The fatty acid elongase gene LmELO7 is required for hydrocarbon biosynthesis and cuticle permeability in the migratory locust, Locusta migratoria

The ATP-binding cassette transporter subfamily G member 4 mediates cuticular hydrocarbon transport to regulate drought tolerance in Acyrthosiphon pisum

ABC transporters are a highly conserved membrane protein class that promote the transport of substances across membranes. Under drought conditions, insects primarily regulate the content of cuticular hydrocarbon (CHC) to retain water and prevent evaporative loss. Involvement of ABC transporter protein G (ABCG) subfamily genes in insect CHC transport has been relatively understudied. In this study, we demonstrated that ABCG4 gene in Acyrthosiphon pisum (ApABCG4) is involved in CHC transport and affects drought tolerance by regulating CHC accumulation. ApABCG4 is strongly expressed in the abdominal cuticle and embryonic stages of A. pisum. Effective silencing of ApABCG4 was achieved using RNAi, and the silencing duration was analyzed. ApABCG4 silencing resulted in a significant decrease in the total and component contents of the CHC and cuticular waxy coatings of A. pisum. Nevertheless, the internal hydrocarbon content remained unchanged. The lack of cuticular hydrocarbons significantly reduced the drought tolerance of A. pisum, shortening its survival time under drought stress. Drought stress caused significant upregulation of ApABCG4. Molecular docking showed that ApABCG4 has a high binding affinity for nine n-alkanes of CHC through electrostatic interactions. These results indicate that ApABCG4 is a novel RNAi target with key applications in aphid biological control.

Genome-wide identification and molecular evolution of elongation family of very long chain fatty acids proteins in Cyrtotrachelus buqueti

To reveal the molecular function of elongation family of very long chain fatty acids(ELO) protein in Cyrtotrachelus buqueti, we have identified 15 ELO proteins from C.buqueti genome. 15 CbuELO proteins were located on four chromosomes. Their isoelectric points ranged from 9.22 to 9.68, and they were alkaline. These CbuELO proteins were stable and hydrophobic. CbuELO proteins had transmembrane movement, and had multiple phosphorylation sites. The secondary structure of CbuELO proteins was mainly α-helix. A total of 10 conserved motifs were identified in CbuELO protein family. Phylogenetic analysis showed that molecular evolutionary relationships of ELO protein family between C. buqueti and Tribolium castaneum was the closest. Developmental transcriptome analysis indicated that CbuELO10, CbuELO13 and CbuELO02 genes were key enzyme genes that determine the synthesis of very long chain fatty acids in pupae and eggs, CbuELO6 and CbuELO7 were that in the male, and CbuELO8 and CbuELO11 were that in the larva. Transcriptome analysis under different temperature conditions indicated that CbuELO1, CbuELO5, CbuELO12 and CbuELO14 participated in regulating temperature stress responses. Transcriptome analysis at different feeding times showed CbuELO12 gene expression level in all feeding time periods was significant downregulation. The qRT-PCR experiment verified expression level changes of CbuELO gene family under different temperature and feeding time conditions. Protein-protein interaction analysis showed that 9 CbuELO proteins were related to each other, CbuELO1, CbuELO4 and CbuELO12 had more than one interaction relationship. These results lay a theoretical foundation for further studying its molecular function during growth and development of C. buqueti.

Fatty Acid Elongase Gene PcELO7 is Essential for Lipid Accumulation and Fecundity of Panonychus citri (Acari: Tetranychidae)

RNA interference (RNAi) has been proposed as a promising strategy for sustainable and ecofriendly pest control. The insect cuticle lipids were deposited on the body surface and functioned as a defense against chemical xenobiotics. They consisted of aliphatic compounds, including free fatty acids (FFAs). However, elongase of very long chain fatty acids (ELOs) is essential for FFA biosynthesis; the function of ELO is still unknown in many arthropods, including Panonychus citri (P. citri). In this study, three ELOs were cloned. Developmental-specific mRNA expression results revealed that three PcELOs were highly expressed in egg and adult females. Whereas PcELO7 was dominantly expressed in adult females. Under spirobudiclofen stress, ELOs mRNA expression had different changes, and PcELO7 was down-regulated. The silencing of PcELO7 resulted in a dramatic reduction of oviposition and hatchability. Significant reduction of FFA contents was also examined within PcELO7-repressed P. citri. In addition, we found that PcELO7 mRNA levels were related to fecundity and could affect triacylglycerol (TG) contents. The findings demonstrated that the introduction of dsPcELO7 via oral feeding induced the RNA interference-mediated silencing of a special target gene and could result in mortality and reproduction. In conclusion, PcELO7 is a special RNAi target for P. citri control, and its lethal mechanism might be disturbing lipids biosynthesis.

Knockdown of the ABCG23 Gene Disrupts the Development and Lipid Accumulation of Panonychus citri (Acari/Tetranychidae)

Panonychus citri is a worldwide citrus pest that is currently controlled through the use of insecticides. However, alternative strategies are required to manage P. citri. Recent studies suggest that the ATP-binding cassette (ABC) transporter G subfamily plays a crucial role in transporting cuticular lipids, which are essential for the insect's barrier function against microbial penetration. Therefore, investigating the potential of the ABC transporter G subfamily as a control measure for P. citri could be a promising approach. Based on the genome database, the gene was cloned, and the transcriptional response of ABCG23 for the different developmental stages of P. citri and under spirobudiclofen stress was investigated. Our results showed that the expression level of ABCG23 was significantly lower in adult females exposed to treatment compared to the control and was higher in females than males. The knockdown of ABCG23 using RNAi led to a decrease in the survival rate, fecundity, and TG contents of P. citri. Additionally, a lethal phenotype was characterized by body wrinkling and darkening. These results indicate that ABCG23 may be involved in cuticular lipid transportation and have adverse effects on the development and reproduction of P. citri, providing insight into the discovery of new targets for pest management based on the insect cuticle's penetration barrier function.

Transcriptome analysis unveils the mechanisms of lipid metabolism response to grayanotoxin I stress in Spodoptera litura

Background

Spodoptera litura (tobacco caterpillar, S. litura) is a pest of great economic importance due to being a polyphagous and world-distributed agricultural pest. However, agricultural practices involving chemical pesticides have caused resistance, resurgence, and residue problems, highlighting the need for new, environmentally friendly methods to control the spread of S. litura.

Aim

This study aimed to investigate the gut poisoning of grayanotoxin I, an active compound found in Pieris japonica, on S. litura, and to explore the underlying mechanisms of these effects.

Methods

S. litura was cultivated in a laboratory setting, and their survival rate, growth and development, and pupation time were recorded after grayanotoxin I treatment. RNA-Seq was utilized to screen for differentially expressed genes (DEGs). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were conducted to determine the functions of these DEGs. ELISA was employed to analyze the levels of lipase, 3-hydroxyacyl-CoA dehydrogenase (HOAD), and acetyl-CoA carboxylase (ACC). Hematoxylin and Eosin (H & E) staining was used to detect the development of the fat body.

Results

Grayanotoxin I treatment significantly suppressed the survival rate, growth and development, and pupation of S. litura. RNA-Seq analysis revealed 285 DEGs after grayanotoxin I exposure, with over 16 genes related to lipid metabolism. These 285 DEGs were enriched in the categories of cuticle development, larvae longevity, fat digestion and absorption. Grayanotoxin I treatment also inhibited the levels of FFA, lipase, and HOAD in the hemolymph of S. litura.

Conclusion

The results of this study demonstrated that grayanotoxin I inhibited the growth and development of S. litura. The mechanisms might, at least partly, be related to the interference of lipid synthesis, lipolysis, and fat body development. These findings provide valuable insights into a new, environmentally-friendly plant-derived insecticide, grayanotoxin I, to control the spread of S. litura.

Lipophorin receptor is required for the accumulations of cuticular hydrocarbons and ovarian neutral lipids in Locusta migratoria

Lipophorin is the most abundant lipoprotein particle in insect hemolymph. Lipophorin receptor (LPR) is a glycoprotein that binds to the lipophorin and mediates cellular uptake and metabolism of lipids by endocytosis. However, the roles of LPR in uptake of lipids in the integument and ovary remain unknown in the migratory locust (Locusta migratoria). In present study, we characterized the molecular properties and biological roles of LmLPR in L. migratoria. The LmLPR transcript level was high in the first 2 days of the adults after eclosion, then gradually declined. LmLPR was predominately expressed in fat body, ovary and integument. Using immuno-detection methods, we revealed that LmLPR was mainly localized in the membrane of oenocytes, epidermal cells, fat body cells and follicular cells. RNAi-mediated silencing of LmLPR led to a slight decrease of the cuticle hydrocarbon contents but with little effect on the cuticular permeability. However, the neutral lipid content was significantly decreased in the ovary after RNAi against LmLPR, which led to a retarded ovarian development. Taken together, our results indicated that LmLPR is involved in the uptake and accumulation of lipids in the ovary and plays a crucial role in ovarian development in L. migratoria. Therefore, LmLPR could be a promising RNAi target for insect pest management by disrupting insect ovarian development.

Elongases of Long-Chain Fatty Acids ELO2 and ELO9 Are Involved in Cuticle Formation and Function in Fecundity in the Yellow Fever Mosquito, Aedes aegypti

Long-chain fatty acid elongases (ELOs) play important roles in the metabolism of fatty acids in insects. In this study, the genes for two elongases from Aedes aegypti were identified, AeELO2 and AeELO9. Quantitative real time PCR showed that AeELO2 and AeELO9 are expressed at all developmental stages and some body parts, but with different expression patterns. RNAi-mediated knockdown of AeELO2 and AeELO9 was performed to investigate their roles in the development, growth, osmotic balance, and cold tolerance of Ae. aegypti. Knockdown of AeELO2 slowed larval growth and development by causing molting abnormalities. Additionally, 33% ± 3.3% of adults died during oviposition, accompanied by an abnormal extension of cuticles in AeELO2-dsRNA knockdown mosquitos. Knockdown of AeEL09 resulted in abnormal balance of cuticular osmotic pressure and a reduction in egg production. The maximal mRNAs of AeELO2 and AeELO9 were detected in eggs at 72 h after oviposition. Moreover, AeELO2 knockdown reduced the egg hatching rates and AeELO9 knockdown larvae did not develop well. In summary, AeELO2 is involved in larval molting and growth, and its knockdown affects the flexibility and elasticity of adult mosquito cuticles. AeELO9 regulates cold tolerance, osmotic balance, and egg development in Ae. aegypti.

Downregulation of NADPH-cytochrome P450 reductase via RNA interference increases the susceptibility of Acyrthosiphon pisum to desiccation and insecticides

Nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductase (CPR) is involved in the metabolism of endogenous and exogenous substances, and detoxification of insecticides. RNA interference (RNAi) of CPR in certain insects causes developmental defects and enhanced susceptibility to insecticides. However, the CPR of Acyrthosiphon pisum has not been characterized, and its function is still not understood. In this study, we investigated the biochemical functions of A. pisum CPR (ApCPR). ApCPR was found to be transcribed in all developmental stages and was abundant in the embryo stage, and in the gut, head, and abdominal cuticle. After optimizing the dose and silencing duration of RNAi for downregulating ApCPR, we found that ApCPR suppression resulted in a significant decrease in the production of cuticular and internal hydrocarbon contents, and of cuticular waxy coatings. Deficiency in cuticular hydrocarbons (CHCs) decreased the survival rate of A. pisum under desiccation stress and increased its susceptibility to contact insecticides. Moreover, desiccation stress induced a significant increase in ApCPR mRNA levels. We further confirmed that ApCPR participates in CHC production. These results indicate that ApCPR modulates CHC production, desiccation tolerance, and insecticide susceptibility in A. pisum, and presents a novel target for pest control.

Two putative fatty acid synthetic genes of BgFas3 and BgElo1 are responsible for respiratory waterproofing in Blattella germanica

Water retention is critical for physiological homeostasis and survival in terrestrial insects. While deposition of hydrocarbons on insect cuticles as a key measure for water conservation has been extensively investigated, we know little about other mechanisms for preventing water loss in insects. Here, we report two fatty acid synthetic genes that are independent of hydrocarbon production but crucial for water retention in the German cockroach Blattella germanica (L.). First, an integument enriched fatty acid elongase gene (BgElo1) was identified as a critical gene for desiccation resistance in B. germanica; however, knockdown of BgElo1 surprisingly failed to cause a decline in cuticular lipids. In addition, RNA interference (RNAi)-knockdown of an upstream fatty acid synthase gene (BgFas3) showed a similar phenotype, and transmission electron microscopy analysis revealed that BgFas3- or BgElo1-RNAi did not affect cuticle architecture. Bodyweight loss test showed that repression of BgFas3 and BgElo1 significantly increased the weight loss rate, but the difference disappeared when the respiration was closed by freeze killing the cockroaches. A water immersion test was performed, and we found that BgFas3- and BgElo1-RNAi made it difficult for cockroaches to recover from drowning, which was supported by the upregulation of hypoxia-related genes after a 10-h recovery from drowning. Moreover, a dyeing assay with water-soluble Eosin Y showed that this was caused by the entry of water into the respiratory system. Our research suggests that BgFas3 and BgElo1 are required for both inward and outward waterproofing of the respiratory system. This study benefits the understanding of water retention mechanisms in insects.

Modulation of fatty acid elongation in cockroaches sustains sexually dimorphic hydrocarbons and female attractiveness

Insect cuticular hydrocarbons (CHCs) serve as important intersexual signaling chemicals and generally show variation between the sexes, but little is known about the generation of sexually dimorphic hydrocarbons (SDHCs) in insects. In this study, we report the molecular mechanism and biological significance that underlie the generation of SDHC in the German cockroach Blattella germanica. Sexually mature females possess more C29 CHCs, especially the contact sex pheromone precursor 3,11-DimeC29. RNA interference (RNAi) screen against the fatty acid elongase family members combined with heterologous expression of the genes in yeast revealed that both BgElo12 and BgElo24 were involved in hydrocarbon (HC) production, but BgElo24 is of wide catalytic activities and is able to provide substrates for BgElo12, and only the female-enriched BgElo12 is responsible for sustaining female-specific HC profile. Repressing BgElo12 masculinized the female CHC profile, decreased contact sex pheromone level, and consequently reduced the sexual attractiveness of female cockroaches. Moreover, the asymmetric expression of BgElo12 between the sexes is modulated by sex differentiation cascade. Specifically, male-specific BgDsx represses the transcription of BgElo12 in males, while BgTra is able to remove this effect in females. Our study reveals a novel molecular mechanism responsible for the formation of SDHCs and also provide evidences on shaping of the SDHCs by sexual selection, as females use them to generate high levels of contact sex pheromone.

Sexual dimorphism of body waxes is prevalent in insects; this study reveals that the sex-differentiation pathway regulates fatty acid elongation, ensuring production of the sexually dimorphic cuticular hydrocarbons needed for high levels of sex pheromone and sexual attractiveness in female cockroaches.

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

Cytochrome P450 monooxygenases (CYPs) serve many functions in insects, from the regulation of development to xenobiotic detoxification. Several conserved CYPs have been shown to play a role in insect growth and development. CYP303A1 is a highly conserved CYP with a single ortholog in most insects, but its underlying molecular characteristics and specific physiological functions remain poorly understood. In Drosophila melanogaster and Locusta migratoria, CYP303A1 is indispensable for eclosion to adult. Here, we report additional functions of the locust gene LmCYP303A1 in nymphal molts, cuticular lipid deposition and insecticide penetration. RT-qPCR revealed that LmCYP303A1 had a high expression level before ecdysis and was highly expressed in integument, wing pads, foregut and hindgut. Suppression of LmCYP303A1 expression by RNA interference (RNAi) caused a lethal phenotype with molting defect from nymph to nymph. In addition, LmCYP303A1 RNAi resulted in locusts being more susceptible to desiccation and to insecticide toxicity. Furthermore, knockdown of LmCYP303A1 efficiently suppressed the transcript level of key genes (ELO7, FAR15 and CYP4G102) responsible for cuticular hydrocarbon (CHC) synthesis, which led to a decrease in some CHC levels. Taken together, our results suggest that one of the functions of LmCYP303A1 is to regulate the biosynthesis of CHC, which plays critical roles in protecting locusts from water loss and insecticide penetration.