Expansion of cytochrome P450 and cathepsin genes in the generalist herbivore brown marmorated stink bug

Genome-wide identification, molecular evolution and gene expression of P450 gene family in Cyrtotrachelus buqueti

BACKGROUND

Insect Cytochrome P450 monooxygenase (CYPs or P450s) plays an important role in detoxifying insecticides, causing insect populations to develop resistance. However, the molecular functions of P450 gene family in Cyrtotrachelus buqueti genome are still lacking.

RESULTS

In this study, 71 CbuP450 genes have been identified. The amino acids length of CbuP450 proteins was between 183 aa ~ 1041 aa. They are proteins with transmembrane domains. The main component of their secondary structure is α-helix and random coils. Phylogenetic analysis showed that C. buqueti and Rhynchophorus ferrugineus were the most closely related. This gene family has 29 high-frequency codons, which tend to use A/T bases and A/T ending codons. Gene expression analysis showed that CbuP450_23 in the female adult may play an important role on high temperature resistance, and CbuP450_17 in the larval may play an important role on low temperature tolerance. CbuP450_10, CbuP450_17, CbuP450_23, CbuP450_10, CbuP450_16, CbuP450_20, CbuP450_23 and CbuP450_ 29 may be related to the regulation of bamboo fiber degradation genes in C. buqueti. Protein interaction analysis indicates that most CbuP450 proteins are mainly divided into three aspects: encoding the biosynthesis of ecdysteroids, participating in the decomposition of synthetic insecticides, metabolizing insect hormones, and participating in the detoxification of compounds.

CONCLUSIONS

We systematically analyzed the gene and protein characteristics, gene expression, and protein interactions of CbuP450 gene family, revealing the key genes involved in the stress response of CbuP450 gene family in the resistance of C. buqueti to high or low temperature stress, and identified the key CbuP450 proteins involved in important life activity metabolism. These results provided a reference for further research on the function of P450 gene family in C. buqueti.

Identification of metabolizing enzyme genes associated with xenobiotics and odorants in the predatory stink bug Arma custos based on transcriptome analysis

The predatory stink bug, Arma custos, is a highly effective beneficial predator of crop pests. The lack of gene information related to xenobiotic detoxification and odorant degrading enzymes in the predator stink bugs to date has limited our ability for more in-depth studies of biological control. Hence, we conducted de novo assembly of the A. custos transcriptome from guts, antennae, and other tiussue samples of 5th instar larvae using Illumina sequencing technology. A total of 91, 50 and 23 genes of cytochrome P450 monooxygenases (CYPs), carboxyl/choline esterases (CCEs) and glutathione S-transferases (GSTs) genes were identified, respectively. Gene expansions of CYP3 and CYP4 clans and the hormone and pheromone processing CCE class were found in A. custos. Analysis of tissue-specific expression patterns showed that 37 CYPs, 14 CCEs and 8 GSTs were enriched in guts, and 6 CYPs, 5 CCEs and 2 GSTs were up-regulated in antennae, suggesting their potential roles on xenobiotics detoxification and ordorant degradation. Gene information data presented here could be useful for a deeper understanding of the ecology, physiology and behavior of this beneficial species and could be helpful to improve their bio-control efficiency.

Effects of Methyl Jasmonate Fumigation on the Growth and Detoxification Ability of Spodoptera litura to Xanthotoxin

Methyl jasmonate (MeJA) is a volatile substance derived from jasmonic acid (JA), and it responds to interbiotic and abiotic stresses by participating in interplant communication. Despite its function in interplant communication, the specific role of MeJA in insect defense responses is poorly understood. In this study, we found that carboxylesterase (CarE) activities, glutathione-S-transferase (GSTs) activities, and cytochrome mono-oxygenases (P450s) content increased more after the feeding of diets containing xanthotoxin, while larvae exposed to MeJA fumigation also showed higher enzyme activity in a dose-dependent manner: lower and medium concentrations of MeJA induced higher detoxification enzyme activities than higher concentrations of MeJA. Moreover, MeJA improved the growth of larvae fed on the control diet without toxins and diets with lower concentrations of xanthotoxin (0.05%); however, MeJA could not protect the larvae against higher concentrations of xanthotoxin (0.1%, 0.2%). In summary, we demonstrated that MeJA is effective at inducing S. litura defense response, but the enhanced detoxifying ability could not overcome the strong toxins.

Gut transcriptome analysis of P450 genes and cytochrome P450 reductase in three moth species feeding on gymnosperms or angiosperms

Cytochrome P450 enzymes (P450s, CYPs) are a superfamily of heme–thiolate proteins involved in the metabolism of endogenous and exogenous substances in insects. In this study, the identification of putative P450 proteins was done and the elimination of the repeated sequences resulted in 57 proteins from Gastropacha populifolia, 63 proteins from Dendrolimus punctatus, and 53 proteins from Dendrolimus tabulaeformis. The putative P450 proteins were aligned together with seven other insect species based on five conserved domains. A total of ten co-orthologous groups were identified. Interestingly, one co-orthologous gene, CYP4g15 in CYP4 clan, was identified and its 3D structure analysis showed that the highly conserved sites of the predicted motifs were close to the active sites of P450. Furthermore, this study revealed that insect CYP4g15 and two bacteria cytochrome P450 were monophyletic. This suggests that insects CYP4g15 are not only functionally conserved but also an ancient gene originating from different bacteria species.

A full-length transcriptome and gene expression analysis of three detoxification gene families in a predatory stink bug, Picromerus lewisi

The predatory stink bug P. Lewisi shows potential for Integrated Pest Management programs for controlling Lepidoptera pest insects in crops and forests. The importance of this insect for biological control has stimulated several studies into its biology and ecology. However, P. lewisi has little genetic information available. In the present study, PacBio single-molecule real-time (SMRT) sequencing and Illumina RNA-seq sequencing technologies were used to reveal the full-length transcriptome profiling and tissue-specific expression patterns of P. lewisi. A total of 12,997 high-quality transcripts with an average length of 2,292 bp were obtained from different stages of P. lewisi using SMRT sequencing. Among these, 12,101 were successfully annotated in seven public databases. A total of 67 genes of cytochrome P450 monooxygenases, 43 carboxylesterase genes, and 18 glutathione S-transferase genes were identified, most of which were obtained with full-length ORFs. Then, tissue-specific expression patterns of 5th instar nymphs were analyzed using Illumina sequencing. Several candidate genes related to detoxification of insecticides and other xenobiotics as well as the degradation of odors, were identified in the guts and antennae of P. lewisi. The current study offered in-depth knowledge to understand the biology and ecology of this beneficial predator and related species.

Cytochrome P450 Genes Expressed in Phasmatodea Midguts

Cytochrome P450s (CYPs) are xenobiotic detoxification genes found in most eukaryotes, and linked in insects to the tolerance of plant secondary chemicals and insecticide resistance. The number and diversity of CYP clans, families, and subfamilies that an organism produces could correlate with its dietary breadth or specialization. This study examined the CYP diversity expressed in the midguts of six species of folivorous stick insects (Phasmatodea), to identify their CYP complement and see if any CYPs correlate with diet toxicity or specialization, and see what factors influenced their evolution in this insect order. CYP genes were mined from six published Phasmatodea transcriptomes and analyzed phylogenetically. The Phasmatodea CYP complement resembles that of other insects, though with relatively low numbers, and with significant expansions in the CYP clades 6J1, 6A13/14, 4C1, and 15A1. The CYP6 group is known to be the dominant CYP family in insects, but most insects have no more than one CYP15 gene, so the function of the multiple CYP15A1 genes in Phasmatodea is unknown, with neofunctionalization following gene duplication hypothesized. No correlation was found between CYPs and diet specialization or toxicity, with some CYP clades expanding within the Phasmatodea and others likely inherited from a common ancestor.

Review: Trait plasticity during plant-insect interactions: From molecular mechanisms to impact on community dynamics

Phenotypic plasticity, prevalent in all domains of life, enables organisms to cope with unpredictable or novel changes in their growing environment. Plants represent an interesting example of phenotypic plasticity which also directly represents and affects the dynamics of biological interactions occurring in a community. Insects, which interact with plants, manifest phenotypic plasticity in their developmental, physiological, morphological or behavioral traits in response to the various host plant defenses induced upon herbivory. However, plant-insect interactions are generally more complex and multidimensional because of their dynamic association with their respective microbiomes and macrobiomes. Moreover, these associations can alter plant and insect responses towards each other by modulating the degree of phenotypic plasticity in their various traits and studying them will provide insights into how plants and insects reciprocally affect each other's evolutionary trajectory. Further, we explore the consequences of phenotypic plasticity on relationships and interactions between plants and insects and its impact on their development, evolution, speciation and ecological organization. This overview, obtained after exploring and comparing data obtained from several inter-disciplinary studies, reveals how genetic and molecular mechanisms, underlying plasticity in traits, impact species interactions at the community level and also identifies mechanisms that could be exploited in breeding programs.

Host-specific gene expression as a tool for introduction success in Naupactus parthenogenetic weevils

Food resource access can mediate establishment success in invasive species, and generalist herbivorous insects are thought to rely on mechanisms of transcriptional plasticity to respond to dietary variation. While asexually reproducing invasives typically have low genetic variation, the twofold reproductive capacity of asexual organisms is a marked advantage for colonization. We studied host-related transcriptional acclimation in parthenogenetic, invasive, and polyphagous weevils: Naupactus cervinus and N. leucoloma. We analyzed patterns of gene expression in three gene categories that can mediate weevil-host plant interactions through identification of suitable host plants, short-term acclimation to host plant defenses, and long-term adaptation to host plant defenses and their pathogens. This approach employed comparative transcriptomic methods to investigate differentially expressed host detection, detoxification, immune defense genes, and pathway-level gene set enrichment. Our results show that weevil gene expression responses can be host plant-specific, and that elements of that response can be maintained in the offspring. Some host plant groups, such as legumes, appear to be more taxing as they elicit a complex gene expression response which is both strong in intensity and specific in identity. However, the weevil response to taxing host plants shares many differentially expressed genes with other stressful situations, such as host plant cultivation conditions and transition to novel host, suggesting that there is an evolutionarily favorable shared gene expression regime for responding to different types of stressful situations. Modulating gene expression in the absence of other avenues for phenotypic adaptation may be an important mechanism of successful colonization for these introduced insects.

Proteases inhibitors-insensitive cysteine proteases allow Nezara viridula to feed on growing seeds of field-grown soybean

The southern green stink bug, Nezara viridula is one of the primary soybean pests and causes significant economic losses around the world. In spite of the high proteases inhibitor (PI) levels, N. viridula can feed on developing seeds of field-grown soybean and reduce crop yields. Although the PI-induced responses have been extensively investigated in many pest insects, there is lack of knowledge about the mechanisms that stink bugs employ to withstand cysteine PIs of soybean seeds. This study demonstrated that feeding on developing seeds of field-grown soybean inhibited total proteases activity of N. viridula, as result of inhibition of cathepsin B-like activity in the gut. In addition, from the 30 digestive cathepsins recognized in this study, 6 were identified as cathepsin B-like. Stink bugs that fed on growing seeds of field-grown soybean had similar gut pH to those reared in the laboratory, and both cathepsin B- and L-like had an optima pH of 6.5. Therefore, using specific proteases inhibitors we found that the main proteolytic activity in the gut is from cysteine proteases when N. viridula feeds on soybean crops. Since cathepsin L-like activity was not inhibited by soybean PIs, our results suggested that N. viridula relays on cathepsin L-like to feed on soybean. To our knowledge no study before has shown the impact of seed PIs of field-grown soybean on digestive proteases (cathepsin B- and L-like) of N. viridula. This study suggests that the activity of PI-insensitive cathepsins L-like in the gut would be part of an adaptive strategy to feed on developing soybean seeds. In agreement, the expansions of cathepsin L-like complement observed in pentatomids could confer to the insects a higher versatility to counteract the effects of different PIs.

Cathepsins L and B in Dysdercus peruvianus, Rhodnius prolixus, and Mahanarva fimbriolata. Looking for enzyme adaptations to digestion

Cysteine peptidases (CP) play a role as digestive enzymes in hemipterans similar to serine peptidases in most other insects. There are two major CPs: cathepsin L (CAL), which is an endopeptidase and cathepsin B (CAB) that is both an exopeptidase and a minor endopeptidase. There are thirteen putative CALs in Dysdercus peruvianus, which in some cases were confirmed by cloning their encoding genes. RNA-seq data showed that DpCAL5 is mainly expressed in the anterior midgut (AM), DpCAL10 in carcass (whole body less midgut), suggesting it is a lysosomal enzyme, and the other DpCALs are expressed in middle (MM) and posterior (PM) midgut. The expression data were confirmed by qPCR and enzyme secretion to midgut lumen by a proteomic approach. Two CAL activities were isolated by chromatography from midgut samples with similar kinetic properties toward small substrates. Docking analysis of a long peptide with several DpCALs modeled with digestive Tenebrio molitor CAL (TmCAL3) as template showed that on adapting to luminal digestion DpCALs (chiefly DpCAL5) changed in relation to their ancestral lysosomal enzyme (DpCAL10) mainly at its S2 subsite. A similar conclusion arrived from structure alignment-based clustering of DpCALs based on structural similarity of the modeled structures. Changes mostly on S2 subsite could mean the enzymes turn out less peptide-bond selective, as described in TmCALs. R. prolixus CALs changed on adapting to luminal digestion, although less than DpCALs. Both D. peruvianus and R. prolixus have two digestive CABs which are expressed in the same extension as CALs, in the first digestive section of the midgut, but less than in the other midgut sections. Mahanarva fimbriolata does not seem to have digestive CALs and their digestive CABs are mainly expressed in the first digestive section of the midgut and do not diverge much from their lysosomal counterparts. The data suggest that CABs are necessary at the initial stage of digestion in CP-dependent Hemipterans, which action is completed by CALs with low peptide-bond selectivity in Heteroptera species. In M. fimbriolata protein digestion is supposed to be associated with the inactivation of sap noxious proteins, making CAB sufficient as digestive CP. Hemipteran genomes and transcriptome data showed that CALs have been recruited as digestive enzymes only in heteropterans, whereas digestive CABs occur in all hemipterans.

A transcriptomic and proteomic atlas of expression in the Nezara viridula (Heteroptera: Pentatomidae) midgut suggests the compartmentalization of xenobiotic metabolism and nutrient digestion

BACKGROUND

Stink bugs are an emerging threat to crop security in many parts of the globe, but there are few genetic resources available to study their physiology at a molecular level. This is especially true for tissues such as the midgut, which forms the barrier between ingested material and the inside of the body.

RESULTS

Here, we focus on the midgut of the southern green stink bug Nezara viridula and use both transcriptomic and proteomic approaches to create an atlas of expression along the four compartments of the anterior-posterior axis. Estimates of the transcriptome completeness were high, which led us to compare our predicted gene set to other related stink bugs and Hemiptera, finding a high number of species-specific genes in N. viridula. To understand midgut function, gene ontology and gene family enrichment analyses were performed for the most highly expressed and specific genes in each midgut compartment. These data suggested a role for the anterior midgut (regions M1-M3) in digestion and xenobiotic metabolism, while the most posterior compartment (M4) was enriched in transmembrane proteins. A more detailed characterization of these findings was undertaken by identifying individual members of the cytochrome P450 superfamily and nutrient transporters thought to absorb amino acids or sugars.

CONCLUSIONS

These findings represent an initial step to understand the compartmentalization and physiology of the N. viridula midgut at a genetic level. Future studies will be able to build on this work and explore the molecular physiology of the stink bug midgut.

Proteases and nucleases across midgut tissues of Nezara viridula (Hemiptera:Pentatomidae) display distinct activity profiles that are conserved through life stages

The southern green stink bug, Nezara viridula is a polyphagous pest of commercially important crops during both nymph and adult stages. This insect has recently transitioned from a secondary agricultural pest to one of primary concern. Novel management solutions are needed due to the limited effectiveness of current control strategies. We performed biochemical and transcriptomic analyses to characterize digestive enzymes in the salivary glands and along midgut tissues of N. viridula nymphs and adults fed on sweet corn. The digestive profiles were more distinct between midgut regions (M1 to M3) than between life stages. Aminopeptidase and chymotrypsin activities declined from the M1 (anterior) toward the M3 midgut region. Cysteine protease activity was higher in the M2 and M3 regions than in M1. Differences in sensitivity to chymotrypsin inhibitors between midgut regions suggest that distinct genes or isoforms are expressed in different regions of the gut. In nymphs, DNA and RNA degradation was higher in M1 than in M3. Adult nuclease activity was low across all midgut regions, but high in salivary glands. The differences in protease activities are reflected by transcriptomic data and functional enrichment of GO terms. Together, our results show that different regions of the digestive tract of N. viridula have specific and distinct digestive properties, and increase our understanding of the physiology of this organism.

Differential Expression of Cytochrome P450 CYP6 Genes in the Brown Marmorated Stink Bug, Halyomorpha halys (Hemiptera: Pentatomidae)

Cytochrome (CYP) P450s are a superfamily of enzymes that detoxify xenobiotics and regulate numerous physiological processes in insects. The genomes of phytophagous insects usually contain large numbers of P450s, especially within the CYP3 clan. Within this clan, CYP6 subfamily members help detoxify plant host secondary metabolites. In this study, we analyzed three CYP6 genes in the highly polyphagous invasive pest, Halyomorpha halys (Stål), commonly known as brown marmorated stink bug. We characterized and validated the expression of HhCYP6BQ27, HhCYP6BK13, and HhCYP6BK24 among sexes, tissues (gut, fat body, and Malpighian tubules) and hosts (apple, corn, soybean). Sequence characterization by amino acid alignments confirmed the presence of conserved motifs typical of the P450 superfamily. No significant differences existed in gene expression among sexes or when fed different hosts, suggesting that these transcripts might have broad substrate specificities. However, significant differences in gene expression were observed among the tissues studied and were gene-dependent. Collectively, the results show that H. halys differentially expressed CYP6 genes among tissues, which may be related to important and specific physiological functions. This study has increased our understanding of H. halys biology that can be useful for functional studies and can potentially be exploited in developing sustainable pest management strategies.

Genome Size Reversely Correlates With Host Plant Range in Helicoverpa Species

In organisms with very low percentages of transposable elements (TEs), genome size may positively or negatively correlate with host range, depending on whether host adaptation or host modification is the main route to host generalism. To test if this holds true for insect herbivores with greater percentages of TEs, we conducted flow cytometry to measure the endopolyploidy levels and C-values of the host modification (salivary gland and mandibular gland in head), host adaptation (midgut), and host use-independent tissues (male gonad, hemolymph, and Malpighian tubules) of the generalist Helicoverpa armigera and the head of its older specialist sister H. assulta. Larval salivary gland displayed a consecutive chain of endopolyploidy particles from 8Cx to higher than 32Cx and larval head and midgut had endopolyploidy nuclei clusters of 16Cx and 32Cx, whereas larval male gonad, hemolymph, and Malpighian tubules possessed no endopolyploidy nuclei of higher than 8Cx. The estimated genome size of the Solanaceae plant specialist H. assulta is 430 Mb, significantly larger than that of its older generalist sister Heliothis virescens (408 Mb) and those of its two generalist descendants H. armigera (394 Mb) and H. zea (363 Mb). These data not only reveal a negative correlation between host plant range and genome size in this terminal lineage, but also imply that Helicoverpa species appear to depend more on host modification than on host adaptation to achieve polyphagy.

Tissue-specific transcription of proteases and nucleases across the accessory salivary gland, principal salivary gland and gut of Nezara viridula

The phytophagous stink bug, Nezara viridula (L.) infests multiple plant species and impacts agricultural production worldwide. We analyzed the transcriptomes of N. viridula accessory salivary gland (ASG), principal salivary gland (PSG) and gut, with a focus on putative digestive proteases and nucleases that present a primary obstacle for the stability of protein- or nucleic acid-based stink bug control approaches. We performed high throughput Illumina sequencing followed by de novo transcriptome assemblies. We identified the sequences of 141 unique proteases and 134 nucleases from the N. viridula transcriptomes. Analysis of relative transcript abundance in conjunction with previously reported proteome data (Lomate and Bonning, 2016) supports high levels of serine protease expression in the salivary glands and high cysteine protease expression in the gut. Specifically, trypsin and chymotrypsin transcripts were abundant in the PSG, and cathepsin L-like cysteine protease transcripts were abundant in the gut. Nuclease transcript levels were generally lower than those of the proteases, the exception being abundant transcripts of ribonuclease-C20 in the PSG. The abundance of chymotrypsin, trypsin, and some carboxypeptidase transcripts suggests a significant role for the PSG in production of digestive enzymes. This result is at odds with the premise that the ASG produces watery saliva, which is high in enzymatic activity, while the PSG produces only sheath saliva. We have generated a comprehensive transcriptome sequence dataset from the digestive organs of N. viridula, identified major protease and nuclease genes and confirmed expression of the most abundant enzymes thereby providing greater insight into the digestive physiology of N. viridula.

CYP6AE gene cluster knockout in Helicoverpa armigera reveals role in detoxification of phytochemicals and insecticides

The cotton bollworm Helicoverpa armigera, is one of the world's major pest of agriculture, feeding on over 300 hosts in 68 plant families. Resistance cases to most insecticide classes have been reported for this insect. Management of this pest in agroecosystems relies on a better understanding of how it copes with phytochemical or synthetic toxins. We have used genome editing to knock out a cluster of nine P450 genes and show that this significantly reduces the survival rate of the insect when exposed to two classes of host plant chemicals and two classes of insecticides. Functional expression of all members of this gene cluster identified the P450 enzymes capable of metabolism of these xenobiotics. The CRISPR-Cas9-based reverse genetics approach in conjunction with in vitro metabolism can rapidly identify the contributions of insect P450s in xenobiotic detoxification and serve to identify candidate genes for insecticide resistance.

New views on the Malpighian tubule from post-genomic technologies

Successful insect diversification depends at least in part on the ability to osmoregulate successfully across a broad range of ecological niches. First described in the 17th Century, and Malpighian tubules have been studied physiologically for 70 years. However, our understanding has been revolutionized by the advent of genomics, transcriptomics, proteomics and metabolomics. Such technologies are natural partners with (though do not obligatorily require) model organisms and transgenic technologies. This review describes the recent impact of multi-omic technologies on our understanding or renal function and control in insects.