Targeting the microRNA pathway core genes, Dicer 1 and Argonaute 1, negatively affects the survival and fecundity of Bemisia tabaci

A small RNA effector conserved in herbivore insects suppresses host plant defense by cross-kingdom gene silencing

Herbivore insects deploy salivary effectors to manipulate the defense of their host plants. However, it remains unclear whether small RNAs from insects can function as effectors in regulating plant-insect interactions. Here, we report that a microRNA (miR29-b) found in the saliva of the phloem-feeding whitefly (Bemisia tabaci) can transfer into the host plant phloem during feeding and fine-tune the defense response of tobacco (Nicotiana tabacum) plants. We show that the salivary gland-enriched BtmiR29-b is produced by BtDicer 1 and released into tobacco cells via salivary exosomes. Once inside the plant cells, BtmiR29-b hijacks tobacco Argonaute 1 to silence the defense gene Bcl-2-associated athanogene 4 (NtBAG4). In tobacco, NtBAG4 acts as the positive regulator of phytohormones salicylic acid (SA) and jasmonic acid (JA), enhancing plant defense against whitefly attacks. Interestingly, we also found that miR29-b acts as a salivary effector in another Hemipteran insect, the aphid Myzus persicae, which inhibits tobacco resistance by degrading NtBAG4. Moreover, miR29-b is highly conserved in Hemiptera and across other insect orders such as Coleoptera, Hymenoptera, Orthoptera, and Blattaria. Computational analysis suggests that miR29-b may also target the evolutionarily conserved BAG4 gene in other plant species. We further provide evidence showing BtmiR29-b-mediated BAG4 cleavage and defense suppression in tomato (Solanum lycopersicum). Taken together, our work reveals that a conserved miR29-b effector from insects fine-tunes plant SA- and JA-mediated defense by cross-kingdom silencing of the host plant BAG4 gene, providing new insight into the defense and counter-defense mechanisms between herbivores and their host plants.

MicroRNAs in the developmental toolbox - a comparative approach to understanding their role in regulating insect development

MicroRNAs are ubiquitous in the genomes of metazoans. Since their discovery during the late 20th century, our understanding of these small, noncoding RNAs has grown rapidly. However, there are still many unknowns about the functional significance of miRNAs - especially in non-model insects. Here I discuss the accumulating evidence that microRNAs are part of gene regulatory networks that determine not only the developmental outcome but also mediate transitions between stages and alternative developmental pathways. During the last 20 years, researchers have published a multitude of profiling studies that describe changes in miRNAs that may be important for development and catalog potential targets. Proof-of-principle studies document phenotypic changes that occur when candidate genes and/or miRNAs are inhibited or overexpressed. Studies that use both of these approaches, along with methods for confirming miRNA-mRNA interaction, demonstrate the necessary roles for miRNAs within gene networks. Together, all of these types of studies provide essential clues for understanding the function of miRNAs in the developmental toolbox.

Identification and function of microRNAs in hemipteran pests: A review

Hemiptera is one of the most significant orders of insect pests, including whiteflies, true bugs, aphids, planthoppers, psyllids, and so forth, which have led to substantial economic losses in agricultural industries and have significantly affected food yields through their ability to suck the phloem sap of crops and transmit numerous bacterial and viral pathogens. Therefore, explorations of pest-specific, eco-friendly and easy-to-adopt technologies for hemipteran pest control are urgently needed. To the best of our knowledge, microRNAs (miRNAs), which are endogenous non-coding small RNAs approximately 22 nucleotides in length, are involved in regulating gene expression via the direct recognition and binding of the 3'-untranslated region (3'-UTR) of target messenger RNAs (mRNAs) or by acting as a center of a competitive endogenous RNA (ceRNA) network at the post-transcriptional level. This review systematically outlines the characterization and functional investigation of the miRNA biogenesis pathway in hemipteran pests, such as whiteflies, true bugs, aphids and planthoppers. In addition, we explored the results of small RNA sequencing and functional observations of miRNAs in these pests, and the results suggest that the numerous miRNAs obtained and annotated via high-throughput sequencing technology and bioinformatic analyses contribute to molting development, fitness, wing polyphenism, symbiont interactions and insecticide resistance in hemipteran pests. Finally, we summarize current advances and propose a framework for future research to extend the current data and address potential limitations in the investigation and application of hemipteran miRNAs.

Disruption of microRNA pathway core genes inhibits molting and reproduction of the cigarette beetle, Lasioderma serricorne

BACKGROUND

MicroRNA (miRNA) pathway genes have been widely reported to participate in several physiological events in insect lifecycles. The cigarette beetle Lasioderma serricorne is an economically important storage pest worldwide. However, the functions of miRNA pathway genes in L. serricorne remain to be clarified. Herein, we investigated the function of molting and reproduction of the miRNA pathway in L. serricorne.

RESULTS

LsDicer-1, LsArgonaute-1, LsLoquacious and LsExportin-5 were universally expressed in adults, whereas LsPasha and LsDrosha were mainly expressed in the pupae. The genes presented different patterns in various tissues. Silencing of LsDicer-1, LsArgonaute-1, LsDrosha and LsExportin-5 resulted in a high proportion of wing deformities and molting defects. Silencing of LsDicer-1, LsArgonaute-1, LsPasha and LsLoquacious affected the development of the ovary and the maturation of oocytes, resulting in a significant decrease in fecundity. Further investigation revealed that the decreases in LsDicer-1 and LsArgonaute-1 expression destroyed follicular epithelia and delayed vitellogenesis and oocyte development. In addition, the expression levels of several miRNAs (let-7, let-7-5p, miR-8-3p, miR-8-5p, miR-9c-5p, miR-71, miR-252-5p, miR-277-3p, miR-263b and Novel-miR-50) were decreased significantly after knockdown of these miRNA pathway core genes, indicating that they played important roles in regulating miRNA-mediated gene expression.

CONCLUSION

The results indicate that miRNA pathway genes play important roles in the molting, ovarian development and female fecundity of L. serricorne, and thus are potentially suitable target genes for developing an RNAi strategy against a major pest of stored products. © 2024 Society of Chemical Industry.

Whitefly-Plant Interactions: An Integrated Molecular Perspective

The rapid advances in available transcriptomic and genomic data and our understanding of the physiology and biochemistry of whitefly-plant interactions have allowed us to gain new and significant insights into the biology of whiteflies and their successful adaptation to host plants. In this review, we provide a comprehensive overview of the mechanisms that whiteflies have evolved to overcome the challenges of feeding on phloem sap. We also highlight the evolution and functions of gene families involved in host perception, evaluation, and manipulation; primary metabolism; and metabolite detoxification. We discuss the emerging themes in plant immunity to whiteflies, focusing on whitefly effectors and their sites of action in plant defense-signaling pathways. We conclude with a discussion of advances in the genetic manipulation of whiteflies and the potential that they hold for exploring the interactions between whiteflies and their host plants, as well as the development of novel strategies for the genetic control of whiteflies.

Role of miR-276-3p in the cyantraniliprole resistance mechanism of Bemisia tabaci via CYP6CX3 targeting

The sweet potato whitefly, Bemisia tabaci, is an important insect pest that transmits over 200 different plant viruses and causes serious damage to the production of cotton and Solanaceae vegetables. Cyantraniliprole is the first diamide insecticide, showing toxicity against B. tabaci. However, B. tabaci has developed resistance to this insecticide by upregulating the expressions of cytochrome P450 genes such as CYP6CX3, while there is limited information on the regulatory mechanism mediated by miRNA. In the present study, ten miRNAs were predicted to target CYP6CX3, in which miR-276-3p showed an inverse expression pattern with CYP6CX3 in two cyantraniliprole resistant strains and under cyantraniliprole exposure. A luciferase assay demonstrated that miR-276-3p suppressed CYP6CX3 expression by pairing with residues 1445-1453. Overexpression or knockdown of miR-276-3p directly impacted B. tabaci resistance to cyantraniliprole. In addition, exposure to cyantraniliprole led to a significant reduction in the expressions of five genes (drosha, dicer1, dicer2, Ago1, and Ago2A) associated with miRNA biogenesis. Suppressing genes such as drosha, dicer1, and Ago2A reduced the expression of miR-276-3p, increased CYP6CX3 expression, and decreased B. tabaci resistance to cyantraniliprole. These results improve our understanding of the role of miRNAs in P450 regulation and cyantraniliprole resistance in B. tabaci.

The microRNA pathway core genes are indispensable for development and reproduction in the brown planthopper, Nilaparvata lugens

MicroRNAs (miRNAs) are small single-stranded non-coding RNAs involved in a variety of cellular events by regulating gene expression at the post-transcriptional level. Several core genes in miRNA biogenesis have been reported to participate in a wide range of physiological events, in some insect species. However, the functional significance of miRNA pathway core genes in Nilaparvata lugens remains unknown. In the present study, we conducted a systematic characterisation of five core genes involved in miRNA biogenesis. We first performed spatiotemporal expression analysis and found that miRNA core genes exhibited similar expression patterns, with high expression levels in eggs and relatively high transcriptional levels in the ovaries and fat bodies of females. RNA interference experiments showed that injecting third-instar nymphs with dsRNAs targeting the miRNA core genes, NlAgo1, NlDicer1, and NlDrosha resulted in high mortality rates and various degrees of body melanism, moulting defects, and wing deformities. Further investigations revealed that the suppression of miRNA core genes severely impaired ovarian development and oocyte maturation, resulting in significantly reduced fecundity and disruption of intercellular spaces between follicle cells. Moreover, the expression profiles of miR-34-5p, miR-275-3p, miR-317-3p, miR-14, Let-7-1, and miR-2a-3p were significantly altered in response to the knockdown of miRNA core genes mixture, suggesting that they play essential roles in regulating miRNA-mediated gene expression. Therefore, our results provide a solid theoretical basis for the miRNA pathway in N. lugens and suggest that the NlAgo1, NlDicer1, and NlDrosha-dependent miRNA core genes are essential for the development and reproduction of this agricultural pest.

SfDicer1 participates in the regulation of molting development and reproduction in the white-backed planthopper, Sogatella furcifera

Dicer1 plays a vital role in the formation of mature miRNA and regulates the growth, development, and reproduction of insects. However, it remains to be clarified whether Dicer1 is involved in regulating the biological processes underlying molting and reproduction of Sogatella furcifera (Horváth). Herein, SfDicer1 expression fluctuated in all the developmental stages of S. furcifera and increased as molting progressed. SfDicer1 exhibited high expression in the integument, head, fat body, and ovary of the insects. SfDicer1 dsRNA injection into 1-day-old fourth instar nymphs of S. furcifera substantially decreased the survival rate and expression of the lethal phenotypes of wing malformation and molting defects and significantly inhibited the expression of four conserved miRNAs associated with molting development. Subsequently, following the knockdown of SfDicer1 in the newly emerged (1-12 h) females of S. furcifera, SfVg and SfVgR expression levels were decreased, thereby delaying ovarian development, decreasing the number of eggs, and considerably reducing the hatching rate compared with those of the control. Finally, after silencing SfDicer1 for 48 h, the comparative transcriptome analysis of differentially expressed genes revealed considerable enrichment of the Gene Ontology terms structural constituent of cuticle, structural molecule activity, chitin metabolic process, amino sugar metabolic process, and intracellular anatomical structure, indicating that SfDicer1 inhibition affects the transcription of genes associated with growth and development. Thus, our results suggest that SfDicer1 is essential in the molting, survival, ovarian development, and fecundity of S. furcifera and is a suitable target gene for developing an RNAi-based strategy targeting the most destructive rice insect pest.