Conserved microRNAs miR-8-5p and miR-2a-3p modulate chitin biosynthesis in response to 20-hydroxyecdysone signaling in the brown planthopper, Nilaparvata lugens

MicroRNA novel-miR-90-5p modulates larval molt development in Ostrinia furnacalis (Guenée) by targeting OfCYP18A1

The hormone 20-hydroxyecdysone (20E) plays an important role in the physiological processes of insect growth, development, and ecdysis, whereas CYP18A1, a 20E hydroxylase, participates in 20E degradation and maintains its equilibrium state, which is an indispensable part of the 20E signaling pathway. MicroRNAs (miRNAs) are important post-transcriptional regulators of gene expression and mediate various biological processes. However, whether and how miRNAs regulate CYP18A1 remains unclear. Herein, OfCYP18A1 was expressed in different developmental stages and tissues. After OfCYP18A1 knockdown, the survival and ecdysis rates of larvae as well as their body weight and length significantly decreased, causing the larvae to molt early but not completely, resulting in death. The concentration of 20E in larvae significantly increased, whereas that of juvenile hormone (JH) significantly decreased. To further investigate the regulatory mechanism of OfCYP18A1, an miRNA (novel-miR-90-5p) targeting OfCYP18A1 was proposed. Novel-miR-90-5p was expressed in different developmental stages and tissues of Ostrinia furnacalis, and it exhibited an inverse trend to OfCYP18A1. Novel-miR-90-5p overexpression in O. furnacalis significantly decreased larval survival and ecdysis rates, delayed their development, decreased the larval body size, increased 20E concentration, and decreased JH concentration. However, after novel-miR-90-5p expression inhibition, the survival rate of 3rd-instar larvae did not significantly differ, their body weight and length significantly increased, ecdysis was delayed, 20E concentration significantly decreased, and JH concentration did not significantly change. These findings reveal that miRNAs are involved in OfCYP18A1 regulation during insect growth and development, thus enhancing our understanding of insect defense strategies.

Insecticide-induced sublethal effect in the fall armyworm is mediated by miR-9993/miR-2a-3p - FPPS/JHAMT - JH molecular module

The sublethal effect of insecticides can affect the population dynamics of pests by changing the physiological or behavioral changes, which poses a serious threat to the sustainable control of crop pests in the field. However, the molecular regulation mechanism that mediates the sublethal effect of insecticides on crop pests remains unsolved. Here, we show that the sublethal effect of spinetoram and cyantraniliprole on Spodoptera frugiperda is mediated by the molecular module of microRNA-9993/microRNA-2a-3p - farnesyl diphosphate synthase gene (FPPS)/juvenile hormone (JH) acid methyltransferase gene (JHAMT) - JH. Spinetoram prolonged the duration of larvae and pupae, decreased the weight of pupae, while cyantraniliprole prolonged the duration of larvae and decreased the emergence rate. Similarly, injection of the juvenile hormone analogue (JHA) methoprene significantly prolonged the developmental duration of larvae and pupae, decreased the pupal weight and emergence rate. This sublethal phenotypic change was due to the upregulation of key JH synthesis genes, including FPPS and JHAMT, mediated by spinetoram and cyantraniliprole, resulting in an increase in JH titer. Furthermore, it was confirmed by small RNA sequencing, dual luciferase analysis and agomir-miRNA injection, miR-9993 and miR-2a-3p that it could bind FPPS and JHAMT respectively, and regulated the expression level of FPPS and JHAMT to affect the titer of JH, thus changing the phenotype of S. frugiperda. Collectively, these results provide insights into the mechanism of insecticide regulation of sublethal effects of pests, expand our understanding of development-related miRNAs, and reveal key factors involved in JH signaling pathways that support sublethal effects of insecticides.

Identification of miR-71* as a regulator of Flotillin-1 in egg development of Rhipicephalus sanguineus

Identifying the microRNAs (miRNAs) that regulate the growth and development of Rhipicephalus sanguineus (Rh. sanguineus) is essential for developing effective control strategies against both the tick and tick-borne pathogens. This study reveals the antagonistic regulatory mechanism between miR-71* (the passenger strand of miRNA-71) and Flotillin-1 in the egg development of Rh. sanguineus. Through bioinformatics prediction and validation using a dual-luciferase reporter system, we demonstrate for the first time that miR-71* directly targets and regulates Flotillin-1. Functional experiments indicate that inhibiting miR-71* significantly increases tick egg weight, while suppressing Flotillin-1 reduces egg weight, thereby suggesting that these molecules negatively regulate egg developmental processes. This discovery provides a novel target for elucidating reproductive regulatory pathways in ticks and lays a theoretical foundation for developing control strategies against ticks and tick-borne pathogens.

Transcriptomic Characterization of miRNAs in Pyrrhalta aenescens Fairmaire in Response to 20-Hydroxyecdysone Treatment

BACKGROUND/OBJECTIVES

Pyrrhalta aenescens, a major pest of elm trees, causes extensive ecological and economic damage through rapid population growth and defoliation. Existing research mainly focuses on its biological traits and chemical control, with little knowledge about its reproductive development mechanisms, a key factor in population expansion. In other insects, the steroid hormone 20-hydroxyecdysone (20E) regulates development and reproduction via microRNA (miRNA)-mediated pathways, but this has not been studied in P. aenescens. This study aimed to systematically identify miRNAs responsive to 20E in P. aenescens and unravel their roles in regulating reproduction and metabolic pathways, providing foundational insights into hormone-miRNA crosstalk in this ecologically significant pest.

METHODS

Adult beetles (collected from Baotou, Inner Mongolia) were injected with 1.0 μg/μL 20E or control. Total RNA from three biological replicates (10 adults each) was sequenced, followed by miRNA identification, differential expression analysis, target prediction, and functional enrichment.

RESULTS

Small RNA sequencing identified 205 miRNAs (162 conserved, 43 novel), with 12 DEMs post-20E treatment. Target prediction linked these miRNAs to 7270 genes, including key regulators of the FoxO signaling pathway and MAPK signaling pathway. KEGG analysis highlighted lipid metabolism and stress response pathways.

CONCLUSIONS

This study revealed that 20E modulates miRNA networks to regulate FoxO and MAPK pathways in P. aenescens, suggesting hormonal control of lipid metabolism and developmental processes. As the first miRNA resource for this pest, our findings provide mechanistic insights into 20E-miRNA crosstalk and identify potential molecular targets for disrupting its reproductive biology, laying a foundation for eco-friendly pest control.

Insect metamorphosis and chitin metabolism under miRNA regulation: a review with current advances

Insect metamorphosis is a complex developmental process regulated by microRNAs (miRNAs) and hormonal signaling pathways. Key genes driving insect ontogenic changes are precisely modulated by miRNAs, which interact with 20-hydroxyecdysone (20E) and juvenile hormone (JH) to coordinate developmental transitions. Over the past decade, significant progress has been made in understanding miRNA biogenesis, their regulatory roles in gene expression, and their involvement in critical biological processes, including metamorphosis and chitin metabolism. miRNAs are now recognized as essential regulators of chitin metabolism and hormonal signaling, ensuring precise control of insect development. Disrupting the expression of participating genes in hormone signaling pathways through miRNAs leads to aberrant metamorphosis and consequent lethal outcomes, highlighting their potential as targets for pest control. This review summarizes current advances in miRNA-mediated regulation of insect metamorphosis and chitin metabolism, with a focus on their interactions with 20E and JH signaling pathways. By integrating recent findings, we provide insights into the molecular mechanisms underlying miRNA function in developmental transitions and their potential applications in insect pest management strategies. © 2025 Society of Chemical Industry.

miR-34-5p, a potential RNA biopesticide for controlling Spodoptera frugiperda by targeting of SfEcR and SfE74

Spodoptera frugiperda is an agricultural pest with strong adaptability and migration ability. For decades, chemical control has been an important technical measure for controlling S. frugiperda. In the field of pest control, research on RNA biopesticides mainly focuses on dsRNA, and the application of miRNA biopesticides is still in its infancy. The miR-34 family is a multifunctional family that plays key roles in organ development, organism or organ aging, stress response, spermatogenesis, and signal transduction. In this study, we analyzed the physiological function of miR-34-5p by upregulating and downregulating its level, combined with a series of methods such as target site prediction, dual luciferase reporter gene detection, related gene expression, and intestinal reactive oxygen species (ROS) level detection. miR-34-5p plays a crucial role in the metamorphosis and development of S. frugiperda larvae. Among them, the molting related genes SfEcR and SfE74 were identified as the target genes for miR-34-5p, which suggests that miR-34-5p has the potential to serve as an RNA biopesticide. This work provides novel directions and ideas for the prevention and green control of S. frugiperda.

Cuticle thickening mediates insecticide penetration resistance in Spodoptera litura

INTRODUCTION

Long-term and extensive use of chemical pesticides has led to the development of resistance in many important agricultural pests. The mechanisms of resistance formation in pests are complex and variable, and unraveling the resistance mechanisms is the key to control resistant pests. Insect cuticle, as the first line of defense for insecticides, plays a non-negligible role in insecticide penetration resistance. Although penetration resistance is widespread in insects, the multiple molecular mechanisms that impede insecticide penetration are unclear, especially in Spodoptera litura.

OBJECTIVES

This study aims to reveal the molecular mechanisms of insecticide penetration resistance in S. litura.

METHODS

The structure and thickness of cuticle were analyzed by TEM, and the role of cuticle in penetration resistance was determined by different application methods. The molecular mechanism of cuticular proteins overexpression was analyzed using RNAi, TEM, dual-luciferase assay and EMSA from cis- and trans-acting factors. In addition, the relationship between the chitin synthetic pathway and insecticide resistance was explored through enzyme activity, inhibitor assay, molecular docking and RNAi. Furthermore, the role of 20E in penetration resistance was analyzed.

RESULTS

The cuticle of the resistant populations was significantly thickened and accompanied by extrusion, which contributed significantly to indoxacarb resistance. Constitutive upregulation of trans-acting factor SlituFTZ-F1 co-regulates the overexpression of SlituCP26 with cis-acting elements in the SlituCP26 promoter (74 bp insertion), affecting the cuticle thickness‑mediated indoxacarb penetration resistance. Meanwhile, the overexpression of key genes in the chitin synthesis pathway increased the chitin content, which combined with SlituCP26 to participate in indoxacarb resistance. Moreover, 20E affected the SlituFTZ-F1-mediated regulatory pathway and chitin biosynthesis pathway in indoxacarb resistance.

CONCLUSION

This study comprehensively elucidated the molecular mechanism of cuticle thickening mediating penetration resistance to indoxacarb and confirmed its existence in the field populations of S. litura.

Developmental Expression Patterns of miRNA in Mythimna separata Walker (Lepidotera: Noctuidae)

BACKGROUND/OBJECTIVES

miRNAs are a family of single-stranded non-coding RNAs that regulate gene expression by targeting messenger RNAs (mRNAs) for suppression, with an average length of 22 nt. The oriental armyworm, Mythimna separata Walker, is a pest insect with long-distance migratory capability, which causes severe loss of grains and pastures in Eastern Asia, Southeastern Asia, and Oceania. This study aims to elucidate the post-transcriptional regulatory mechanisms of miRNAs in the development of this pest.

METHODS

We carried out small RNA sequencing on samples from eggs, third instar larvae, pre-pupae, pupae, and adults.

RESULTS

A total of 400 miRNAs were identified, among which 40 were known and 360 were novel miRNAs. Dynamic trend analysis of miRNAs revealed that 199 miRNAs were highly expressed in eggs (profile 12), while 173 miRNAs were highly expressed in both eggs and pupae (profile 13). The results of differential expression analysis of miRNAs (DEmiR) revealed that 75 miRNAs were significantly more abundant in eggs compared to other developmental stages. Furthermore, more up-regulated miRNAs were observed than down-regulated miRNAs in adults relative to 3rd instar larvae, pre-pupae, and pupae. The core genes for miRNA biosynthesis-Pasha, Dicer1, and Ago1-were highly expressed in eggs but poorly expressed in 3rd instar larvae. KEGG enrichment analyses indicated that several genes in the pentose and glucuronate interconversion pathway, as well as the fructose and mannose metabolism pathway, were regulated by DEmiRs.

CONCLUSIONS

DEmiRNAs targeted most genes of M. separata, resulting in a complex miRNA-mRNA regulation mode.

The miR-31b targets arylsulfatase B to regulate the ovarian development of Bactrocera dorsalis

BACKGROUND

Reproduction is the basis of insect population growth and evolution, and encompasses ovarian development, reproductive behavior, and fecundity. Bactrocera dorsalis is a globally significant agricultural pest that is subject to quarantine, with mated females that can lay over 3000 eggs. The post-transcriptional regulation of ovarian development remains unclear. Here, miR-31b is shown to be involved in regulating Bactrocera dorsalis ovarian development.

RESULTS

CRISPR/Cas9 was used to generate miR-31b loss-of-function mutations in Bactrocera dorsalis. The removal of miR-31b resulted in severely impaired ovarian development in adults, with phenotypes that included dramatically reduced egg production and hatching rates. The relationship between miR-31b and its target gene arylsulfatase B (ARSB) was subsequently identified using the methods of bioinformatics, transcriptomic sequencing, quantitative polymerase chain reaction (qPCR), RNA pull-down and dual-luciferase reporter assay. Finally, miR-31b was confirmed to bind the target gene arylsulfatase B to affect metabolism and thereby further hindered ovarian development of Bactrocera dorsalis.

CONCLUSION

Overall, these results provide new insights into molecular mechanisms at the post-transcriptional level in regulating ovarian development and insect reproduction, consequently providing potential targets to control arthropod pests through the reproductive strategy. © 2024 Society of Chemical Industry.

Identification of a vital transcription factor of the alanine aminotransferase in the brown planthopper and its upstream regulatory pathways

The brown planthopper (Nilaparvata lugens) is an important insect pest of rice, and can rapidly adapt to insect-resistant rice varieties. In our previous studies, alanine aminotransferase in N. lugens (NlALT) was found to play an important role in the adaptation of the brown planthopper to resistant rice IR36. Here, we further identified CCAAT/enhancer binding protein (NlC/EBP) as a vital transcription factor of NlALT. Nlp38b in the MAPKs pathway regulated the expression of NlALT by influencing the phosphorylation level of NlC/EBP. In addition, we found that NlGRL101, a G protein-coupled receptor (GPCR), was significantly higher expressed in the N. lugens population adapted to IR36 (P-IR36). After knockdown of NlGRL101 through RNAi in P-IR36 population, lower expressions of Nlp38b and NlC/EBP, along with reduced phosphorylation levels of Nlp38b and NlC/EBP were observed; moreover, NlALT activity and honeydew amount were decreased by 15.68% and 76.08%, respectively. These results indicated that insect-resistant rice IR36 induced expression of NlGRL101, which enhanced expression of NlALT through Nlp38b and NlC/EBP. These findings are helpful for better understanding of insect adaptation to resistant crop varieties.

MicroRNA miR-285 modulates the metamorphosis in Galeruca daurica by targeting Br-C

BACKGROUND

Galeruca daurica has become a new pest on the Inner Mongolia grasslands since an abrupt outbreak in 2009 caused serious damage. As a pupa indicator during insect metamorphosis, the early response gene of the ecdysone signaling pathway, Broad-Complex (Br-C), plays a vital role in the growth and development of insects. MicroRNAs (miRNAs) are small non-coding RNAs which mediate various biological activities, but it is unknown whether and how Br-C is regulated by miRNAs.

RESULTS

Temporal expression profiles revealed that miR-285 and Br-C basically displayed an opposite trend during larval-adult development, and Br-C was sharply up-regulated on the last day of final-instar larvae while miR-285 was significantly down-regulated. Both dual-luciferase reporter assay and miRNA-mRNA interaction assay indicated that miR-285 interacts with the coding sequence of Br-C and represses its expression. Not only overexpression but also downexpression of miR-285 led to the failure of larval to pupal to adult metamorphosis. In addition, both overexpression of miR-285 and silence of Br-C inhibited the expression of Br-C and other ecdysone signaling pathway genes, including E74, E75, ECR, FTZ-F1, and HR3. On the contrary, suppressing miR-285 obtained opposite results. Further experiments showed that 20-hydroxyecdysone down-regulated miR-285 and up-regulated Br-C and above-mentioned genes, whereas juvenile hormone alalogue (JHA) resulted in opposite effects.

CONCLUSION

Our results reveal that miR-285 is involved in mediating the metamorphosis in G. daurica by targeting Br-C in the ecdysone signaling pathway. miR-285 and its target Br-C could be as a potential target for G. daurica management. © 2024 Society of Chemical Industry.

Conserved microRNAs miR-8-3p and miR-2a-3 targeting chitin biosynthesis to regulate the molting process of Sogatella furcifera (Horváth)(Hemiptera: Delphacidae)

Molting is a key solution to growth restriction in insects. The periodic synthesis and degradation of chitin, one of the major components of the insect epidermis, is necessary for insect growth. MicroRNA (miRNA) have been implicated in molting regulation, yet their involvement in the interplay interaction between the chitin synthesis pathway and 20-hydroxyecdysone signaling remains poorly understood. In this study, soluble trehalase (Tre1) and phosphoacetylglucosamine mutase (PAGM) were identified as targets of conserved miR-8-3p and miR-2a-3, respectively. The expression profiles of miR-8-3p-SfTre1 and miR-2a-3-SfPAGM exhibited an opposite pattern during the different developmental stages, indicating a negative regulatory relationship between them. This relationship was confirmed by an in vitro dual-luciferase reporter system. Overexpression of miR-8-3p and miR-2a-3 by injection of mimics inhibited the expression of their respective target genes and increased mortality, leading to death in the pre-molting, and molting death phenomena. They also caused a decrease in chitin content and expression levels of key genes in the chitin synthesis pathway (SfTre1, SfTre2, SfHK, SfG6PI, SfGFAT, SfGNA, SfPAGM, SfUAP, SfCHS1, SfCHS1a, and SfCHS1b). Conversely, the injection of miRNA inhibitors resulted in the upregulation of the expression levels of these genes. Following 20E treatment, the expression levels of miR-8-3p and miR-2a-3 decreased significantly, while their corresponding target genes increased significantly. These results indicate that miR-8-3p and miR-2a-3 play a regulatory role in the molting of Sogatella furcifera by targeting SfTre1 and SfPAGM, respectively. These findings provide new potential targets for the development of subsequent new control strategies.

Insecticide resistance reduces the profitability of insect-resistant rice cultivars

INTRODUCTION

Preventing crop yield loss caused by pests is critical for global agricultural production. Agricultural pest control has largely relied on chemical pesticides. The interaction between insecticide resistance and the adaptation of herbivorous pests to host plants may represent an emerging threat to future food security.

OBJECTIVES

This study aims to unveil genetic evidence for the reduction in the profitability of resistant cultivars derived from insecticide resistance in target pest insects.

METHODS

An experimental evolution system encompassing resistant rice and its major monophagous pest, the brown planthopper Nilaparvata lugens, was constructed. Whole genome resequencing and selective sweep analysis were utilized to identify the candidate gene loci related to the adaptation. RNA interference and induced expression assay were conducted to validate the function of the candidate loci.

RESULTS

We found that the imidacloprid-resistant population of N. lugens rapidly adapted to resistant rice IR36. Gene loci related to imidacloprid resistance may contribute to this phenomenon. Multiple alleles in the nicotinic acetylcholine receptor (nAChR)-7-like and P450 CYP4C61 were significantly correlated with changes in virulence to IR36 rice and insecticide resistance of N. lugens. One avirulent/susceptible genotype and two virulent/resistant genotypes could be inferred from the corresponding alleles. Importantly, we found that the virulent/resistant genotypes already exist in the wild in China, exhibiting increasing frequencies along with insecticide usage. We validated the relevance of these genotypes and the virulence to three more resistant rice cultivars. Knockdown of the above two genes in N. lugens significantly decreased both the resistance to imidacloprid and the virulence towards resistant rice.

CONCLUSION

Our findings provide direct genetic evidence to the eco-evolutionary consequence of insecticide resistance, and suggest an urgent need for the implementation of predictably sustainable pest management.

MicroRNA miR-7-5p targets MARK2 to control metamorphosis in Galeruca daurica

The MARK2 gene, coding microtubule affinity-regulating kinase or serine/threonine protein kinase, is an important modulator in organism microtubule generation and cell polarity. However, its role in the metamorphosis of insects remains unknown. In this study, we found a conserved miRNA, miR-7-5p, which targets MARK2 to participate in the regulation of the larval-pupal metamorphosis in Galeruca daurica. The dual luciferase reporter assay showed that miR-7-5p interacted with the 3' UTR of MARK2 and repressed its expression. The expression profiling of miR-7-5p and MARK2 displayed an opposite trend during the larval-adult development process. In in-vivo experiments, overexpression of miR-7-5p by injecting miR-7-5p agomir in the final instar larvae down-regulated MARK2 and up-regulated main ecdysone signaling pathway genes including E74, E75, ECR, FTZ-F1 and HR3, which was similar to the results from knockdown of MARK2 by RNAi. In contrast, repression of miR-7-5p by injecting miR-7-5p antagomir obtained opposite effects. Notably, both overexpression and repression of miR-7-5p in the final instar larvae caused abnormal molting and high mortality during the larval-pupal transition, and high mortality during the pupal-adult transition. The 20-hydroxyecdysone (20E) injection experiment showed that 20E up-regulated miR-7-5p whereas down-regulated MARK2. This study reveals that the accurate regulation of miRNAs and their target genes is indispensable for insect metamorphosis.

Untangling the gordian knot: The intertwining interactions between developmental hormone signaling and epigenetic mechanisms in insects

Hormones control developmental and physiological processes, often by regulating the expression of multiple genes simultaneously or sequentially. Crosstalk between hormones and epigenetics is pivotal to dynamically coordinate this process. Hormonal signals can guide the addition and removal of epigenetic marks, steering gene expression. Conversely, DNA methylation, histone modifications and non-coding RNAs can modulate regional chromatin structure and accessibility and regulate the expression of numerous (hormone-related) genes. Here, we provide a review of the interplay between the classical insect hormones, ecdysteroids and juvenile hormones, and epigenetics. We summarize the mode-of-action and roles of these hormones in post-embryonic development, and provide a general overview of epigenetic mechanisms. We then highlight recent advances on the interactions between these hormonal pathways and epigenetics, and their involvement in development. Furthermore, we give an overview of several 'omics techniques employed in the field. Finally, we discuss which questions remain unanswered and possible avenues for future research.

A time course analysis through diapause reveals dynamic temporal patterns of microRNAs associated with endocrine regulation in the butterfly Pieris napi

Organisms inhabiting highly seasonal environments must cope with a wide range of environmentally induced challenges. Many seasonal challenges require extensive physiological modification to survive. In winter, to survive extreme cold and limited resources, insects commonly enter diapause, which is an endogenously derived dormant state associated with minimized cellular processes and low energetic expenditure. Due to the high degree of complexity involved in diapause, substantial cellular regulation is required, of which our understanding primarily derives from the transcriptome via messenger RNA expression dynamics. Here we aim to advance our understanding of diapause by investigating microRNA (miRNA) expression in diapausing and direct developing pupae of the butterfly Pieris napi. We identified coordinated patterns of miRNA expression throughout diapause in both head and abdomen tissues of pupae, and via miRNA target identification, found several expression patterns to be enriched for relevant diapause-related physiological processes. We also identified two candidate miRNAs, miR-14-5p and miR-2a-3p, that are likely involved in diapause progression through their activity in the ecdysone pathway, a critical regulator of diapause termination. miR-14-5p targets phantom, a gene in the ecdysone synthesis pathway, and is upregulated early in diapause. miR-2a-3p has been found to be expressed in response to ecdysone, and is upregulated during diapause termination. Together, the expression patterns of these two miRNAs match our current understanding of the timing of hormonal regulation of diapause in P. napi and provide interesting candidates to further explore the mechanistic role of microRNAs in diapause regulation.

miR-306-5p is involved in chitin metabolism in Aedes albopictus pupae via linc8338-miR-306-5p-XM_019678125.2 axis

Aedes albopictus can transmit several lethal arboviruses. This mosquito has become a sever public health threat due to its rapidly changing global distribution. Chitin, which is the major component of the cuticle and peritrophic membrane (PM), is crucial for the growth and development of insect. microRNAs (miRNAs) play important roles in the posttranscriptional level regulation of gene expression, thereby influencing many biological processes in insects. In this study, an attempt was made to evaluate the role of miR-306-5p in regulating chitin metabolism in Ae. albopictus pupae. Overexpression of miR-306-5p resulted in a significantly reduced survival rate in pupae and an increased malformation rate in adults. Both in vivo and in vitro evidence confirmed the presence of the competing endogenous RNA (ceRNA) regulatory axis (linc8338-miR-306-5p-XM_019678125.2). RNAi of linc8338 and XM_019678125.2 had effects on pupae similar to those of miR-306-5p. The highest expression level of miR-306-5p was found in the midgut, and alteration in the expression of miR-306-5p, XM_019678125.2 and linc8338 induced increased transcript levels of chitin synthase 2 (AaCHS2) and decreased chitinase 10 (AaCht10); as well as increased thickness of the midgut and enlarged midgut epithelial cells. The results of this study highlight the potential of miR-306-5p as a prospective target in mosquito control and confirm that the ceRNA mechanism is involved in chitin metabolism. These findings will provide a basis for further studies to uncover the molecular mechanisms through which ncRNAs regulate chitin metabolism.

The roles of small RNAs in rice-brown planthopper interactions

Interactions between rice plants (Oryza sativa L.) and brown planthoppers (Nilaparvata lugens Stål, BPHs) are used as a model system to study the molecular mechanisms underlying plant-insect interactions. Small RNAs (sRNAs) regulate growth, development, immunity, and environmental responses in eukaryotic organisms, including plants and insects. Recent research suggests that sRNAs play significant roles in rice-BPH interactions by mediating post-transcriptional gene silencing. The focus of this review is to explore the roles of sRNAs in rice-BPH interactions and to highlight recent research progress in unraveling the mechanism of cross-kingdom RNA interference (ckRNAi) between host plants and insects and the application of ckRNAi in pest management of crops including rice. The research summarized here will aid in the development of safe and effective BPH control strategies.

MicroRNA-989 controls Aedes albopictus pupal-adult transition process by influencing cuticle chitin metabolism in pupae

BACKGROUND

Aedes albopictus is a vector of numerous devastating arboviruses and places heavy burdens on global public health. Chitin is one of the important components of cuticles and targeting chitin metabolism is a promising strategy for preventing mosquito dispersal and mosquito-borne diseases. Increasing evidence suggests that microRNAs (miRNAs) play crucial roles in various physiological processes of insects.

METHODS

A previous analysis suggested that the microRNA miR-989 is potentially involved in chitin metabolism in Ae. albopictus pupae. In the present study, we found that the expression level of miR-989 was significantly overexpressed after injection of agomir. A dual-luciferase assay was used to determine the direct target of miR-989. Survival rate, eclosion rate and malformation rate were statistically analyzed to evaluate the potential effect of miR-989. Hematoxylin-eosin staining and chitin staining were used to evaluate the microstructural changes in the cuticles of Ae. albopictus pupae.

RESULTS

Overexpression of miR-989 resulted in a significantly reduced survival rate and eclosion rate of pupae and an elevated malformation rate of adults. The results suggested that miR-989 acted as a regulator of chitin metabolism in Ae. albopictus pupae by affecting the transcript levels of the Ae. albopictus genes encoding chitin synthase 1 (AaCHS1) and chitinase 10 (AaCht10). The altered expression levels of the two chitin metabolism-related enzymes (CHS1 and Cht10, respectively) caused the structural changes in cuticles and further affected the pupal-adult transition process of Ae. albopictus. XM_029863591.1 was proven to be the target gene of miR-989 and displayed similar effects on pupae as miR-989.

CONCLUSIONS

The microRNA miR-989 was found to be essential for chitin metabolism in old and new cuticles of Ae. albopictus pupae. The results of the current study suggested that miR-989 could be used as a potential target to control Ae. albopictus.

Insights into the microRNA landscape of Rhodnius prolixus, a vector of Chagas disease

The growing interest in microRNAs (miRNAs) over recent years has led to their characterization in numerous organisms. However, there is currently a lack of data available on miRNAs from triatomine bugs (Reduviidae: Triatominae), which are the vectors of the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. A comprehensive understanding of the molecular biology of vectors provides new insights into insect-host interactions and insect control approaches, which are key methods to prevent disease incidence in endemic areas. In this work, we describe the miRNome profiles from gut, hemolymph, and salivary gland tissues of the Rhodnius prolixus triatomine. Small RNA sequencing data revealed abundant expression of miRNAs, along with tRNA- and rRNA-derived fragments. Fifty-two mature miRNAs, previously reported in Ecdysozoa, were identified, including 39 ubiquitously expressed in the three tissues. Additionally, 112, 73, and 78 novel miRNAs were predicted in the gut, hemolymph, and salivary glands, respectively. In silico prediction showed that the top eight most highly expressed miRNAs from salivary glands potentially target human blood-expressed genes, suggesting that R. prolixus may modulate the host's gene expression at the bite site. This study provides the first characterization of miRNAs in a Triatominae species, shedding light on the role of these crucial regulatory molecules.

CRISPR/Cas9-mediated genome editing of gustatory receptor NlugGr23a causes male sterility in the brown planthopper Nilaparvata lugens

Gustatory receptors (Grs) have an essential role in chemical recognition so as to evaluate food quality. Insect Grs also participate in non-gustatory functions, such as olfaction, temperature sensing, and mating. In this study, we knocked out NlugGr23a, a putative fecundity-related Gr, using the CRISPR/Cas9 system in the brown planthopper Nilaparvata lugens, a serious insect pest of rice. Surprisingly, homozygous NlugGr23a mutant (NlugGr23a^-/-) males were sterile but their sperm were motile and morphologically normal. DAPI staining of mutant sperm inseminated eggs showed that most of NlugGr23a^-/- sperm failed to fertilize eggs, even if they were capable of entering into the egg as a result of their arrested development prior to male pronucleus formation. Immunohistochemistry demonstrated the expression of NlugGr23a in testis. Moreover, prior mating by NlugGr23a^-/- males suppressed female fertility. To our knowledge, it is the first report that a chemoreceptor is implicated in male sterility and provides a potential molecular target for genetic pest control alternatives.

Oxalic Acid Inhibits Feeding Behavior of the Brown Planthopper via Binding to Gustatory Receptor Gr23a

Plants produce diverse secondary compounds as natural protection against microbial and insect attack. Most of these compounds, including bitters and acids, are sensed by insect gustatory receptors (Grs). Although some organic acids are attractive at low or moderate levels, most acidic compounds are potentially toxic to insects and repress food consumption at high concentrations. At present, the majority of the reported sour receptors function in appetitive behaviors rather than aversive taste responses. Here, using two different heterologous expression systems, the insect Sf9 cell line and the mammalian HEK293T cell line, we started from crude extracts of rice (Oryza sativa) and successfully identified oxalic acid (OA) as a ligand of NlGr23a, a Gr in the brown planthopper Nilaparvata lugens that feeds solely on rice. The antifeedant effect of OA on the brown planthopper was dose dependent, and NlGr23a mediated the repulsive responses to OA in both rice plants and artificial diets. To our knowledge, OA is the first identified ligand of Grs starting from plant crude extracts. These findings on rice-planthopper interactions will be of broad interest for pest control in agriculture and also for better understanding of how insects select host plants.

Genome-wide identification of lncRNAs associated with viral infection in Spodoptera frugiperda

The role of lncRNAs in immune defence has been demonstrated in many multicellular and unicellular organisms. However, investigation of the identification and characterization of long non-coding RNAs (lncRNAs) involved in the insect immune response is still limited. In this study, we used RNA sequencing (RNA-seq) to investigate the expression profiles of lncRNAs and mRNAs in the fall armyworm Spodoptera frugiperda in response to virus infection. To assess the tissue- and virus-specificity of lncRNAs, we analysed and compared their expression profiles in haemocytes and fat body of larvae infected with two entomopathogenic viruses with different lifestyles, i.e. the polydnavirus HdIV (Hyposoter didymator IchnoVirus) and the densovirus JcDV (Junonia coenia densovirus). We identified 1883 candidate lncRNAs, of which 529 showed differential expression following viral infection. Expression profiles differed considerably between samples, indicating that many differentially expressed (DE) lncRNAs showed virus- and tissue-specific expression patterns. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment and target prediction analyses indicated that DE-LncRNAs were mainly enriched in metabolic process, DNA replication and repair, immune response, metabolism of insect hormone and cell adhesion. In addition, we identified three DE-lncRNAs potentially acting as microRNA host genes, suggesting that they participate in gene regulation by producing miRNAs in response to virus infection. This study provides a catalogue of lncRNAs expressed in two important immune tissues and potential insight into their roles in the antiviral defence in S. frugiperda. The results may help future in-depth functional studies to better understand the biological function of lncRNAs in interaction between viruses and the fall armyworm.

Identification and profiling of Sogatella furcifera microRNAs and their potential roles in regulating the developmental transitions of nymph-adult

Sogatella furcifera is one of the most serious insect pests that affect rice in Asia. One class of small RNAs (sRNAs; ~22 nt long) is miRNAs, which participate in various biological processes by regulating the expression of target genes in a spatiotemporal manner. However, the role of miRNAs in nymph-to-adult transition in S. furcifera remains unknown. In this study, we sequenced sRNA libraries of S. furcifera prepared from individuals at three different developmental stages (pre-moult, moulting and early adult). A total of 253 miRNAs (134 known and 119 novel) were identified, of which 12 were differentially expressed during the nymph-to-adult developmental transition. Moreover, Real time quantitative PCR (RT-qPCR) analysis revealed that all 12 miRNAs were differentially expressed among five different nymph tissues and 14 different developmental stages (first to fifth instar nymphs and 1-day-old adults). Injection of miR-2a-2 mimic/antagomir and miR-305-5p-1 mimic/antagomir into 1-day-old fifth instar nymphs significantly increased the mortality rate. In addition, a defective moulting phenotype was observed in nymphs injected with miR-2a-2 and miR-305-5p-1, suggesting that these miRNAs are involved in S. furcifera nymph-adult transition. In conclusion, these results reveal the function of critical miRNAs in S. furcifera nymph-adult transition, and also provide novel potential targets of insecticides for the long-term sustainable management of S. furcifera.

Population density modulates insect progenitive plasticity through the regulation of dopamine biosynthesis

Insect fecundity is a quantitative phenotype strongly affected by genotypes and the environment. However, interactions between genotypes and environmental factors in modulating insect fecundity remain largely unknown. This study investigated the impact of population density on the fecundity of Nilaparvata lugens (brown planthopper; BPH) carrying homozygous high- (HFG) or low- (LFG) fecundity homozygous genotypes. Under low population densities, the fecundity and population growth rate of both genotypes showed similar increasing trends across generations, while the trends between HFG and LFG under high population densities were opposite. Through a combination of temporal analysis and weighted gene co-expression network analyses on RNA-seq data of HFG and LFG under low and high population densities in the 1st, 3rd, and 5th generations, we identified 2 gene modules that were associated with these density-dependent progenitive phenotypes. Four pathways related to the neural system were simultaneously enriched by the 2 gene modules. Furthermore, Nlpale, which encodes a tyrosine hydroxylase, was identified as a key gene. The RNA interference of this gene and manipulation of its downstream product dopamine significantly affected the basic and density-dependent progenitive phenotypes of BPH. These findings indicated that dopamine biosynthesis is the key regulatory factor that determines fecundity in response to density changes in different BPH genotypes. Thus, this study provides insights into the interaction of a typical environmental factor and insect genotype during the process of population regulation.

Versatile Roles of Microbes and Small RNAs in Rice and Planthopper Interactions

Planthopper infestation in rice causes direct and indirect damage through feeding and viral transmission. Host microbes and small RNAs (sRNAs) play essential roles in regulating biological processes, such as metabolism, development, immunity, and stress responses in eukaryotic organisms, including plants and insects. Recently, advanced metagenomic approaches have facilitated investigations on microbial diversity and its function in insects and plants, highlighting the significance of microbiota in sustaining host life and regulating their interactions with the environment. Recent research has also suggested significant roles for sRNA-regulated genes during rice-planthopper interactions. The response and behavior of the rice plant to planthopper feeding are determined by changes in the host transcriptome, which might be regulated by sRNAs. In addition, the roles of microbial symbionts and sRNAs in the host response to viral infection are complex and involve defense-related changes in the host transcriptomic profile. This review reviews the structure and potential functions of microbes and sRNAs in rice and the associated planthopper species. In addition, the involvement of the microbiota and sRNAs in the rice-planthopper-virus interactions during planthopper infestation and viral infection are discussed.

miR-309a is a regulator of ovarian development in the oriental fruit fly Bactrocera dorsalis

Fecundity is arguably one of the most important life history traits, as it is closely tied to fitness. Most arthropods are recognized for their extreme reproductive capacity. For example, a single female of the oriental fruit fly Bactrocera dorsalis, a highly invasive species that is one of the most destructive agricultural pests worldwide, can lay more than 3000 eggs during its life span. The ovary is crucial for insect reproduction and its development requires further investigation at the molecular level. We report here that miR-309a is a regulator of ovarian development in B. dorsalis. Our bioinformatics and molecular studies have revealed that miR-309a binds the transcription factor pannier (GATA-binding factor A/pnr), and this activates yolk vitellogenin 2 (Vg 2) and vitellogenin receptor (VgR) advancing ovarian development. We further show that miR-309a is under the control of juvenile hormone (JH) and independent from 20-hydroxyecdysone. Thus, we identified a JH-controlled miR-309a/pnr axis that regulates Vg2 and VgR to control the ovarian development. This study has further enhanced our understanding of molecular mechanisms governing ovarian development and insect reproduction. It provides a background for identifying targets for controlling important Dipteran pests.

The ovary is a very critical organ for insect reproduction. Especially, many insect pests are famous for their large reproductive capacity. Therefore, understanding the molecular mechanisms involved in ovarian development could significantly contribute in the development of new insect pest control strategies. In this study, we report that miR-309a regulates the development of the ovary in an important dipteran pest, B. dorsalis, through a transcriptional factor, pannier (GATA-binding factor A/pnr), which in turn directly mediates the expression of yolk vitellogenin 2 (Vg 2) and vitellogenin receptor (VgR). Moreover, miR-309a is under the upstream control of juvenile hormone (JH). Here, in Dipterans, a novel JH-miR-309a-pnr-Vg-related genes regulatory pathway was found in ovarian development. This finding advances our understanding of a mechanism regulating insect ovarian development and provides new insights for potential targets to control dipteran pests through the reproductive strategy.

Transcriptome and metabolome analyses reveal the responses of brown planthoppers to RH resistant rice cultivar

The brown planthopper (BPH) Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) is one of the most destructive rice pests in Asia. The application of insect-resistant rice cultivars is currently one of the principal means of controlling BPH. Understanding the physiological response mechanisms of BPH feeding on insect-resistant rice is the key for maintaining rice yield. Here, we measured the ecological fitness and analyzed the whole-body transcriptome and metabolome of BPH reared on susceptible cultivar Taichung Native 1 (TN1) and resistant cultivar Rathu Heenati (RH). Our results showed that RH significantly decreased the survival rate, female adult weight, honeydew secretion, the number of eggs laid per female and fat content of BPH. We identified 333 upregulated and 486 downregulated genes in BPH feeding on RH. These genes were mainly involved in energy metabolism, amino acid metabolism, hormone synthesis and vitamin metabolism pathways. We also detected 145 differentially accumulated metabolites in BPH reared on RH plants compared to BPH reared on TN1 plants, including multiple carbohydrates, amino acids, lipids, and some nucleosides. Combined analyses of transcriptome and metabolome showed that five pathways, including starch, sucrose, and galactose metabolism, were altered. The network for these pathways was subsequently visualized. Our results provide insights into the mechanisms of metabolite accumulation in BPH feeding on the RH rice variety. The results could help us better understand how insect-resistant rice cultivars combat BPH infestation, which is important for the comprehensive management of BPH.

Identification and profiling of stable microRNAs in hemolymph of young and old Locusta migratoria fifth instars

Since the discovery of the first microRNA (miRNA) in the nematode Caenorhabditis elegans, numerous novel miRNAs have been identified which can regulate presumably every biological process in a wide range of metazoan species. In accordance, several insect miRNAs have been identified and functionally characterized. While regulatory RNA pathways are traditionally described at an intracellular level, studies reporting on the presence and potential role of extracellular (small) sRNAs have been emerging in the last decade, mainly in mammalian systems. Interestingly, evidence in several species indicates the functional transfer of extracellular RNAs between donor and recipient cells, illustrating RNA-based intercellular communication. In insects, however, reports on extracellular small RNAs are emerging but the number of detailed studies is still very limited. Here, we demonstrate the presence of stable sRNAs in the hemolymph of the migratory locust, Locusta migratoria. Moreover, the levels of several extracellular miRNAs (ex-miRNAs) present in locust hemolymph differed significantly between young and old fifth nymphal instars. In addition, we performed a 'proof of principle' experiment which suggested that extracellularly delivered miRNA molecules are capable of affecting the locusts' development.

LncRNA-IRAR-mediated regulation of insulin receptor transcripts in Drosophila melanogaster during nutritional stress

The insulin signalling pathway plays a crucial role in regulating the metabolism of sugars, fats and proteins in cells, thereby affecting the growth, metabolism, reproduction and ageing of organisms. However, little is known about the functions of long non-coding RNAs (lncRNAs) in the regulation of insulin receptors under stress conditions in insects. In this study, we showed that insulin receptor-associated lncRNA (IRAR) regulates insulin receptor transcripts in response to nutritional stress in Drosophila melanogaster. Genome editing by CRISPR-Cas9 showed reduced sensitivity of IRAR mutants to environmental nutritional changes. In contrast, the sensitivity of mutants overexpressing tubulin-gal4 > IRAR increased under low nutrition. The pupation and eclosion timings in IRAR mutants were significantly delayed with an increase in insulin concentration compared with that in the w1118 group. In addition, the expression pattern of IRAR was almost consistent with that of the four transcripts of the insulin receptor from the embryonic period to the adult period. RNA immunoprecipitation assay showed the direct regulation of insulin receptor transcripts by IRAR to the through FOXO binding under nutritional stress. To our knowledge, this is the first study that describes a model of lncRNA-mediated development regulation through insulin receptor transcripts.

MiR-3017b contributes to metamorphosis by targeting sarco/endoplasmic reticulum Ca2+ ATPase in Tribolium castaneum

In recent years, increasing numbers of microRNAs (miRNAs) have been reported to regulate insect metamorphosis. One thousand, one hundred fifty-four miRNAs have been previously identified from Tribolium castaneum by high-throughput sequencing; however, little is known about which miRNAs can participate in metamorphosis, leaving the role of miRNAs in regulating the underlying mechanism elusive. Here, we report the participation of miR-3017b in the metamorphosis of T. castaneum. Temporal profiles revealed that miR-3017b was highly expressed at the late larval stage, but significantly decreased at the early pupal stage. Overexpression of miR-3017b caused larval to pupal to adult metamorphosis arrested. Dual-luciferase reporter assay and miRNA-mRNA interaction assay illustrated that miR-3017b interacts with the coding sequence of sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) and suppresses its expression. Knockdown of SERCA caused metamorphosis arrested, similar to that observed in miR-3017b overexpression beetles. Further functional mechanism analyses revealed that 20-hydroxyecdysone application downregulates miR-3017b and up-regulates SERCA expression. The expression level of downstream genes in the 20E pathway was disrupted after overexpressing miR-3017 and the knockdown of SERCA. These results provided evidence miR-3017b-SERCA contributes to metamorphosis by regulating the 20E pathway in T. castaneum. It could advance our understanding of the coordination of 20E and miRNA regulation in insect metamorphosis.

Whole-transcriptome RNA sequencing revealed the roles of chitin-related genes in the eyestalk abnormality of a novel mud crab hybrid (Scylla serrata ♀ × S. paramamosain ♂)

Chitin is a kind of insoluble structural polysaccharide and plays different roles in different species. In crustaceans, it forms the structural components in the exoskeleton. In our previous studies, novel mud crab hybrids have been produced from the interspecific hybridization of Scylla serrata ♀ × S. paramamosain ♂. Some of the hybrid crabs have been found to be morphologically (eyestalk) abnormal, but the genetic mechanism remains unknown. To address this question, we performed whole-transcriptome RNA sequencing on the control group (normal hybrids), abnormal hybrids, and S. paramamosain to uncover the genetic basis underlying this morphological abnormality. A total of 695 mRNAs, 10 miRNAs, 44 circRNAs, and 1957 lncRNAs were differentially expressed between normal and abnormal hybrids. Several differentially expressed genes (DEGs) associated with chitin and cuticle metabolism were identified, including chitin synthase, chitinase, chitin deacetylase, β-N-acetylglucosaminidase, β-1,4-endoglucanase, N-alpha-acetyltransferase, cuticle proprotein, early cuticle protein, and arthrodial cuticle protein. Functional analysis showed that DE miRNAs, DE circRNAs, DE lncRNAs, and lncRNA/circRNA-miRNA-mRNA network were enriched in pathways related to the amino acid, carbohydrate, and glycogen metabolism. Considering the importance of the chitin and cuticle in exoskeleton formation, it can be concluded that the changes in the chitin and cuticle biosynthesis might have caused the eyestalk abnormality in hybrid crabs. These findings can lay the solid foundation for a better understanding of the important roles of chitin and cuticle related genes and the development of hybridization techniques in crustaceans.

miRNAs targeting CYP6ER1 and CarE1 are involved in nitenpyram resistance in Nilaparvata lugens

The evolution of nitenpyram resistance has been confirmed to be related to overexpression of two key metabolic enzyme genes, CYP6ER1 and CarE1, in Nilaparvata lugens, a highly destructive rice pest that causes substantial economic losses and has developed insecticide resistance. As microRNAs (miRNAs) are important post-transcriptional regulators of gene expression, whether they are involved in nitenpyram resistance is poorly understood in N. lugens. In this study, knockdown of key genes in the miRNA biogenesis pathway (Dicer1, Drosha, and Argonaute1) changed CYP6ER1 and CarE1 abundance, which confirmed the importance of miRNAs in nitenpyram resistance. Furthermore, global screening of miRNAs associated with nitenpyram resistance in N. lugens was performed, and a total of 42 known and 178 novel miRNAs were identified; of these, 57 were differentially expressed between the susceptible and resistant strains, and two (novel_85 and novel_191) were predicted to target CYP6ER1 and CarE1, respectively. Luciferase reporter assays demonstrated that novel_85 and novel_191 bind to the CYP6ER1 and CarE1 coding regions, respectively, and downregulate their expression. Moreover, modulating novel_85 and novel_191 expression by injection of miRNA inhibitors and mimics significantly altered N. lugens nitenpyram susceptibility. This is the first study to systematically screen and identify miRNAs associated with N. lugens nitenpyram resistance, and provides important information that can be used to develop new miRNA-based targets in insecticide resistance management.

Genome-wide Analysis of Alternative Gene Splicing Associated with Virulence in the Brown Planthopper Nilaparvata lugens (Hemiptera: Delphacidae)

Alternative splicing of protein coding genes plays a profound role in phenotypic variation for many eukaryotic organisms. The development of high-throughput sequencing and bioinformatics algorithms provides the possibility of genome-wide identification of alternative splicing events in eukaryotes. However, for the brown planthopper Nilaparvata lugens, a destructive pest of rice crops, whole-genome distribution of alternative splicing events and the role of alternative splicing in the phenotypic plasticity of virulence have not previously been estimated. Here, we developed an analysis pipeline to identify alternative splicing events in the genome of N. lugens. Differential expression analysis and functional annotation were performed on datasets related to different virulence phenotypes. In total, 27,880 alternative splicing events corresponding to 9,787 multi-exon genes were detected in N. lugens. Among them, specifically expressed alternative splicing transcripts in the virulent Mudgo population were enriched in metabolic process categories, while transcripts in the avirulent TN1 population were enriched in regulator activity categories. In addition, genes encoding odorant receptor, secreted saliva protein and xenobiotic metabolic P450 monooxygenase showed different splicing patterns between Mudgo population and TN1 population. Host change experiment also revealed that an isoform of a P450 gene could be specially induced by the stimulation of resistant rice variety Mudgo. This research pioneered a genome-wide study of alternative gene splicing in the rice brown planthopper. Differences in alternative splicing between virulent and avirulent populations indicated that alternative splicing might play an important role in the formation of virulence phenotypes in N. lugens.

Overexpression of an Osa-miR162a Derivative in Rice Confers Cross-Kingdom RNA Interference-Mediated Brown Planthopper Resistance without Perturbing Host Development

Rice is a main food crop for more than half of the global population. The brown planthopper (BPH, Nilaparvata lugens) is one of the most destructive insect pests of rice. Currently, repeated overuse of chemical insecticides represents a common practice in agriculture for BPH control, which can induce insect tolerance and provoke environmental concerns. This situation calls for innovative and widely applicable strategies for rice protection against BPH. Here we report that the rice osa-miR162a can mediate cross-kingdom RNA interference (RNAi) by targeting the NlTOR (Target of rapamycin) gene of BPH that regulates the reproduction process. Through artificial diet or injection, osa-miR162a mimics repressed the NlTOR expression and impaired the oviposition of BPH adults. Consistently, overproduced osa-miR162a in transgenic rice plants compromised the fecundity of BPH adults fed with these plants, but meanwhile perturbed root and grain development. To circumvent this issue, we generated osa-miR162a-m1, a sequence-optimized osa-miR162a, by decreasing base complementarity to rice endogenous target genes while increasing base complementarity to NlTOR. Transgenic overexpression of osa-miR162a-m1 conferred rice resistance to BPH without detectable developmental penalty. This work reveals the first cross-kingdom RNAi mechanism in rice-BPH interactions and inspires a potentially useful approach for improving rice resistance to BPH. We also introduce an effective strategy to uncouple unwanted host developmental perturbation from desirable cross-kingdom RNAi benefits for overexpressed plant miRNAs.

A novel approach to co-expression network analysis identifies modules and genes relevant for moulting and development in the Atlantic salmon louse (Lepeophtheirus salmonis)

BACKGROUND

The salmon louse (Lepeophtheirus salmonis) is an obligate ectoparasitic copepod living on Atlantic salmon and other salmonids in the marine environment. Salmon lice cause a number of environmental problems and lead to large economical losses in aquaculture every year. In order to develop novel parasite control strategies, a better understanding of the mechanisms of moulting and development of the salmon louse at the transcriptional level is required.

METHODS

Three weighted gene co-expression networks were constructed based on the pairwise correlations of salmon louse gene expression profiles at different life stages. Network-based approaches and gene annotation information were applied to identify genes that might be important for the moulting and development of the salmon louse. RNA interference was performed for validation. Regulatory impact factors were calculated for all the transcription factor genes by examining the changes in co-expression patterns between transcription factor genes and deferentially expressed genes in middle stages and moulting stages.

RESULTS

Eight gene modules were predicted as important, and 10 genes from six of the eight modules have been found to show observable phenotypes in RNA interference experiments. We knocked down five hub genes from three modules and observed phenotypic consequences in all experiments. In the infection trial, no copepodids with a RAB1A-like gene knocked down were found on fish, while control samples developed to chalimus-1 larvae. Also, a FOXO-like transcription factor obtained highest scores in the regulatory impact factor calculation.

CONCLUSIONS

We propose a gene co-expression network-based approach to identify genes playing an important role in the moulting and development of salmon louse. The RNA interference experiments confirm the effectiveness of our approach and demonstrated the indispensable role of a RAB1A-like gene in the development of the salmon louse. We propose that our approach could be generalized to identify important genes associated with a phenotype of interest in other organisms.

The microRNA miR-184 regulates the CYP303A1 transcript level to control molting of Locusta migratoria

Cytochrome P450 monooxygenases (CYPs) play essential physiological functions in insects. CYP303A1 is highly conserved in insect species studied to date, and shows an indispensable role for adult eclosion in both Locusta migratoria and Drosophila melanogaster. However, how CYP303A1 is regulated to control insect developmental processes remains uninvestigated. In this study, we discovered functional binding sites for miR-184 in the coding sequence of LmCYP303A1. The luciferase reporter assay showed that miR-184 could target LmCYP303A1 and regulate its expression in vitro. Furthermore, overexpression of miR-184 through microinjection of agomir to locusts reduced the transcripts of LmCYP303A1 and led to abnormal molting, which is similar to the phenotype of silencing LmCYP303A1 by direct injection of dsLmCYP303A1 to locusts. Meanwhile, down-regulation of miR-184 by injection of antagomir increased the LmCYP303A1 transcript and caused molting defects. These findings suggested that miR-184 could target LmCYP303A1 to regulate the molting process in L. migratoria, which might be considered as a novel target for pest control.

Genome-Wide Identification and Characterization of Amino Acid Polyamine Organocation Transporter Family Genes Reveal Their Role in Fecundity Regulation in a Brown Planthopper Species (Nilaparvata lugens)

The brown planthopper (BPH), Nilaparvata lugens Stål (Hemiptera:Delphacidae), is one of the most destructive pests of rice worldwide. As a sap-feeding insect, the BPH is incapable of synthesizing several amino acids which are essential for normal growth and development. Therefore, the insects have to acquire these amino acids from dietary sources or their endosymbionts, in which amino acid transporters (AATs) play a crucial role by enabling the movement of amino acids into and out of insect cells. In this study, a common amino acid transporter gene family of amino acid/polyamine/organocation (APC) was identified in BPHs and analyzed. Based on a homology search and conserved functional domain recognition, 20 putative APC transporters were identified in the BPH genome. Molecular trait analysis showed that the verified BPH APC family members were highly variable in protein features, conserved motif distribution patterns, and exon/intron organization. Phylogenetic analysis of five hemipteran species revealed an evolutionary pattern of interfamily conservation and lineage-specific expansion of this gene family. Moreover, stage- and tissue-specific expression analysis revealed diverse expression patterns in the 20 BPH APC transporter genes. Lastly, a potential BPH fecundity regulatory gene of NlAPC09 was identified and shown to participate in the fecundity regulation through the use of quantitative polymerase chain reaction (qPCR) and RNA inference experiments. Our results provide a basis for further functional investigations of APC transporters in BPH.

Identification of putative abdominal vibration-related genes through transcriptome analyses in the brown planthopper (Nilaparvata lugens)

The sexually mature female brown planthoppers (BPHs) send out abdominal vibration (AV) signals through the rice so that the males can obtain intraspecific, gender, and localization information to prepare for mating. Destroying vibration signals is an alternative biological method for pest control. However, the regulatory mechanism of AV in female BPHs remains elusive, which presents an obstacle to pest control. We observed that before mating female BHPs emitted abdominal vibration signals that disappeared immediately after mating and reappeared after 6 days. Therefore, ovarian and brain samples of female BPHs from Unmated-6h⁺ (with AV), Mated-6h^- (without AV) and Mated-6d⁺ (with AV) individuals were collected for transcript analyses. By transcriptional sequencing analyses, 33 candidate genes that might involve in the regulation of female AV were obtained. After selecting 4 candidate genes of them for verification by RNA interference (RNAi), it was found that interference of juvenile hormone binding protein (JHBP) could greatly reduce the probability and frequency of AV for female BPHs. In general, this study identified AV-related candidate genes in female BPHs through transcriptome analyses and provided an important basis for future research on pest control in BPHs.

Regulatory roles of microRNAs in insect pests: prospective targets for insect pest control

At the post-transcriptional level, microRNAs (miRNAs) play an important role in the regulation of gene expression, thereby influencing the outcome of many biological processes in insects, such as development, reproduction, metamorphosis, immunity, and insecticide resistance. The alteration of miRNA expression by mimic/agomir or inhibitor/antagomir via injection/feeding can lead to pest developmental abnormalities, death, or reduced pesticide resistance, indicating that miRNAs are potential targets for pest control. This review provides an overview of recent advances in understanding the regulatory roles of miRNA in agricultural and public health insect pest, and further highlights the potential of miRNAs as prospective targets in pest control.

Peroxiredoxin alleviates the fitness costs of imidacloprid resistance in an insect pest of rice

Chemical insecticides have been heavily employed as the most effective measure for control of agricultural and medical pests, but evolution of resistance by pests threatens the sustainability of this approach. Resistance-conferring mutations sometimes impose fitness costs, which may drive subsequent evolution of compensatory modifier mutations alleviating the costs of resistance. However, how modifier mutations evolve and function to overcome the fitness cost of resistance still remains unknown. Here we show that overexpression of P450s not only confers imidacloprid resistance in the brown planthopper, Nilaparvata lugens, the most voracious pest of rice, but also leads to elevated production of reactive oxygen species (ROS) through metabolism of imidacloprid and host plant compounds. The inevitable production of ROS incurs a fitness cost to the pest, which drives the increase or fixation of the compensatory modifier allele T65549 within the promoter region of N. lugens peroxiredoxin (NlPrx) in the pest populations. T65549 allele in turn upregulates the expression of NlPrx and thus increases resistant individuals' ability to clear the cost-incurring ROS of any source. The frequent involvement of P450s in insecticide resistance and their capacity to produce ROS while metabolizing their substrates suggest that peroxiredoxin or other ROS-scavenging genes may be among the common modifier genes for alleviating the fitness cost of insecticide resistance.

Comparative proteomics provides insights into diapause program of Bactrocera minax (Diptera: Tephritidae)

The Chinese citrus fly, Bactrocera minax, is a notorious univoltine pest that causes damage to citrus. B. minax enters obligatory pupal diapause in each generation to resist harsh environmental conditions in winter. Despite the enormous efforts that have been made in the past decade, the understanding of pupal diapause of B. minax is currently still fragmentary. In this study, the 20-hydroxyecdysone solution and ethanol solvent was injected into newly-formed pupae to obtain non-diapause- (ND) and diapause-destined (D) pupae, respectively, and a comparative proteomics analysis between ND and D pupae was performed 1 and 15 d after injection. A total of 3,255 proteins were identified, of which 190 and 463 were found to be differentially abundant proteins (DAPs) in ND1 vs D1 and ND15 vs D15 comparisons, respectively. The reliability and accuracy of LFQ method was validated by qRT-PCR. Functional analyses of DAPs, including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment, and protein-protein interaction (PPI) network construction, were conducted. The results revealed that the diapause program of B. minax is closely associated with several physiological activities, such as phosphorylation, chitin biosynthesis, autophagy, signaling pathways, endocytosis, skeletal muscle formation, protein metabolism, and core metabolic pathways of carbohydrate, amino acid, and lipid conversion. The findings of this study provide insights into diapause program of B. minax and lay a basis for further investigation into its underlying molecular mechanisms.

Hormonal regulation of microRNA expression dynamics in the gut of the yellow fever mosquito Aedes aegypti

The yellow fever mosquito Aedes aegypti is an obligatory blood feeder and a major arboviral disease vector, evoking severe public health concerns worldwide. In adult female mosquitoes, the gut is critical for blood digestion and pathogen entry. We aimed for a systematic exploration of microRNA expression dynamics in the gut during the gonadotrophic cycle. Small RNA libraries were constructed from female mosquito gut tissues at five time points. Unsupervised hierarchical clustering revealed three expression clusters (early, mid and late) peaking at sequential time points - 24, 48 and 72 h posteclosion. Differentially expressed miRNAs were identified at 24 h post-blood meal (PBM). Depletions of Methoprene-tolerant [Met; the juvenile hormone (JH) receptor] and Ecdysone receptor [EcR; the receptor to 20-hydroxyecdysone (20E)] were performed using dsRNA to these genes to investigate impacts on microRNA expressions. Our results suggest that Met-mediated signalling downregulates miRNA expression from the early cluster and upregulates that from the late cluster. EcR signalling either up- or downregulated miRNA levels at 24 h PBM, indicating a differential effect of this receptor in miRNA gene expression. Furthermore, miR-281, which is the most abundant miRNA in the gut tissue, is induced and repressed by Met- and EcR-mediated signalling, respectively. Systematic depletion using synthetic antagomir and phenotype examinations indicate that miR-281 is obligatory for the normal progression of blood digestion, ovarian development and reproduction. Collectively, this study unveils expression dynamics of microRNAs in the female gut tissue during the gonadotrophic cycle and demonstrates that they are affected by JH and 20E signalling.

Involvement of mind the gap in the organization of the tracheal apical extracellular matrix in Drosophila and Nilaparvata lugens

The tracheal apical extracellular matrix (aECM) is vital for expansion of the tracheal lumen and supports the normal structure of the lumen to guarantee air entry and circulation in insects. Although it has been found that some cuticular proteins are involved in the organization of the aECM, unidentified factors still exist. Here, we found that mind the gap (Mtg), a predicted chitin-binding protein, is required for the normal formation of the apical chitin matrix of airway tubes in the model holometabolous insect Drosophila melanogaster. Similar to chitin, the Mtg protein was linearly arranged in the tracheal dorsal trunk of the tracheae in Drosophila. Decreased mtg expression in the tracheae seriously affected the viability of larvae and caused tracheal chitin spiral defects in some larvae. Analysis of mtg mutant showed that mtg was required for normal development of tracheae in embryos. Irregular taenidial folds of some mtg mutant embryos were found on either lateral view of tracheal dorsal trunk or internal view of transmission electron microscopy analysis. These abnormal tracheae were not fully filled with gas and accompanied by a reduction in tracheal width, which are characteristic phenotypes of tracheal aECM defects. Furthermore, in the hemimetabolous brown planthopper (BPH) Nilaparvata lugens, downregulation of NlCPAP1-N (a homolog of mtg) also led to the formation of abnormal tracheal chitin spirals and death. These results suggest that mtg and its homolog are involved in the proper organization of the tracheal aECMs in flies and BPH, and that this function may be conserved in insects.

MicroRNA-277 regulates dopa decarboxylase to control larval-pupal and pupal-adult metamorphosis of Helicoverpa armigera

Insect metamorphosis is a complex process involving many metabolic pathways, such as juvenile hormones and molting hormones, bioamines, microRNAs (miRNAs), etc. However, relatively little is known about the biogenic amines and their miRNAs to regulate cotton bollworm metamorphosis. Here we show that one miRNA, miR-277 regulates larval-pupal and pupal-adult metamorphosis of cotton bollworm by targeting the 3'UTR of Dopa decarboxylase (DDC), a synthetic catalytic enzyme of dopamine. Injection of miR-277 agomir inhibited the expression of DDC at the mRNA and protein levels, leading to defects in the pupation and emergence of H. armigera that was consistent with the phenotype obtained by injection of DDC double-stranded RNA (dsRNA). Injection of miR-277 antagomir induced the mRNA and protein expression of DDC and rescued the phenotype of pupation failure caused by DDC gene silencing. Unexpectedly, miR-277 antagomir can also cause failure of emergence of H. armigera and both agomir and antagomir of miR-277 injection could cause abnormal phenotypes in wing veins. This study reveals that elaborate regulation of miRNA and its target gene expression is prerequisite for insect development, which provides a new insight to study the developmental mechanisms of insect wing veins.

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.

Transcriptome-Wide Identification of MicroRNAs and Analysis of Their Potential Roles in Development of Indian Meal Moth (Lepidoptera:Pyralidae)

MicroRNAs (miRNAs) have been reported to play indispensable roles in regulating various developmental processes via the posttranscriptional repression of target genes in insect species. In the present paper, we studied the miRNAs in Indian meal moth (Plodia interpunctella (Hübener)), one of the most economically important stored grains pests around the world. In total, 12 small RNA libraries from four developmental stages of P. interpunctella were constructed, and 178 known and 23 novel miRNAs were identified. In addition, the expression profiles of these miRNAs were assessed across different developmental stages and miRNAs that were highly expressed in eggs, larvae, pupae, and adults were identified. Specifically, 100, 61, and 52 miRNAs were differentially expressed between eggs and larvae, larvae and pupae, and pupae and adults, respectively. The KEGG and GO analysis of the predicted target genes suggested the essential roles of miRNAs in the regulation of complex development of P. interpunctella. Importantly, we also found a set of miRNAs might be involved in the larval metamorphic molting process, with their expressions increasing and then decreasing during the larva-pupa-adult stages of P. interpunctella. In conclusion, the current paper has discovered numerous miRNAs, and some key miRNAs that might be responsible for regulating development in P. interpunctella. To our knowledge, this is the first study to document miRNAs and their expression patterns in interpunctella, and those findings would lay an important molecular foundation for future functional analysis of these miRNAs in P. interpunctella.

Post-transcriptional regulation of insect metamorphosis and oogenesis

Metamorphic transformation from larvae to adults along with the high fecundity is key to insect success. Insect metamorphosis and reproduction are governed by two critical endocrines, juvenile hormone (JH), and 20-hydroxyecdysone (20E). Recent studies have established a crucial role of microRNA (miRNA) in insect metamorphosis and oogenesis. While miRNAs target genes involved in JH and 20E-signaling pathways, these two hormones reciprocally regulate miRNA expression, forming regulatory loops of miRNA with JH and 20E-signaling cascades. Insect metamorphosis and oogenesis rely on the coordination of hormones, cognate genes, and miRNAs for precise regulation. In addition, the alternative splicing of genes in JH and 20E-signaling pathways has distinct functions in insect metamorphosis and oogenesis. We, therefore, focus in this review on recent advances in post-transcriptional regulation, with the emphasis on the regulatory role of miRNA and alternative splicing, in insect metamorphosis and oogenesis. We will highlight important new findings of miRNA interactions with hormonal signaling and alternative splicing of JH receptor heterodimer gene Taiman.

Identification and Functional Analysis of Two Chitin Synthase Genes in the Common Cutworm, Spodoptera litura

Chitin is one the main components of the insect cuticle, and chitin synthase (CHS) is an important enzyme required for chitin formation. CHS has been characterized in various insect species, but the structure and biochemical properties in Spodoptera litura have not been determined. In this study, we identified two CHS genes, SlCHS1 and SlCHS2, which encode proteins with 1565 and 1520 amino acid residues, respectively. Transcriptional analysis suggested that SlCHS1 has a high expression level in the integument whereas SlCHS2 showed the highest expression level in the midgut. During S. litura growth and development, SlCHS1 and SlCHS2 were both predominantly expressed in the fourth-instar larval stage. In addition, the expression of SlCHS1 and SlCHS2 could be induced by 20-hydroxyecdysone (20E). Silencing of SlCHS1 by RNA interference significantly inhibited the pupation and molting of S. litura larvae (RNAi), while knockdown of SlCHS2 had no significant effects on the S. litura phenotype. These results may provide a new molecular target for control of S. litura.

miR-2703 regulates the chitin biosynthesis pathway by targeting chitin synthase 1a in Nilaparvata lugens

The chitin biosynthesis pathway is an important physiology process in arthropods. However, few microRNAs (miRNAs) involved in the regulation of the chitin biosynthesis pathway in insects have been reported until now. In this study, four groups of samples that either upregulated or downregulated the chitin biosynthesis pathway were collected for deep sequencing, and a total of 15 unique mature miRNAs with significantly different expression levels were found, including 11 known miRNAs and four novel miRNAs. Subsequently, we showed that miR-2703 and its new target gene chitin synthase 1a are important for ecdysone-induced chitin biosynthesis in Nilaparvata lugens, a serious insect pest of rice. The nymphs showed an obvious moulting defect phenotype, lower survival rate and significantly reduced chitin content after miR-2703 feeding or injection. Furthermore, we found that the transcription level of miR-2703 was not repressed by 20-hydroxyecdysone signalling after Broad-Complex (BR-C) double-stranded RNA (dsRNA) injection compared with the repressed levels after green fluorescent protein dsRNA injection, suggesting that the involvement of miR-2703 in the 20-hydroxyecdysone pathway contributes to BR-C activity. miR-2703 regulates the chitin biosynthesis pathway by targeting chitin synthase 1a in response to 20-hydroxyecdysone signalling.