophora glabripennis. Of the 34 PantUGTs, only 31.78% amino acid identity was observed on average, but catalytic and sugar binding residues were highly conserved. Phylogenetic analyses revealed four Cerambycidae-specific clades, including 30 members from P. antennata. Combining the transcriptome and PCR data showed that PantUGTs had a wide tissue expression, and the majority of the genes were presented mainly in antennae or abdomens, suggesting their putative roles in olfaction and detoxification. This study provides, for the first time, information on the molecular and genetic basis of P. antennata, greatly enhancing our knowledge of the detoxification-related UGT gene family.

UDP-Glucosyltransferases Induced by Nosema bombycis Provide Resistance to Microsporidia in Silkworm (Bombyx mori)

Simple Summary

Nosema bombycis (N. bombycis), an obligate intracellular eukaryotic parasite, is a virulent pathogen of the silkworm, that causes major economic losses. Although many studies have reported on B. mori host response to this pathogen, little is known about which genes are induced by N. bombycis. Our results showed that two B. mori uridine diphosphate-glucosyltransferases (UGTs) (BmUGT10295 and BmUGT8453) could be activated by N. bombycis and provide resistance to the microsporidia in silkworms. These results will contribute to our understanding of host stress reaction to pathogens and the two pathogen-induced resistant genes will provide a target for promoting pathogen resistance.

Abstract

As a silkworm pathogen, the microsporidian N. bombycis can be transovarially transmitted from parent to offspring and seriously impedes sericulture industry development. Previous studies found that Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are involved in regulating diverse cellular processes, such as detoxification, pigmentation, and odorant sensing. Our results showed that BmUGT10295 and BmUGT8453 genes were specifically induced in infected silkworms, but other BmUGTs were not. Tissue distribution analysis of the two BmUGTs showed that the transcriptions of the two BmUGTs were mainly activated in the midgut and Malpighian tubule of infected silkworms. Furthermore, there were significantly fewer microsporidia in over-expressed BmUGTs compared with the control, but there were significantly more microsporidia in RNA interference BmUGTs compared with the control. These findings indicate that the two BmUGTs were induced by N. bombycis and provided resistance to the microsporidia.

The UDP-Glycosyltransferase Family in Drosophila melanogaster: Nomenclature Update, Gene Expression and Phylogenetic Analysis

UDP-glycosyltransferases (UGTs) are important conjugation enzymes found in all kingdoms of life, catalyzing a sugar conjugation with small lipophilic compounds and playing a crucial role in detoxification and homeostasis. The UGT gene family is defined by a signature motif in the C-terminal domain where the uridine diphosphate (UDP)-sugar donor binds. UGTs have been identified in a number of insect genomes over the last decade and much progress has been achieved in characterizing their expression patterns and molecular functions. Here, we present an update of the complete repertoire of UGT genes in Drosophila melanogaster and provide a brief overview of the latest research in this model insect. A total of 35 UGT genes are found in the D. melanogaster genome, localized to chromosomes 2 and 3 with a high degree of gene duplications on the chromosome arm 3R. All D. melanogaster UGT genes have now been named in FlyBase according to the unified UGT nomenclature guidelines. A phylogenetic analysis of UGT genes shows lineage-specific gene duplications. Analysis of anatomical and induced gene expression patterns demonstrate that some UGT genes are differentially expressed in various tissues or after environmental treatments. Extended searches of UGT orthologs from 18 additional Drosophila species reveal a diversity of UGT gene numbers and composition. The roles of Drosophila UGTs identified to date are briefly reviewed, and include xenobiotic metabolism, nicotine resistance, olfaction, cold tolerance, sclerotization, pigmentation, and immunity. Together, the updated genomic information and research overview provided herein will aid further research in this developing field.