FAR gene enables the brown planthopper to walk and jump on water in paddy field

Silencing fatty acyl-CoA reductase with dsRNA damaged the lipid-based cuticle barrier in Locusta migratoria

Cuticular hydrocarbons (CHCs) prevent massive water loss and are therefore essential for insect survival in scorching and dry environments. Locusta migratoria, a widespread agricultural pest, is exposed to elevated temperatures in its natural habitat. To understand the molecular mechanisms in L. migratoria against desiccation, we identified and characterized a fatty acyl-CoA reductase gene (LmFAR). LmFAR was highly expressed in the integument and fat body. Moreover, we found that LmFAR protein was localized in oenocytes. After suppressing LmFAR, over 90 % locusts died with a reduction of body water content. The procuticle structure of dsLmFAR treated insects was loose and cuticle barrier was disrupted, suggesting that FAR products are important to incorporate into the chitin matrix. dsLmFAR treated locusts showed increased sensitivity to desiccation conditions, xenobiotics and insecticides penetration was facilitated. CHC quantification by GC-MS analysis and in situ lipid detection by Bodipy both indicated that knockdown of LmFAR resulted in a decrease in total cuticle lipid amounts. In conclusion, LmFAR contributes to normal CHC amounts and cuticle integrity in locusts, thereby contributing to their adaptation to water variation.

The insecticidal toxicity of thymol and carvacrol to brown planthopper and the novel control strategy based on their disruption of the cuticular hydrophobicity

The brown planthopper (Nilaparvata lugens (Stål)) is a major pest in rice cultivation. Due to its rapid reproduction and quick resistance development, current control strategies rely heavily on chemical insecticides. This has led to resistance in brown planthoppers to various commonly used insecticides. The limitations of traditional chemical control methods highlight the urgent need for environmentally friendly and sustainable alternatives. This study evaluated the contact toxicity, fumigant toxicity, and spray treatment effects of thymol, carvacrol, and five other volatile compounds against N. lugens nymphs. Results showed that thymol and carvacrol exhibited the strongest insecticidal effects. Both the two compounds, derived from plant essential oils, are low in toxicity and significantly disrupted the hydrophobicity of the nymphs' cuticles, converting them from hydrophobic to hydrophilic. Spray experiments further confirmed their insecticidal efficacy, and rinsing N. lugens after spray treatment with both compounds significantly increased N. lugens mortality rate. GC-MS analysis revealed interactions between carvacrol and cuticular hydrophobic compounds, such as octyl palmitate. These findings suggest that thymol and carvacrol could serve as effective green bioinsecticides by targeting the cuticle and internal compounds of N. lugens. In this study, a novel pest control strategy for rice field pests such as N. lugens was proposed, aiming to disrupt their cuticular hydrophobicity, thereby preventing them from escaping when falling into water and leading to drown in the field water. This method holds promise for significantly reducing the dependence on toxic pesticides and lowering pesticide usage.

Surface hydrophobicity mechanism of poultry red mite, Dermanyssus gallinae (Acari: Dermanyssidae), gives novel meaning to chemical control

Surface hydrophobicity of organisms provides biological self-protection. The hydrophobicity of pest surface, acting as a main obstacle for the pest control, can lead to low utilization and high loss of pesticides. Dermanyssus gallinae is a notorious pest in egg-laying hens, whose control primarily depends on acaricide spraying, while its surface hydrophobicity and potential influence on pesticide effectiveness are not clear. In the present study, the contact angle measurements revealed that the surface of D. gallinae was hydrophobic. Analysis using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the surface microstructures of D. gallinae consist of cuticular folds, with a lipid-rich outermost layer of the cuticle. Based on gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC), it was found that the major compositions of cuticular lipids were fatty acids and n-alkanes. Modifying the chemical compositions and microstructures of the D. gallinae surface resulted in a reduction in surface hydrophobicity and an increase in the permeation of Rhodamine B through the cuticle. This observation suggested that the chemical compositions and microstructures were pivotal in determining surface hydrophobicity, hindering compound penetration into the cuticle. Finally, it was found improving the wettability of pesticide solution by adding surfactants could overcome the surface hydrophobicity and enhance the efficacy of pesticide against the mites. This study sheds light on the surface hydrophobicity mechanism of D. gallinae and provides a novel strategy to improve the efficacy of acaricides against the mites.

Genetic Underpinnings of Cuticular Hydrocarbon Biosynthesis in the German Cockroach, Blattella germanica (L.): Progress and Perspectives

Insect cuticular hydrocarbons (CHCs) serve as important waterproofing barriers and as signals and cues in chemical communication. Over the past 30 years, numerous studies on CHCs have been conducted in the German cockroach, Blattella germanica, leading to substantial progress in the field. However, there has not been a systematic review of CHC studies in this species in recent years. This review aims to provide a concise overview of the chemical composition, storage, transport, and physical properties of different CHCs in B. germanica. Additionally, we focus on the biosynthetic pathway and the genetic regulation of HC biosynthesis in this species. A considerable amount of biochemical evidence regarding the biosynthetic pathway of insect CHCs has been gathered from studies conducted in B. germanica. In recent years, there has also been an improved understanding of the molecular mechanisms that underlie CHC production in this insect. In this article, we summarize the biosynthesis of different classes of CHCs in B. germanica. Then, we review CHCs reaction to various environmental conditions and stressors and internal physiological states. Additionally, we review a body of work showing that in B. germanica, CHC profiles exhibit significant sexual dimorphism, specific CHCs act as essential precursors for female contact sex pheromone components, and we summarize the molecular regulatory mechanisms that underlie sexual dimorphism of CHC profiles. Finally, we highlight future directions and challenges in research on the biosynthesis and regulatory mechanisms of CHCs in B. germanica, and also identify potential applications of CHC studies in the pest control.

Silencing NlFAR7 destroyed the pore canals and related structures of the brown planthopper

Fatty acyl-CoA reductase (FAR) is one of the key enzymes, which catalyses the conversion of fatty acyl-CoA to the corresponding alcohols. Among the FAR family members in the brown planthopper (Nilaparvata lugens), NlFAR7 plays a pivotal role in both the synthesis of cuticular hydrocarbons and the waterproofing of the cuticle. However, the precise mechanism by which NlFAR7 influences the formation of the cuticle structure in N. lugens remains unclear. Therefore, this paper aims to investigate the impact of NlFAR7 through RNA interference, transmission electron microscope, focused ion beam scanning electron microscopy (FIB-SEM) and lipidomics analysis. FIB-SEM is employed to reconstruct the three-dimensional (3D) architecture of the pore canals and related cuticle structures in N. lugens subjected to dsNlFAR7 and dsGFP treatments, enabling a comprehensive assessment of changes in the cuticle structures. The results reveal a reduction in the thickness of the cuticle and disruptions in the spiral structure of pore canals, accompanied by widened base and middle diameters. Furthermore, the lipidomics comparison analysis between dsNlFAR7- and dsGFP-treated N. lugens demonstrated that there were 25 metabolites involved in cuticular lipid layer synthesis, including 7 triacylglycerols (TGs), 5 phosphatidylcholines (PCs), 3 phosphatidylethanolamines (PEs) and 2 diacylglycerols (DGs) decreased, and 4 triacylglycerols (TGs) and 4 PEs increased. In conclusion, silencing NlFAR7 disrupts the synthesis of overall lipids and destroys the cuticular pore canals and related structures, thereby disrupting the secretion of cuticular lipids, thus affecting the cuticular waterproofing of N. lugens. These findings give significant attention with reference to further biochemical researches on the substrate specificity of FAR protein, and the molecular regulation mechanisms during N. lugens life cycle.

Physiological Measurements and Transcriptomics Reveal the Fitness Costs of Monochamus saltuarius to Bursaphelenchus xylophilus

The pine wood nematode (PWN) uses several Monochamus species as vehicles, through a temporary hitchhiking process known as phoresy, enabling it to access new host plant resources. Monochamus saltuarius acts as a new and major vector of the PWN in Northeastern China, showing lower PWN carrying capacity and a shorter transmission cycle compared to established vectors. The apparently altered symbiotic relationship offers an interesting area for researching the costs and adaptions involved in nematode-beetle, a specialized phoresy. We analyzed the response and fitness costs of M. saltuarius through physiological measurements and transcriptomics. The PWN exerted adverse repercussions on the growth and development of M. saltuarius. The PWN accelerated larval development into pupae, while beetle adults carrying the PWN exhibited an elevated abnormality rate and mortality, and reduced starvation resistance. During the pupal stage, the expression of growth-related genes, including ecdysone-inducible genes (E74EA), cuticle proteins, and chitin genes (CHTs), markedly increased. Meanwhile, the induced immune response, mainly by the IMD and Toll signaling pathways, could be a contributing factor to adult abnormality and mortality. Adult gonads and trachea exhibited enrichment in pathways related to fatty acid elongation, biosynthesis, and metabolism. FASN, ELOVL, and SCD possibly contributed to resistance against PWN. Our research indicated that phoretic interactions between vector beetles and PWN vary throughout the vector's lifespan, particularly before and after entry into the trachea. This study highlighted the fitness costs of immunity and metabolism on the vector beetle, indicating the adaptation mechanisms and evolutionary trade-offs to PWN.

Acetyl coenzyme A carboxylase modulates lipogenesis and sugar homeostasis in Blattella germanica

Lipid and sugar homeostasis is critical for insect development and survival. In this study, we characterized an acetyl coenzyme A carboxylase gene in Blattella germanica (BgACC) that is involved in both lipogenesis and sugar homeostasis. We found that BgACC was dominantly expressed in the fat body and integument, and was significantly upregulated after molting. Knockdown of BgACC in 5th-instar nymphs did not affect their normal molting to the next nymphal stage, but it caused a lethal phenotype during adult emergence. BgACC-RNA interference (RNAi) significantly downregulated total free fatty acid (FFA) and triacylglycerol (TAG) levels, and also caused a significant decrease of cuticular hydrocarbons (CHCs). Repression of BgACC in adult females affected the development of oocytes and resulted in sterile females, but BgACC-RNAi did not affect the reproductive ability of males. Interestingly, knockdown of BgACC also changed the expression of insulin-like peptide genes (BgILPs), which mimicked a physiological state of high sugar uptake. In addition, BgACC was upregulated when B. germanica were fed on a high sucrose diet, and repression of BgACC upregulated the expression of the glycogen synthase gene (BgGlyS). Moreover, BgACC-RNAi increased the circulating sugar levels and glycogen storage, and a longevity assay suggested that BgACC was important for the survival of B. germanica under conditions of high sucrose uptake. Our results confirm that BgACC is involved in multiple lipid biogenesis and sugar homeostasis processes, which further modulates insect reproduction and sugar tolerance. This study benefits our understanding of the crosstalk between lipid and sugar metabolism.

Functional characterization of tyrosine melanin genes in the white-backed planthopper and utilization of a spray-based nanoparticle-wrapped dsRNA technique for pest control

As a significant pest of rice the white-backed planthopper (WBPH) Sogatella furcifera is a focus of pest management. However, traditional chemical-based control methods risk the development of pesticide resistance as well as severe ecological repercussions. Although nanoparticle-encapsulated dsRNAs provide a promising alternative method for sustainable pest management, gene targets specific to WBPH have yet to be optimized. Genes in the tyrosine-melanin pathway impact epidermal melanization and sclerotization, two processes essential for insect development and metabolism, have been proposed as good candidate targets for pest management. Seven genes (aaNAT, black, DDC, ebony, tan, TH, and yellow-y) in this group were identified from WBPH genome and functionally characterized by using RNAi for their impact on WBPH body color, development, and mortality. Knockdown of SfDDC, Sfblack, SfaaNAT, and Sftan caused cuticles to turn black, whereas Sfyellow-y and Sfebony knockdown resulted in yellow coloration. SfTH knockdown resulted in pale-colored bodies and high mortality. Additionally, an Escherichia coli expression system for large-scale dsRNA production was coupled with star polycation nanoparticles to develop a sprayable RNAi method targeting SfTH that induced high WBPH mortality rates on rice seedlings. These findings lay the groundwork for the development of large-scale dsRNA nanoparticle sprays as a WBPH control method.

Functional characterization of developmentally critical genes in the white-backed planthopper: Efficacy of nanoparticle-based dsRNA sprays for pest control

BACKGROUND

Epidermal growth factor receptor (EGFR), zinc finger homeodomain-2 (zfh-2), Abdominal-A (Abd-A), and Abdominal-B (Abd-B) regulate the growth and development of the insect abdomen. However, their potential roles in pest control have not been fully assessed. The development of insecticide resistance to multiple chemistries in the white-backed planthopper (WBPH), a major pest of rice, has prompted interest in novel pest control approaches that are ecologically friendly. Although pest management approaches based on double-stranded RNA (dsRNA)-mediated RNA interference (RNAi) have potential, their susceptibility to degradation limits large-scale field applications. These limitations, however, can be overcome with nanoparticle-dsRNA complexes that have greater environmental stability and improved cellular uptake.

RESULTS

In this study, at 5 days post-injection, transcripts for the four gene targets were reduced relative to controls and all of the experimental groups exhibited significant phenotypic defects and increased mortality. To evaluate the potential of these gene targets for field applications, a nanocarrier-dsRNA spray delivery system was assessed for RNAi efficacy. At 11 days post-spray, significant phenotypic defects and increased mortality were observed in all experimental groups.

CONCLUSION

Taken together, the results confirm the suitability of the target genes (SfEGFR, Sfzfh-2, SfAbd-A, and SfAbd-B) for pest management and demonstrate the efficacy of the nanocarrier spray system for inducing RNAi-mediated knockdown. As such, the study lays the foundation for the further development and optimization of this technology for large-scale field applications. © 2022 Society of Chemical Industry.

Genome-wide identification of FAR gene family and functional analysis of NlFAR10 during embryogenesis in the brown planthopper Nilaparvata lugens

Fatty acyl-CoA reductases (FARs) catalyze the synthesis of fatty alcohols from corresponding fatty acid precursors in organisms. However, the function of FARs in insect fecundity and embryogenesis remains largely unclear. Here, a total of 22 putative FAR proteins were identified in the brown planthopper Nilaparvata lugens, a hemipteran insect pest of rice, and most of them were highly expressed in embryonic stages. Among them, NlFAR10 was specifically and highly expressed in the later embryogenesis, but was promiscuously expressed in tissues of adults. The heterologously expressed NlFAR10 was able to produce the intermediate fatty acid alcohols from the corresponding acyl-CoA precursors. When NlFAR10 was silenced through RNAi in vivo, the embryogenesis was obviously inhibited, resulting in low hatching rates. Moreover, the metabolome analyses indicated that loss of NlFAR10 affected lipid metabolism and purine metabolism during embryogenesis. To the best of our knowledge, this is the first report of a FAR member affecting insect embryogenesis, thus providing a new target for future pest management.

FAR knockout significantly inhibits Chilo suppressalis survival and transgene expression of double-stranded FAR in rice exhibits strong pest resistance

Chilo suppressalis is one of the most prevalent and damaging rice pests, causing significant economic losses each year. Chemical control is currently the primary method of controlling C. suppressalis. However, the indiscriminate use of chemical insecticides increases pest resistance, pollutes the environment and poses a significant health threat to humans and livestock, highlighting the need to find safer, more pest-specific and more effective alternatives to pest control. Plant-mediated RNA interference (RNAi) is a promising agricultural pest control method that is highly pest-specific and has less of an impact on the environment. Using multi-sgRNAs/Cas9 technology to delete Fatty acyl-CoA reductase (FAR) of C. suppressalis in the G0 generation, we show that downregulating FAR transcription may significantly increase the mortality rate and darken the epidermis of C. suppressalis compared with the control. Subsequently, we developed dsFAR transgenic rice lines using Agrobacterium-mediated genetic transformation and then screened three strains expressing dsFAR at high levels using transcriptional level analysis. Using transgenic rice stems, a laboratory feeding bioassay indicated that at least one line (L#10) displayed a particularly high level of insect resistance, with an insect mortality rate of more than 80%. In the field trials, dsFAR transgenic rice displayed high levels of resistance to C. suppressalis damage. Collectively, these results suggest the potential of a new environment-friendly, species-specific strategy for rice pest management.

Fatty acyl-CoA reductase influences wax biosynthesis in the cotton mealybug, Phenacoccus solenopsis Tinsley

Mealybugs are highly aggressive to a diversity of plants. The waxy layer covering the outermost part of the integument is an important protective defense of these pests. However, the molecular mechanisms underlying wax biosynthesis in mealybugs remain largely unknown. Here, we analyzed multi-omics data on wax biosynthesis by the cotton mealybug, Phenacoccus solenopsis Tinsley, and found that a fatty acyl-CoA reductase (PsFAR) gene, which was highly expressed in the fat bodies of female mealybugs, contributed to wax biosynthesis by regulating the production of the dominant chemical components of wax, cuticular hydrocarbons (CHCs). RNA interference (RNAi) against PsFAR by dsRNA microinjection and allowing mealybugs to feed on transgenic tobacco expressing target dsRNA resulted in a reduction of CHC contents in the waxy layer, and an increase in mealybug mortality under desiccation and deltamethrin treatments. In conclusion, PsFAR plays crucial roles in the wax biosynthesis of mealybugs, thereby contributing to their adaptation to water loss and insecticide stress.

The role of a fatty acyl-CoA reductase (PsFAR) in wax biosynthesis of cotton mealybug is investigated, RNAi against PsFAR resulted in insects with lower generation of waxy filaments and higher mortality under desiccation and deltamethrin treatments.

Chitin synthase 1 and five cuticle protein genes are involved in serosal cuticle formation during early embryogenesis to enhance eggshells in Nilaparvata lugens

Many holo- and hemimetabolous insects enhance their eggshells during embryogenesis by forming a serosal cuticle (SC). To date, scholarly understanding of the SC composition and SC-related gene functions has been limited, especially for hemimetabolous insects. In this study, we initially performed transmission electron microscopic (TEM) observation and chitin staining of the SC in Nilaparvata lugens, a hemimetabolous rice pest known as the brown planthopper (BPH). We confirmed that the SC was a chitin-rich lamellar structure deposited gradually during the early embryogenesis. Parental RNA interference (RNAi) against Nilaparvata lugens chitin synthase 1 (NlCHS1) in newly emerged and matured females resulted in decreases of egg hatchability by 100% and 76%, respectively. Ultrastructural analyses revealed loss of the lamellar structure of the SC in dsNlCHS1-treated eggs. According to temporal expression profiles, five cuticle protein coding genes, NlugCpr1/2/3/8/90, were specifically or highly expressed during the SC formation period, and NlugCpr1/2/3/90 were further detected in 72 h eggshells extract by ultra-performance liquid chromatography-tandem mass spectrometry/mass spectrometry. NlugCpr2/3/90 were likely three SC-specific cuticle proteins. TEM observations of the SC following parental RNAi against NlugCpr1/2/3/8/90 demonstrated that NlugCpr3/8/90 were essential for SC formation. The study provided an understanding of the SC formation process and SC-related cuticle proteins in BPHs, which offer potential targets for pest control in the egg stage as well.

A CYP380C10 gene is required for waterproofing and water retention in the insect integument

Cuticular hydrocarbons (CHCs) are important components in the integument of insects and are required for development and survival. Insect-specific CYP4G subfamily, of the P450 enzymes, catalyze the oxidative decarbonylation step in the biosynthesis of CHCs. Here, we characterized CYP380C10 gene function in a Hemiptera rice pest, Nilaparvata lugens. We used RNA interference-mediated expression silencing to reveal that NlCYP380C10 played a key role in waterproofing and water-retention in the integument of N. lugens. Knockdown of NlCYP380C10 significantly reduced body weight and caused mortality. Scanning electron microscopy showed the loss of the lipid layer on the surface of the abdominal cuticle of the dsNlCYP380C10-injected adults. Furthermore, CHC profile analysis revealed that NlCYP380C10 knockdown significantly decreased the amounts of CHCs in adult females. This suggested that NlCYP380C10 was involved in CHC biosynthesis. Reduction of CHC content caused the loss of the intact lipid layer of the cuticle, which resulted in loss of the waterproofing and water-retention functions. This led to failure of molting and eclosion. Our findings expanded the knowledge of CHC biosynthesis in the insect integument and led to a better understanding of the functional roles of CYP450 genes involved in waterproofing and water-retention in insects.

CPR Gene Contributes to Integument Function and Ovary Development in a Rice Planthopper

Nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductase (CPR) is an essential enzyme that transfers electrons from NADPH to cytochrome P450 monooxygenases. CPR is involved in cuticular hydrocarbon (CHC) synthesis in insects and is vital for insect development and survival. Here, we clarify the physiological function of a CPR gene in Nilaparvata lugens, an important rice pest, by using RNA interference. CPR gene knockdown leads to the functional loss of waterproofing and water retention in the integument of female adults, which causes significantly reduced body weight and a lethal phenotype. Scanning electron microscopy shows that the lipid layer on the outermost surface of the abdominal cuticle becomes thin in dsCPR-injected adults. Furthermore, CHC profile analysis reveals that CPR knockdown significantly decreases the contents of CHCs with a carbon chain length ≥ C27 in adult females. Moreover, we find that CPR knockdown generates a deficient phenotype in ovaries with deformed oocytes and a complete failure of egg-laying. These findings suggest that CPR plays multiple functional roles in CHC biosynthesis and embryo development in insects.

Rice functional genomics: decades' efforts and roads ahead

Rice (Oryza sativa L.) is one of the most important crops in the world. Since the completion of rice reference genome sequences, tremendous progress has been achieved in understanding the molecular mechanisms on various rice traits and dissecting the underlying regulatory networks. In this review, we summarize the research progress of rice biology over past decades, including omics, genome-wide association study, phytohormone action, nutrient use, biotic and abiotic responses, photoperiodic flowering, and reproductive development (fertility and sterility). For the roads ahead, cutting-edge technologies such as new genomics methods, high-throughput phenotyping platforms, precise genome-editing tools, environmental microbiome optimization, and synthetic methods will further extend our understanding of unsolved molecular biology questions in rice, and facilitate integrations of the knowledge for agricultural applications.

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.

Cuticular Hydrocarbon Plasticity in Three Rice Planthopper Species

Insect cuticular hydrocarbons (CHCs) are organic compounds of the surface lipid layer, which function as a barrier against water loss and xenobiotic penetration, while also serving as chemical signals. Plasticity of CHC profiles can vary depending upon numerous biological and environmental factors. Here, we investigated potential sources of variation in CHC profiles of Nilaparvata lugens, Laodelphax striatellus and Sogatella furcifera, which are considered to be the most important rice pests in Asia. CHC profiles were quantified by GC/MS, and factors associated with variations were explored by conducting principal component analysis (PCA). Transcriptomes were further compared under different environmental conditions. The results demonstrated that CHC profiles differ among three species and change with different developmental stages, sexes, temperature, humidity and host plants. Genes involved in cuticular lipid biosynthesis pathways are modulated, which might explain why CHC profiles vary among species under different environments. Our study illustrates some biological and ecological variations in modifying CHC profiles, and the underlying molecular regulation mechanisms of the planthoppers in coping with changes of environmental conditions, which is of great importance for identifying potential vulnerabilities relating to pest ecology and developing novel pest management strategies.

Advances in deciphering the genetic basis of insect cuticular hydrocarbon biosynthesis and variation

Cuticular hydrocarbons (CHCs) have two fundamental functions in insects. They protect terrestrial insects against desiccation and serve as signaling molecules in a wide variety of chemical communication systems. It has been hypothesized that these pivotal dual traits for adaptation to both desiccation and signaling have contributed to the considerable evolutionary success of insects. CHCs have been extensively studied concerning their variation, behavioral impact, physiological properties, and chemical compositions. However, our understanding of the genetic underpinnings of CHC biosynthesis has remained limited and mostly biased towards one particular model organism (Drosophila). This rather narrow focus has hampered the establishment of a comprehensive view of CHC genetics across wider phylogenetic boundaries. This review attempts to integrate new insights and recent knowledge gained in the genetics of CHC biosynthesis, which is just beginning to incorporate work on more insect taxa beyond Drosophila. It is intended to provide a stepping stone towards a wider and more general understanding of the genetic mechanisms that gave rise to the astonishing diversity of CHC compounds across different insect taxa. Further research in this field is encouraged to aim at better discriminating conserved versus taxon-specific genetic elements underlying CHC variation. This will be instrumental in greatly expanding our knowledge of the origins and variation of genes governing the biosynthesis of these crucial phenotypic traits that have greatly impacted insect behavior, physiology, and evolution.

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.

Ten fatty acyl-CoA reductase family genes were essential for the survival of the destructive rice pest, Nilaparvata lugens

BACKGROUND

Fatty alcohols are the precursors of sex pheromone components, wax esters and hydrocarbons in insects. Fatty acyl-CoA reductases (FARs) are important enzymes required for the reduction of fatty alcohol and thereby contribute to the production of cuticular hydrocarbon (CHC).

RESULTS

Based on bioinformatics analyses we identified 17 FAR genes in the brown planthopper, Nilaparvata lugens. RNA interference against these genes demonstrated that ten NlFAR genes were essential for the survival of N. lugens. For instance, knockdown of NlFAR5, 6, 11 or 15 was lethal and caused a slender body shape, while the old cuticles of the respective animals remained attached to the abdomen or failed to split open from the nota. Knockdown of NlFAR9 resulted in a phenotype, with a smooth body surface and a decrease in CHC amounts. Similarly, CHC deficiency in N. lugens resulted in increased adhesion of water droplets and secreted honeydew to the insect surface and the inability of N. lugens to survive in paddy fields with varying humidity. Knockdown of NlFAR1, 4, 5, 6, 8, 9, 11 and 13 additionally resulted in female adult infertility.

CONCLUSION

The present study illustrates the structural and functional differences of FAR family genes and provides potential targets for RNA interference-based rice planthopper management. © 2020 Society of Chemical Industry.

FoxO directly regulates the expression of TOR/S6K and vitellogenin to modulate the fecundity of the brown planthopper

As a conserved transcription factor, FoxO plays a crucial role in multiple physiological processes in vivo, including stress resistance, longevity, growth and reproduction. Previous studies on FoxO have focused on human, mouse, Drosophila melanogaster and Caenorhabditis elegans, while there are few reports on agricultural pests and little is known about how FoxO modulates insect fecundity. In Asia, the brown planthopper (BPH) Nilaparvata lugens (Stål) is one of the most serious pests in rice production and high fecundity is the basis of the outbreak of BPH. Here, using the genome-wide ChIP-seq of NlFoxO in BPH, we found that NlFoxO binds to the promoters of ribosomal proteinS6 kinase (NlS6K) and serine/threonine-protein kinase mTOR (NlTOR) and increases their expression levels. We also found that NlFoxO directly binds to the exon of vitellogenin (NlVg) and has a specific inhibitory effect on its expression. In addition, the number of eggs laid and their hatching rate decreased significantly after injection of NlFoxO double-stranded RNA into BPH adults. Our findings provide direct evidence that FoxO modulates insect fecundity through binding to the promoters of NlS6K, NlTOR and the exon of NlVg and affecting their gene expression in the Vg network.

The fatty acid elongase gene family in the brown planthopper, Nilaparvata lugens

The cuticular hydrocarbon (CHC) biosynthetic pathways branches off from the synthesis of fatty acids. Fatty acid elongases (ELOs) are enzymes catalyzing the synthesis of long-chain fatty acids and thereby contribute to the diversification of CHCs. Based on bioinformatics analyses we identified 20 ELO genes in the brown planthopper, Nilaparvata lugens. RNA interference against these genes demonstrated that 9 NlELO genes were essential for the survival of N. lugens nymphs and adults. Indeed, knockdown of NlELOs 1, 3, 4, 7, 8, 9, 10, 12 and 18 caused lethal phenotypes with a thin and wizened body and reduced lipids in the fat body. Surface analysis by scanning electron microscopy and CHC quantification indicated that knockdown of NlELOs 2, 3, 8 and 16 additionally resulted in a smooth body surface and a decrease in CHC amounts. Therefore, we speculate that long-chain CHCs are needed for CHC attachment to the cuticle surface. CHC deficiency, in turn, resulted in increased adhesion of water droplets and secreted honeydew to the animal surface and the inability of N. lugens to survive in paddy fields with varying humidity. Our present study provides an initial comprehensive analysis of ELO gene functions in an insect, and may serve to better understand the biology of CHCs.