Knockdown of LmCYP303A1 alters cuticular hydrocarbon profiles and increases the susceptibility to desiccation and insecticides in Locusta migratoria

Matrix metalloproteinase 2 contributes to adult eclosion and immune response in the small hive beetle, Aethina tumida

During the pupal-adult eclosion process of holometabolous insects, the old cuticle is shed and replaced by a completely different new cuticle that requires tanning and expansion, along with extensive extracellular matrix (ECM) remodeling. In vertebrates, matrix metalloproteinases (MMPs), a class of zinc-dependent endopeptidases, play key roles in regulating the ECM that surrounds cells. However, little is known about these extracellular proteinases available in insects. The small hive beetle (SHB), Aethina tumida, is a widespread invasive parasite of honey bees. In this study, 6 MMP homologs were identified in the SHB genome. RNA interference experiments showed that all 6 AtMmps are not required for the larval-pupal transition, only AtMmp2 was essential for pupal-adult eclosion in SHB. Knockdown of AtMmp2 resulted in eclosion defects and wing expansion failure, as well as mortality within 3 d of adult eclosion. Transcriptomic analysis revealed that knockdown of AtMmp2 significantly increased expression of the Toll and Imd pathways, chitin metabolism, and cross-linking (such as the pro-phenoloxidase activating cascade pathway and the tyrosine-mediated cuticle sclerotization and pigmentation pathway). These data revealed evolutionarily conserved functions of Mmp2 in controlling adult eclosion and wing expansion, also provided a preliminary exploration of the novel function of regulating Toll and Imd pathways, as well as new insights into how MMPs regulate insect development and defense barriers.

Nuclear Receptor FTZ-F1 Controls Locust Molt by Regulating the Molting Process of Locusta migratoria

Fushi-tarazu factor 1 (FTZ-F1) is a class of transcription factors belonging to the nuclear receptor superfamily and an important molting regulator in insects; however, its detailed function in the molting process of Locusta migratoria is still unclear. This study identified two FTZ-F1 transcripts (LmFTZ-F1-X1 and LmFTZ-F1-X2) in L. migratoria. The classical domains of FTZ-F1 were present in their protein sequences and distinguished based on their variable N-terminal domains. Reverse-transcription quantitative polymerase chain reaction analysis revealed that LmFTZ-F1-X1 and LmFTZ-F1-X2 were highly expressed in the integument. RNA interference (RNAi) was used to explore the function of LmFTZ-F1s in the molting of the third-instar nymph. Separate LmFTZ-F1-X1 or LmFTZ-F1-X2 silencing did not affect the normal development of third-instar nymphs; however, the simultaneous RNAi of LmFTZ-F1-X1 and LmFTZ-F1-X2 caused the nymphs to be trapped in the third instar stage and finally die. Furthermore, the hematoxylin-eosin and chitin staining of the cuticle showed that the new cuticles were thickened after silencing the LmFTZ-F1s compared to the controls. RNA-seq analysis showed that genes encoding four cuticle proteins, two chitin synthesis enzymes, and cytochrome P450 303a1 were differentially expressed between dsGFP- and dsLmFTZ-F1s-injected groups. Taken together, LmFTZ-F1-X1 and LmFTZ-F1-X2 are involved in the ecdysis of locusts, possibly by regulating the expression of genes involved in cuticle formation, chitin synthesis, and other key molting processes.

Identification and characterization of CYP307A1 as a molecular target for controlling the small hive beetle, Aethina tumida

BACKGROUND

The molting hormone 20-hydroxyecdysone (20E) plays a key role in insect development, metamorphosis, and reproduction. Previous studies have shown that ecdysteroid metabolism is regulated by a series of CYP genes in most of the insect species. However, the roles of these CYP genes in a Coleopteran beetle, Aethina tumida (small hive beetle, SHB) have not yet been explored.

RESULTS

In the current study, we identified seven CYP genes (six Halloween genes and one AtCYP18A1 gene) related to 20E metabolism. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) showed that AtCYP307A1 and AtCYP307B1 were primarily expressed in the embryonic stage and in the cephalothorax of larvae. RNA interference (RNAi) screening revealed that suppression of AtCYP307A1 expression caused a lethal phenotype during the larval-pupal metamorphosis. Furthermore, Hematoxylin and Eosin staining of the integument showed that the RNAi of AtCYP307A1 inhibited the apolysis and degradation of the old cuticle. In addition, silencing of AtCYP307A1 resulted in significant down-regulation of 20E titers and the expression levels of 20E signaling pathway genes. Finally, the AtCYP307A1 RNAi phenotype was rescued by topical application of 20E.

CONCLUSION

Our studies suggest that AtCYP307A1 involved in 20E synthesis is indispensable during the larval-pupal metamorphosis of beetles, which could serve as a putative insecticide target for pest control. © 2022 Society of Chemical Industry.

Clathrin heavy chain is essential for the development and reproduction of Locusta migratoria

Clathrin heavy chain (Chc) is a constituent of clathrin-coated vesicles and serves important functions in endocytosis and intracellular membrane trafficking but appears to have physiological roles also at the organismal level. Most of what we know about Chc functions originates from studies performed in fungal or vertebrate cells. However, the physiological functions of Chc in insects remain poorly understood. Here, we identified a Chc ortholog from a Locusta migratoria transcriptome database. RT-qPCR revealed that LmChc was constitutively expressed in fifth-instar nymphs. In this developmental stage, LmChc showed the highest expression in the ovary followed by hemolymph, testis, hindgut, midgut, and foregut. In isolated hemocytes, we detected the Chc protein in patches at the plasma membrane. To examine the role of LmChc in L. migratoria during development, RNA interference was performed by injecting dsRNA into the early fifth-instar nymphs. Silencing of LmChc caused a lethal phenotype with molting defect from nymph to adult. In addition, silencing of LmChc resulted in abnormal development of the ovaries, the size of which was significantly smaller than that in controls. Taken together, our results suggest that LmChc is a vital gene in L. migratoria that plays an important role in growth, development, and reproduction. LmChc may be used as an efficient RNAi target gene for developing dsRNA-based biological insecticides to manage insect pests.

Functionally characterized arthropod pest and pollinator cytochrome P450s associated with xenobiotic metabolism

The cytochrome P450 family (P450s) of arthropods includes diverse enzymes involved in endogenous essential physiological functions and in the oxidative metabolism of xenobiotics, insecticides and plant allelochemicals. P450s can also establish insecticide selectivity in bees and pollinators. Several arthropod P450s, distributed in different phylogenetic groups, have been associated with xenobiotic metabolism, and some of them have been functionally characterized, using different in vitro and in vivo systems. The purpose of this review is to summarize scientific publications on arthropod P450s from major insect and mite agricultural pests, pollinators and Papilio sp, which have been functionally characterized and shown to metabolize xenobiotics and/or their role (direct or indirect) in pesticide toxicity or resistance has been functionally validated. The phylogenetic relationships among these P450s, the functional systems employed for their characterization and their xenobiotic catalytic properties are presented, in a systematic approach, including critical aspects and limitations. The potential of the primary P450-based metabolic pathway of target and non-target organisms for the development of highly selective insecticides and resistance-breaking formulations may help to improve the efficiency and sustainability of pest control.

Chemical Ecology and Olfaction in Short-Horned Grasshoppers (Orthoptera: Acrididae)

Chemoreception plays a crucial role in the reproduction and survival of insects, which often rely on their sense of smell and taste to find partners, suitable habitats, and food sources, and to avoid predators and noxious substances. There is a substantial body of work investigating the chemoreception and chemical ecology of Diptera (flies) and Lepidoptera (moths and butterflies); but less is known about the Orthoptera (grasshoppers, locusts, crickets, and wēta). Within the Orthoptera, the family Acrididae contains about 6700 species of short-horned grasshoppers. Grasshoppers are fascinating organisms to study due to their significant taxonomic and ecological divergence, however, most chemoreception and chemical ecology studies have focused on locusts because they are agricultural pests (e.g., Schistocerca gregaria and Locusta migratoria). Here we review studies of chemosensory systems and chemical ecology of all short-horned grasshoppers. Applications of genome editing tools and entomopathogenic microorganism to control locusts in association with their chemical ecology are also discussed. Finally, we identify gaps in the current knowledge and suggest topics of interest for future studies.

The Role of Cytochrome P450s in Insect Toxicology and Resistance

Insect cytochrome P450 monooxygenases (P450s) perform a variety of important physiological functions, but it is their role in the detoxification of xenobiotics, such as natural and synthetic insecticides, that is the topic of this review. Recent advances in insect genomics and postgenomic functional approaches have provided an unprecedented opportunity to understand the evolution of insect P450s and their role in insect toxicology. These approaches have also been harnessed to provide new insights into the genomic alterations that lead to insecticide resistance, the mechanisms by which P450s are regulated, and the functional determinants of P450-mediated insecticide resistance. In parallel, an emerging body of work on the role of P450s in defining the sensitivity of beneficial insects to insecticides has been developed. The knowledge gained from these studies has applications for the management of P450-mediated resistance in insect pests and can be leveraged to safeguard the health of important beneficial insects.

Involvement of CYP2 and mitochondrial clan P450s of Helicoverpa armigera in xenobiotic metabolism

Insect CYP2 and mitochondrial clan P450s are relatively conserved genes encoding enzymes generally thought to be involved in biosynthesis or metabolism of endobiotics. However, emerging evidence argues they have potential roles in chemical defense as well, but their actual detoxification functions remain largely unknown. Here, we focused on the full complement of 8 CYP2 and 10 mitochondrial P450s in the generalist herbivore, Helicoverpa armigera. Their varied spatiotemporal expression profiles were analyzed and reflected their specific functions. For functional study of the mitochondrial clan P450s, the redox partners, adrenodoxin reductase (AdR) and adrenodoxin (Adx), were identified from genomes of eight insects and an efficient in vitro electron transfer system of mitochondrial P450 was established by co-expression with Adx and AdR of H. armigera. All CYP2 clan P450s and 8 mitochondrial P450s were successfully expressed in Sf9 cells and compared functionally. In vitro metabolism assays showed that two CYP2 clan P450s (CYP305B1 and CYP18A1) and CYP333B3 (mito clan) could epoxidize aldrin to dieldrin, while CYP305B1 and CYP339A1 (mito clan) have limited but significant hydroxylation capacities to esfenvalerate. CYP303A1 of the CYP2 clan exhibits high metabolic efficiency to 2-tridecanone. Screening the xenobiotic metabolism competence of CYP2 and mitochondrial clan P450s not only provides new insights on insect chemical defense but also can give indications on their physiological functions in H. armigera and other insects.

CYP4G8 is responsible for the synthesis of methyl-branched hydrocarbons in the polyphagous caterpillar of Helicoverpa armigera

Insect cuticular hydrocarbons (CHCs) have dual functions as physical barrier and chemical signals. The last step of CHC biosynthesis is known to be catalyzed by cytochrome P450 CYP4G in a number of insects. Until recently, studies on CYP4Gs in the context of functional evolution are rare. In this study, we analyzed sequence similarity and temporal-spatial expression patterns of the five CYP4G genes in the cotton bollworm Helicoverpa armigera, an important agricultural pest and also typical representative of lepidopteran insects. Moreover, the CRISPR/Cas9-induced knockout was used to clarify the roles of the five CYP4Gs in CHC biosynthesis. Temporal-spatial expression patterns revealed that CYP4G8 was highly expressed at all developmental stages and in most tissues examined. Larvae with CYP4G8 knocked out could not produce methyl-branched CHCs and failed to pupate, while larvae with the other four CYP4G genes knocked out (4G1-type-KO) showed no significant changes in their CHC profiles, weight gain and survival. Comparative transcriptomics revealed that knocking out CYP4G8 affected the global gene expression in larvae, especially down-regulated the expression of genes in the fatty acid biosynthetic pathway, while no significant change in 4G1-type-KO transcriptome was observed. These findings indicate that the five members of the CYP4G subfamily have undergone functional divergence: CYP4G8 maintains the essential function in CHC biosynthesis, while the function of the other four CYP4G genes remains unclear. Intriguingly, CYP4G8 has evolved to be a P450 enzyme responsible for the synthesis of larval methyl-branched hydrocarbons. The observation that CYP4G8 knockout is lethal strongly suggest that CYP4G8 may serve as a candidate target for the development of insecticidal agents for the control of cotton bollworms.

Detoxification gene families in Phylloxera: Endogenous functions and roles in response to the environment

Phylloxera, Daktulosphaira vitifoliae, is an agronomic pest that feeds monophagously on grapevine, Vitis spp. host plants. Phylloxera manipulates primary and secondary plant metabolism to establish either leaf or root galls. We manually annotated 198 detoxification genes potentially involved in plant host manipulation, including cytochrome P450 (66 CYPs), carboxylesterase (20 CCEs), glutathione-S-transferase (10 GSTs), uridine diphosphate-glycosyltransferase (35 UGTs) and ABC transporter (67 ABCs) families. Transcriptomic expression patterns of these detoxification genes were analyzed for root and leaf galls. In addition to these transcriptomic analyses, we reanalyzed recent data from L1 and L2-3 stages feeding on tolerant and resistant rootstock. Data from two agricultural pest aphids, the generalist Myzus persicae and the Fabaceae specialist Acyrthosiphon pisum, and from the true bug vector of Chagas disease, Rhodnius prolixus, were used to perform phylogenetic analyses for each detoxification gene family. We found expansions of several gene sub-families in the genome of D. vitifoliae. Phylogenetically close genes were found to be organized in clusters in the same genomic position and orientation suggesting recent successive duplications. These results highlight the roles of the phylloxera detoxification gene repertoire in insect physiology and in adaptation to plant secondary metabolites, and provide gene candidates for further functional analyses.

Cytochrome P450s Are Essential for Insecticide Tolerance in the Endoparasitoid Wasp Meteorus pulchricornis (Hymenoptera: Braconidae)

With the widespread application of insecticides, parasitoid wasps may also be under risk when exposed to insecticides directly at their free-living stages. The endoparasitoid wasp Meteorus pulchricornis is the predominant natural enemy of many lepidopteran pests, such as Spodoptera litura and Helicoverpa armigera. The cytochrome P450 monooxygenases constitute a ubiquitous and complex superfamily of hydrophobic, haem-containing enzymes. P450s are involved in the detoxification of many xenobiotics. However, their exact roles in the tolerance mechanism in parasitoids toward insecticides has received less attention. Here, 28 P450 genes in M. pulchricornis were identified from a previously constructed transcriptome dataset. These P450 genes belonged to CYP2, -3, and -4, and mitochondrial clans. Subsequently, eight candidate MpulCYPs were selected from four CYP clans to validate their expression patterns under phoxim, cypermethrin, and chlorfenapyr exposure by qRT-PCR. The results showed that all three insecticides had significant effects on the expression of MpulCYPs. To further study the function of P450s, CYP369B3 was silenced, and its expression levels of CYP369B3 were significantly decreased. Survival analysis indicated that after dsRNA injection, the mortality rate of wasps was significantly increased when M. pulchricornis females were exposed to insecticides compared to control groups. Our findings provide a theoretical base for elucidating the mechanism of insecticide tolerance and promote functional research on P450 genes in parasitoid wasps.

Diversity and evolution of the P450 family in arthropods

The P450 family (CYP genes) of arthropods encodes diverse enzymes involved in the metabolism of foreign compounds and in essential endocrine or ecophysiological functions. The P450 sequences (CYPome) from 40 arthropod species were manually curated, including 31 complete CYPomes, and a maximum likelihood phylogeny of nearly 3000 sequences is presented. Arthropod CYPomes are assembled from members of six CYP clans of variable size, the CYP2, CYP3, CYP4 and mitochondrial clans, as well as the CYP20 and CYP16 clans that are not found in Neoptera. CYPome sizes vary from two dozen genes in some parasitic species to over 200 in species as diverse as collembolans or ticks. CYPomes are comprised of few CYP families with many genes and many CYP families with few genes, and this distribution is the result of dynamic birth and death processes. Lineage-specific expansions or blooms are found throughout the phylogeny and often result in genomic clusters that appear to form a reservoir of catalytic diversity maintained as heritable units. Among the many P450s with physiological functions, six CYP families are involved in ecdysteroid metabolism. However, five so-called Halloween genes are not universally represented and do not constitute the unique pathway of ecdysteroid biosynthesis. The diversity of arthropod CYPomes has only partially been uncovered to date and many P450s with physiological functions regulating the synthesis and degradation of endogenous signal molecules (including ecdysteroids) and semiochemicals (including pheromones and defense chemicals) remain to be discovered. Sequence diversity of arthropod P450s is extreme, and P450 sequences lacking the universally conserved Cys ligand to the heme have evolved several times. A better understanding of P450 evolution is needed to discern the relative contributions of stochastic processes and adaptive processes in shaping the size and diversity of CYPomes.