The draft genome of whitefly Bemisia tabaci MEAM1, a global crop pest, provides novel insights into virus transmission, host adaptation, and insecticide resistance

Transcriptome data reveal beneficial effects of Rickettsia (Rickettsiales: Rickettsiaceae) on Bemisia tabaci(Hemiptera: Aleyrodidae) through nutritional factors and defense mechanisms

Whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is a destructive insect pest of many crops. Rickettsia infection in different cryptic species of B. tabaci has been observed worldwide. Understanding the interactions between these 2 organisms is critical to developing Rickettsia-based strategies to control B. tabaci and thereby reduce the transmission of related vector-borne viruses. In this study, we investigated the effects of Rickettsia infection on the biological characteristics of the Middle East Asia Minor 1 (MEAM1) strain of B. tabaci through biological analysis of infected and uninfected individuals. The results of this study suggest that Rickettsia may confer fitness benefits. These benefits include increased fertility, improved survival rates, accelerated development, and resulted in female bias. We also investigated the transcriptomics impact of Rickettsia infection on B. tabaci by performing a comparative RNA-seq analysis of nymphs and adult females, both with and without the infection. Our analysis revealed 218 significant differentially expressed genes (DEGs) in infected nymphs compared to uninfected ones and 748 significant DEGs in infected female adults compared to their uninfected whiteflies. Pathway analysis further revealed that Rickettsia can affect many important metabolic pathways in whiteflies. The results suggest that Rickettsia plays an essential role in energy metabolism, and nutrient synthesis in the B. tabaci MEAM1, and depends on metabolites obtained from the host to ensure its survival. Overall, our findings suggest that Rickettsia has beneficial effects on B. tabaci and offered insights into the potential molecular mechanisms governing the interactions between Rickettsia and B. tabaci MEAM1.

Wolbachia symbionts control sex in a parasitoid wasp using a horizontally acquired gene

Host reproduction can be manipulated by bacterial symbionts in various ways. Parthenogenesis induction is the most effective type of reproduction manipulation by symbionts for their transmission. Insect sex is determined by regulation of doublesex (dsx) splicing through transformer2 (tra2) and transformer (tra) interaction. Although parthenogenesis induction by symbionts has been studied since the 1970s, its underlying molecular mechanism is unknown. Here we identify a Wolbachia parthenogenesis-induction feminization factor gene (piff) that targets sex-determining genes and causes female-producing parthenogenesis in the haplodiploid parasitoid Encarsia formosa. We found that Wolbachia elimination repressed expression of female-specific dsx and enhanced expression of male-specific dsx, which led to the production of wasp haploid male offspring. Furthermore, we found that E. formosa tra is truncated and non-functional, and Wolbachia has a functional tra homolog, termed piff, with an insect origin. Wolbachia PIFF can colocalize and interact with wasp TRA2. Moreover, Wolbachia piff has coordinated expression with tra2 and dsx of E. formosa. Our results demonstrate the bacterial symbiont Wolbachia has acquired an insect gene to manipulate the host sex determination cascade and induce parthenogenesis in wasps. This study reveals insect-to-bacteria horizontal gene transfer drives the evolution of animal sex determination systems, elucidating a striking mechanism of insect-microbe symbiosis.

CRISPR/Cas9-Based Functional Characterization of SfUGT50A15 Reveals Its Roles in the Resistance of Spodoptera frugiperda to Chlorantraniliprole, Emamectin Benzoate, and Benzoxazinoids

UDP-glycosyltransferases (UGTs) are a diverse superfamily of enzymes. Insects utilize uridine diphosphate-glucose (UDP-glucose) as a glycosyl donor for glycosylation in vivo, involved in the glycosylation of lipophilic endosymbionts and xenobiotics, including phytotoxins. UGTs act as second-stage detoxification metabolizing enzymes, which are essential for the detoxification metabolism of insecticides and benzoxazine compounds. However, the UGT genes responsible for specific glycosylation functions in S. frugiperda are unclear at present. In this study, we utilized CRISPR/Cas9 to produce a SfUGT50A15-KO strain to explore its possible function in governing sensitivity to chemical insecticides or benzoxazinoids. The bioassay results suggested that the SfUGT50A15-KO strain was significantly more sensitive to chlorantraniliprole, emamectin benzoate, and benzoxazinoids than the wild-type strains. This finding suggests that the overexpression of the SfUGT50A15 gene may be linked to S. frugiperda resistance to pesticides (chlorantraniliprole and emamectin benzoate) as well as benzoxazinoids (BXDs).

A comprehensive framework for the delimitation of species within the Bemisia tabaci cryptic complex, a global pest-species group

Identifying cryptic species poses a substantial challenge to both biologists and naturalists due to morphological similarities. Bemisia tabaci is a cryptic species complex containing more than 44 putative species; several of which are currently among the world's most destructive crop pests. Interpreting and delimiting the evolution of this species complex has proved problematic. To develop a comprehensive framework for species delimitation and identification, we evaluated the performance of distinct data sources both individually and in combination among numerous samples of the B. tabaci species complex acquired worldwide. Distinct datasets include full mitogenomes, single-copy nuclear genes, restriction site-associated DNA sequencing, geographic range, host speciation, and reproductive compatibility datasets. Phylogenetically, our well-supported topologies generated from three dense molecular markers highlighted the evolutionary divergence of species of the B. tabaci complex and suggested that the nuclear markers serve as a more accurate representation of B. tabaci species diversity. Reproductive compatibility datasets facilitated the identification of at least 17 different cryptic species within our samples. Native geographic range information provides a complementary assessment of species recognition, while the host range datasets provide low rate of delimiting resolution. We further summarized different data performances in species classification when compared with reproductive compatibility, indicating that combination of mtCOI divergence, nuclear markers, geographic range provide a complementary assessment of species recognition. Finally, we represent a model for understanding and untangling the cryptic species complexes based on the evidence from this study and previously published articles.

Discovery of Three Bemisia tabaci Effectors and Their Effect on Gene Expression in Planta

Bemisia tabaci (whitefly) is a polyphagous agroeconomic pest species complex. Two members of this species complex, Mediterranean (MED) and Middle-East-Asia Minor 1 (MEAM1), have a worldwide distribution and have been shown to manipulate plant defenses through effectors. In this study, we used three different strategies to identify three MEAM1 proteins that can act as effectors. Effector B1 was identified using a bioinformatics-driven effector-mining strategy, whereas effectors S1 and P1 were identified in the saliva of whiteflies collected from artificial diet and in phloem exudate of tomato on which nymphs were feeding, respectively. These three effectors were B. tabaci specific and able to increase whitefly fecundity when transiently expressed in tobacco plants (Nicotiana tabacum). Moreover, they reduced growth of Pseudomonas syringae pv. tabaci in Nicotiana benthamiana. All three effectors changed gene expression in planta, and B1 and S1 also changed phytohormone levels. Gene ontology and KEGG pathway enrichment analysis pinpointed plant-pathogen interaction and photosynthesis as the main enriched pathways for all three effectors. Our data thus show the discovery and validation of three new B. tabaci MEAM1 effectors that increase whitefly fecundity and modulate plant immunity. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Uridine diphosphate glucosyltransferases are involved in spinosad resistance in western flower thrips Frankliniella occidentalis (Pergande)

Uridine diphosphate glucosyltransferases (UGTs) play crucial roles in the insect detoxification system and are associated with pesticide resistance. Our previous transcriptomic analysis of spinosad-susceptible (Ivf03) and resistant (NIL-R) Frankliniella occidentalis revealed numerous upregulated UGT genes in the NIL-R strain, suggesting their potential contribution to spinosad resistance. To investigate this hypothesis, here we conducted UGT activity assays and spinosad induction experiments, employing RNA interference (RNAi) techniques for gene function validation. We found significantly elevated UGT activity in the NIL-R strain compared to Ivf03, with 5-nitrouracil showing a substantial synergistic effect on the resistant strain. Eighteen UGT genes were identified in F. occidentalis, with gene expansion and duplication observed within families UGT466, 467, and 468. Ten out of the eighteen UGTs exhibited higher expression levels in NIL-R, specifically FoUGT466B1, FoUGT468A3, and FoUGT468A4 consistently being upregulated across nymphs, males, and females. RNAi-based functional validation targeting these three UGT genes led to increased susceptibility to spinosad in a life stage-, sex-, and dose-dependent manner. These results indicate that UGTs are indeed involved in spinosad resistance in F. occidentalis, and the effects are dependent on life stage, sex, and dose. Therefore, sustainable control for F. occidentalis resistance should always consider these differential responses.

An association between Dnmt1 and Wnt in the production of oocytes in the whitefly Bemisia tabaci

The function of DNA methylation in insects and the DNA methyltransferase (Dnmt) genes that influence methylation remains uncertain. We used RNA interference to reduce the gene expression of Dnmt1 within the whitefly Bemisia tabaci (Hemiptera:Aleyrodidae; Gennadius), a hemipteran species that relies on Dnmt1 for proper gametogenesis. We then used RNA-seq to test an a priori hypothesis that meiosis-related genetic pathways would be perturbed. We generally did not find an overall effect on meiosis-related pathways. However, we found that genes in the Wnt pathway, genes associated with the entry into meiosis in vertebrates, were differentially expressed. Our results are consistent with Dnmt1 knockdown influencing specific pathways and not causing general transcriptional response. This is a finding that is also seen with other insect species. We also characterised the methylome of B. tabaci and assessed the influence of Dnmt1 knockdown on cytosine methylation. This species has methylome characteristics comparable to other hemipterans regarding overall level, enrichment within gene bodies, and a bimodal distribution of methylated/non-methylated genes. Very little differential methylation was observed, and difference in methylation were not associated with differences in gene expression. The effect on Wnt presents an interesting new candidate pathway for future studies.

Genomic and Transcriptomic Insights into the Genetic Basis of Foam Secretion in Rice Spittlebug Callitettix versicolor

Many animal species produce protective foams, the majority of which exhibit evolutionary adaptability. Although the function and composition of foams have been widely studied, the genetic basis of foam secretion remains unknown. Unlike most species that produce foam under specific situations, spittlebugs continuously secrete foams throughout all nymphal stages. Here, we capitalize on the rice spittlebug (Callitettix versicolor) to explore the genetic basis of foam secretion through genomic and transcriptomic approaches. Our comparative genomic analysis for C. versicolor and eight other insect species reveals 606 species-specific gene families and 66 expanded gene families, associated with carbohydrate and lipid metabolism. These functions are in accordance with the composition of foams secreted by spittlebugs. Transcriptomic analyses of malpighian tubules across developmental stages detected 3192 differentially expressed genes. Enrichment analysis of these genes highlights functions also revealed by our comparative genomic analysis and aligns with previous histochemical and morphological observations of foam secretion. This consistency suggests the important roles of these candidate genes in foam production. Our study not only provides novel insights into the genetic basis of foam secretion in rice spittlebugs but also contributes valuable knowledge for future evolutionary studies of spittlebugs and the development of pest control strategies for C. versicolor.

Dual mutations in the whitefly nicotinic acetylcholine receptor β1 subunit confer target-site resistance to multiple neonicotinoid insecticides

Neonicotinoid insecticides, which target insect nicotinic acetylcholine receptors (nAChRs), have been widely and intensively used to control the whitefly, Bemisia tabaci, a highly damaging, globally distributed, crop pest. This has inevitably led to the emergence of populations with resistance to neonicotinoids. However, to date, there have been no reports of target-site resistance involving mutation of B. tabaci nAChR genes. Here we characterize the nAChR subunit gene family of B. tabaci and identify dual mutations (A58T&R79E) in one of these genes (BTβ1) that confer resistance to multiple neonicotinoids. Transgenic D. melanogaster, where the native nAChR Dβ1 was replaced with BTβ1A58T&R79E, were significantly more resistant to neonicotinoids than flies where Dβ1 were replaced with the wildtype BTβ1 sequence, demonstrating the causal role of the mutations in resistance. The two mutations identified in this study replace two amino acids that are highly conserved in >200 insect species. Three-dimensional modelling suggests a molecular mechanism for this resistance, whereby A58T forms a hydrogen bond with the R79E side chain, which positions its negatively-charged carboxylate group to electrostatically repulse a neonicotinoid at the orthosteric site. Together these findings describe the first case of target-site resistance to neonicotinoids in B. tabaci and provide insight into the molecular determinants of neonicotinoid binding and selectivity.

Chromosome-level genome assembly of the Asian citrus psyllid, Diaphorina citri

Diaphorina citri is a global citrus pest. As a vector insect, it can transmit the causative agents of citrus huanglongbing, causing irreversible losses to the citrus industry. The acquisition of genomic information can provide a molecular genetic basis for effective control of D. citri. Here, the DNBSEQ™ , Oxford Nanopore Technologies, and Hi-C technologies are applied to generate a high-quality chromosome-level genome of D. citri. The genome size of D. citri was 523.78 Mb with a scaffold N50 of 47.05 Mb distributed on 13 chromosomes. A total of 250.64 Mb (47.85%) repeat sequences and 24 048 protein-coding genes were predicted. Genome resequencing of female and male individuals indicated that the sex chromosome system of D. citri is XO. Phylogenetic analysis demonstrated that D. citri and Pachypsylla venusta, which separated from their most recent common ancestor about 336.62 million years ago, were the most closely related. Additionally, we identified genes potentially involved in detoxification metabolism, pathogen transmission, and honeydew secretion for further investigation. The high-quality genome provides an important reference for developing effective management strategies of D. citri.

Interaction of Whitefly Effector G4 with Tomato Proteins Impacts Whitefly Performance

The phloem-feeding insect Bemisia tabaci is an important pest, responsible for the transmission of several crop-threatening virus species. While feeding, the insect secretes a cocktail of effectors to modulate plant defense responses. Here, we present a set of proteins identified in an artificial diet on which B. tabaci was salivating. We subsequently studied whether these candidate effectors can play a role in plant immune suppression. Effector G4 was the most robust suppressor of an induced- reactive oxygen species (ROS) response in Nicotiana benthamiana. In addition, G4 was able to suppress ROS production in Solanum lycopersicum (tomato) and Capsicum annuum (pepper). G4 localized predominantly in the endoplasmic reticulum in N. benthamiana leaves and colocalized with two identified target proteins in tomato: REF-like stress related protein 1 (RSP1) and meloidogyne-induced giant cell protein DB141 (MIPDB141). Silencing of MIPDB141 in tomato reduced whitefly fecundity up to 40%, demonstrating that the protein is involved in susceptibility to B. tabaci. Together, our data demonstrate that effector G4 impairs tomato immunity to whiteflies by interfering with ROS production and via an interaction with tomato susceptibility protein MIPDB141. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

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.

The evolutionary trajectories of specialized metabolites towards antiviral defense system in plants

Viral infections in plants pose major challenges to agriculture and global food security in the twenty-first century. Plants have evolved a diverse range of specialized metabolites (PSMs) for defenses against pathogens. Although, PSMs-mediated plant-microorganism interactions have been widely discovered, these are mainly confined to plant-bacteria or plant-fungal interactions. PSM-mediated plant-virus interaction, however, is more complicated often due to the additional involvement of virus spreading vectors. Here, we review the major classes of PSMs and their emerging roles involved in antiviral resistances. In addition, evolutionary scenarios for PSM-mediated interactions between plant, virus and virus-transmitting vectors are presented. These advancements in comprehending the biochemical language of PSMs during plant-virus interactions not only lay the foundation for understanding potential co-evolution across life kingdoms, but also open a gateway to the fundamental principles of biological control strategies and beyond.

The role of the Bemisia tabaci and Trialeurodes vaporariorum cytochrome-P450 clade CYP6DPx in resistance to nicotine and neonicotinoids

The alkaloid, nicotine, produced by tobacco and other Solanaceae as an anti-herbivore defence chemical is one of the most toxic natural insecticides in nature. However, some insects, such as the whitefly species, Trialeurodes vaporariorum and Bemisia tabaci show strong tolerance to this allelochemical and can utilise tobacco as a host. Here, we used biological, molecular and functional approaches to investigate the role of cytochrome P450 enzymes in nicotine tolerance in T. vaporariorum and B. tabaci. Insecticide bioassays revealed that feeding on tobacco resulted in strong induced tolerance to nicotine in both species. Transcriptome profiling of both species reared on tobacco and bean hosts revealed profound differences in the transcriptional response these host plants. Interrogation of the expression of P450 genes in the host-adapted lines revealed that P450 genes belonging to the CYP6DP subfamily are strongly upregulated in lines reared on tobacco. Functional characterisation of these P450s revealed that CYP6DP1 and CYP6DP2 of T. vaporariorum and CYP6DP3 of B. tabaci confer resistance to nicotine in vivo. These three genes, in addition to the B. tabaci P450 CYP6DP5, were also found to confer resistance to the neonicotinoid imidacloprid. Our data provide new insight into the molecular basis of nicotine resistance in insects and illustrates how divergence in the evolution of P450 genes in this subfamily in whiteflies may have impacted the extent to which different species can tolerate a potent natural insecticide.

Characteristics of the Accessible Chromatin Landscape and Transcriptome under Different Temperature Stresses in Bemisia tabaci

Bemisia tabaci is an important invasive pest with worldwide distribution and strong temperature tolerance. Previous studies have shown that temperature tolerance varies significantly between the different invasive populations. Several key factors involved in epigenetic regulation have been identified and verified in B. tabaci; therefore, epigenetic adaptation mechanisms may also exist. This study aimed to detect changes in the chromatin accessibility landscape and genome-wide transcriptome under different temperature stresses in B. tabaci. Assay for transposase-accessible chromatin with high-throughput sequencing and RNA-seq analyses indicated that transcriptional activity of the genes strongly correlates with chromatin accessibility. Chromatin transcription-activated gene expression regulation is dominant during high-temperature stress in B. tabaci, mainly through the transcriptional repression of genes related to low-temperature stress resistance. Furthermore, B. tabaci resists low-temperature stress by regulating enzyme activities and withstands high-temperature stress by regulating metabolism and synthesis of organic substances, both achieved by altering chromatin accessibility. In summary, this study provides a theoretical basis for exploring changes in gene expression and chromatin accessibility under different temperature stresses, offering a new approach to unravelling regulatory mechanisms underlying the onset of molecular regulation in response to various temperature stress conditions.

Parallel Losses of Blue Opsin Correlate with Compensatory Neofunctionalization of UV-Opsin Gene Duplicates in Aphids and Planthoppers

Expanding on previous efforts to survey the visual opsin repertoires of the Hemiptera, this study confirms that homologs of the UV- and LW-opsin subfamilies are conserved in all Hemiptera, while the B-opsin subfamily is missing from the Heteroptera and subgroups of the Sternorrhyncha and Auchenorrhyncha, i.e., aphids (Aphidoidea) and planthoppers (Fulgoroidea), respectively. Unlike in the Heteroptera, which are characterized by multiple independent expansions of the LW-opsin subfamily, the lack of B-opsin correlates with the presence of tandem-duplicated UV-opsins in aphids and planthoppers. Available data on organismal wavelength sensitivities and retinal gene expression patterns lead to the conclusion that, in both groups, one UV-opsin paralog shifted from ancestral UV peak sensitivity to derived blue sensitivity, likely compensating for the lost B-opsin. Two parallel bona fide tuning site substitutions compare to 18 non-corresponding amino acid replacements in the blue-shifted UV-opsin paralogs of aphids and planthoppers. Most notably, while the aphid blue-shifted UV-opsin clade is characterized by a replacement substitution at one of the best-documented UV/blue tuning sites (Rhodopsin site 90), the planthopper blue-shifted UV-opsin paralogs retained the ancestral lysine at this position. Combined, the new findings identify aphid and planthopper UV-opsins as a new valuable data sample for studying adaptive opsin evolution.

The chromosome-scale reference genome of mirid bugs (Adelphocoris suturalis) genome provides insights into omnivory, insecticide resistance, and survival adaptation

BACKGROUND

Adelphocoris suturalis (Hemiptera: Miridae) is a notorious agricultural pest, which causes serious economic losses to a diverse range of agricultural crops around the world. The poor understanding of its genomic characteristics has seriously hindered the establishment of sustainable and environment-friendly agricultural pest management through biotechnology and biological insecticides.

RESULTS

Here, we report a chromosome-level assembled genome of A. suturalis by integrating Illumina short reads, PacBio, 10x Chromium, and Hi-C mapping technologies. The resulting 1.29 Gb assembly contains twelve chromosomal pseudomolecules with an N50 of 1.4 and 120.6 Mb for the contigs and scaffolds, respectively, and carries 20,010 protein-coding genes. The considerable size of the A. suturalis genome is predominantly attributed to a high amount of retrotransposons, especially long interspersed nuclear elements (LINEs). Transcriptomic and phylogenetic analyses suggest that A. suturalis-specific candidate effectors, and expansion and expression of gene families associated with omnivory, insecticide resistance and reproductive characteristics, such as digestion, detoxification, chemosensory receptors and long-distance migration likely contribute to its strong environmental adaptability and ability to damage crops. Additionally, 19 highly credible effector candidates were identified and transiently overexpressed in Nicotiana benthamiana for functional assays and potential targeting for insect resistance genetic engineering.

CONCLUSIONS

The high-quality genome of A. suturalis provides an important genomic landscape for further investigations into the mechanisms of omnivory, insecticide resistance and survival adaptation, and for the development of integrated management strategies.

Starving the Beast: Limiting Coenzyme A Biosynthesis to Prevent Disease and Transmission in Malaria

Malaria parasites must acquire all necessary nutrients from the vertebrate and mosquito hosts to successfully complete their life cycle. Failure to acquire these nutrients can limit or even block parasite development and presents a novel target for malaria control. One such essential nutrient is pantothenate, also known as vitamin B5, which the parasite cannot synthesize de novo and is required for the synthesis of coenzyme A (CoA) in the parasite. This review examines pantothenate and the CoA biosynthesis pathway in the human-mosquito-malaria parasite triad and explores possible approaches to leverage the CoA biosynthesis pathway to limit malaria parasite development in both human and mosquito hosts. This includes a discussion of sources for pantothenate for the mosquito, human, and parasite, examining the diverse strategies used by the parasite to acquire substrates for CoA synthesis across life stages and host resource pools and a discussion of drugs and alternative approaches being studied to disrupt CoA biosynthesis in the parasite. The latter includes antimalarial pantothenate analogs, known as pantothenamides, that have been developed to target this pathway during the human erythrocytic stages. In addition to these parasite-targeted drugs, we review studies of mosquito-targeted allosteric enzymatic regulators known as pantazines as an approach to limit pantothenate availability in the mosquito and subsequently deprive the parasite of this essential nutrient.

Identifying potential insecticide resistance markers through genomic-level comparison of Bemisia tabaci (Gennadius) lines

The invasive whitefly (Bemisia tabaci) MED is one of the most economically damaging plant pests. The extensive use of insecticide over decades has led to that the invasive B. tabaci MED has developed resistance to a wide range of insecticide classes, but little is known about the genetic background associated with resistance. To this end, we conducted a comparative genome-wide analysis of single-base nucleotide polymorphisms between MED whitefly lines collected from fields that were recently infested and an insecticide-susceptible MED whitefly line collected in 1976. First, low-coverage genome sequencings were conducted on DNA isolated from individual whiteflies. The sequencing results were evaluated using an available B. tabaci MED genome as a reference. Significant genetic differences were discovered between MED whitefly lines collected from fields that were recently infested and an insecticide-susceptible MED whitefly line based on the principal component analyses. Top GO categories and KEGG pathways that might be involved in insecticide resistance development were identified, and several of them have not been previously associated with resistance. Additionally, we identified several genetic loci with novel variations including Cytochrome P450 monooxygenases (P450s), UDP-glucuronosyltransferases (UGTs), Glutathione S-transferases (GSTs), esterase, carboxyl-esterases (COE), ABC transporters, fatty acyl-CoA reductase, voltage-gated sodium channels, GABA receptor, and cuticle proteins (CPs) that were previously reported to have close associations with pesticide resistance in well-studied insect groups that provide an essential resource for the design of insecticide resistance-linked loci arrays insecticide. Our results was obtained solely on resequencing genome data sets, more pesticide bio-assays combined with omics datasets should be further used to verify the markers identified here.

Comparative evolutionary analyses of eight whitefly Bemisia tabaci sensu lato genomes: cryptic species, agricultural pests and plant-virus vectors

BACKGROUND

The group of > 40 cryptic whitefly species called Bemisia tabaci sensu lato are amongst the world's worst agricultural pests and plant-virus vectors. Outbreaks of B. tabaci s.l. and the associated plant-virus diseases continue to contribute to global food insecurity and social instability, particularly in sub-Saharan Africa and Asia. Published B. tabaci s.l. genomes have limited use for studying African cassava B. tabaci SSA1 species, due to the high genetic divergences between them. Genomic annotations presented here were performed using the 'Ensembl gene annotation system', to ensure that comparative analyses and conclusions reflect biological differences, as opposed to arising from different methodologies underpinning transcript model identification.

RESULTS

We present here six new B. tabaci s.l. genomes from Africa and Asia, and two re-annotated previously published genomes, to provide evolutionary insights into these globally distributed pests. Genome sizes ranged between 616-658 Mb and exhibited some of the highest coverage of transposable elements reported within Arthropoda. Many fewer total protein coding genes (PCG) were recovered compared to the previously published B. tabaci s.l. genomes and structural annotations generated via the uniform methodology strongly supported a repertoire of between 12.8-13.2 × 10³ PCG. An integrative systematics approach incorporating phylogenomic analysis of nuclear and mitochondrial markers supported a monophyletic Aleyrodidae and the basal positioning of B. tabaci Uganda-1 to the sub-Saharan group of species. Reciprocal cross-mating data and the co-cladogenesis pattern of the primary obligate endosymbiont 'Candidatus Portiera aleyrodidarum' from 11 Bemisia genomes further supported the phylogenetic reconstruction to show that African cassava B. tabaci populations consist of just three biological species. We include comparative analyses of gene families related to detoxification, sugar metabolism, vector competency and evaluate the presence and function of horizontally transferred genes, essential for understanding the evolution and unique biology of constituent B. tabaci. s.l species.

CONCLUSIONS

These genomic resources have provided new and critical insights into the genetics underlying B. tabaci s.l. biology. They also provide a rich foundation for post-genomic research, including the selection of candidate gene-targets for innovative whitefly and virus-control strategies.

Pest status, molecular evolution, and epigenetic factors derived from the genome assembly of Frankliniella fusca, a thysanopteran phytovirus vector

BACKGROUND

The tobacco thrips (Frankliniella fusca Hinds; family Thripidae; order Thysanoptera) is an important pest that can transmit viruses such as the tomato spotted wilt orthotospovirus to numerous economically important agricultural row crops and vegetables. The structural and functional genomics within the order Thysanoptera has only begun to be explored. Within the > 7000 known thysanopteran species, the melon thrips (Thrips palmi Karny) and the western flower thrips (Frankliniella occidentalis Pergrande) are the only two thysanopteran species with assembled genomes.

RESULTS

A genome of F. fusca was assembled by long-read sequencing of DNA from an inbred line. The final assembly size was 370 Mb with a single copy ortholog completeness of ~ 99% with respect to Insecta. The annotated genome of F. fusca was compared with the genome of its congener, F. occidentalis. Results revealed many instances of lineage-specific differences in gene content. Analyses of sequence divergence between the two Frankliniella species' genomes revealed substitution patterns consistent with positive selection in ~ 5% of the protein-coding genes with 1:1 orthologs. Further, gene content related to its pest status, such as xenobiotic detoxification and response to an ambisense-tripartite RNA virus (orthotospovirus) infection was compared with F. occidentalis. Several F. fusca genes related to virus infection possessed signatures of positive selection. Estimation of CpG depletion, a mutational consequence of DNA methylation, revealed that F. fusca genes that were downregulated and alternatively spliced in response to virus infection were preferentially targeted by DNA methylation. As in many other insects, DNA methylation was enriched in exons in Frankliniella, but gene copies with homology to DNA methyltransferase 3 were numerous and fragmented. This phenomenon seems to be relatively unique to thrips among other insect groups.

CONCLUSIONS

The F. fusca genome assembly provides an important resource for comparative genomic analyses of thysanopterans. This genomic foundation allows for insights into molecular evolution, gene regulation, and loci important to agricultural pest status.

A C2H2 zinc finger transcription factor of the whitefly Bemisia tabaci interacts with the capsid proteins of begomoviruses and inhibits virus retention

Begomoviruses are a group of ssDNA viruses exclusively transmitted by the whitefly Bemisia tabaci and constrain vegetable production in the old and new worlds. Although multiple molecular determinants governing the transmission of begomoviruses by whiteflies have been unravelled, factors critical for transmission majorly remain unknown. In this study, a whitefly C2H2 zinc finger (ZF) protein, 100% identical to the vascular endothelial ZF-like gene (vezf) protein was confirmed to interact with the CP of both old- and new-world begomoviruses. This was achieved by a yeast two-hybrid (Y2H) system screening of a whitefly cDNA library using capsid protein (CP) of TYLCV as a bait. In silico annotation of vezf protein revealed that it contains a N-terminal ZF-associated domain (ZAD) alongside multiple C2H2 ZF domains on the C-terminal end. ZAD-ZF proteins form the most abundant class of transcription factors within insects. Herein, we validated the interaction of vezf with four diverse begomoviruses and its functional role in begomovirus transmission. Silencing of the vezf gene of B. tabaci led to increased retention of three diverse begomoviruses tested. Vezf is the first insect transcription factor identified to interact with plant viruses and can be crucial to understand the possible mechanisms by which plant viruses modulate transcription of their insect vectors during transmission.

The role of Dnmt1 in oocyte development

The whitefly Bemisia tabaci is a globally important crop pest that is difficult to manage through current commercially available methods. While RNA interference (RNAi) is a promising strategy for managing this pest, effective target genes remain unclear. We suggest DNA methyltransferase 1 (Dnmt1) as a potential target gene due to its effect on fecundity in females in other taxa of insects. We investigated the role of Dnmt1 in B. tabaci using RNAi and immunohistochemistry to confirm its potential conserved function in insect reproduction, which will define its usefulness as a target gene. Using RNAi to downregulate Dnmt1 in female B. tabaci, we show that Dnmt1 indeed has a conserved role in reproduction, as knockdown interfered with oocyte development. Females in which Dnmt1 was knocked down had greatly reduced fecundity and fertility; this supports Dnmt1 as a suitable target gene for RNAi-mediated pest management of B. tabaci.

A sucrose-specific receptor in Bemisia tabaci and its putative role in phloem feeding

In insects, specialized feeding on the phloem sap (containing mainly the sugar sucrose) has evolved only in some hemipteran lineages. This feeding behavior requires an ability to locate feeding sites buried deeply within the plant tissue. To determine the molecular mechanism involved, we hypothesized that the phloem-feeding whitefly Bemisia tabaci relies on gustatory receptor (GR)-mediated sugar sensing. We first conducted choice assays, which indicated that B. tabaci adults consistently choose diets containing higher sucrose concentrations. Next, we identified four GR genes in the B. tabaci genome. One of them, BtabGR1, displayed significant sucrose specificity when expressed in Xenopus oocytes. Silencing of BtabGR1 significantly interfered with the ability of B. tabaci adults to discriminate between non-phloem and phloem concentrations of sucrose. These findings suggest that in phloem feeders, sugar sensing by sugar receptors might allow tracking an increasing gradient of sucrose concentrations in the leaf, leading eventually to the location of the feeding site.

Knockdown of the Nicotinic Acetylcholine Receptor β1 Subunit Decreases the Susceptibility to Five Neonicotinoid Insecticides in Whitefly (Bemisia tabaci)

The sweet potato whitefly, Bemisia tabaci, (Gennadius) (Hemiptera:Aleyrodidae) is a global pest of crops. Neonicotinoids are efficient insecticides used for control of this pest. Insecticidal targets of neonicotinoids are insect nicotinic acetylcholine receptors (nAChRs). Here, we characterized and cloned the full length of the nAChR β1 subunit (BTβ1) in B. tabaci and confirmed the consistency of BTβ1 in B. tabaci MEAM1 and MED. Expression levels of BTβ1 in different developmental stages and body parts of adults were investigated and compared in B. tabaci MED. dsRNA was prepared to knock down BTβ1 in adult B. tabaci and significantly decreases the susceptibility to five neonicotinoid insecticides, including imidacloprid, clothianidin, thiacloprid, nitenpyram, and dinotefuran. This study indicated BTβ1 as a notable site influencing the susceptibility of B. tabaci to neonicotinoids.

A single point mutation in the Bemisia tabaci cytochrome-P450 CYP6CM1 causes enhanced resistance to neonicotinoids

The tobacco whitefly, Bemisia tabaci, is a polyphagous crop pest which causes high levels of economic damage across the globe. Insecticides are often required for the effective control of this species, among which the neonicotinoid class have been particularly widely used. Deciphering the mechanisms responsible for resistance to these chemicals is therefore critical to maintain control of B. tabaci and limit the damage it causes. An important mechanism of resistance to neonicotinoids in B. tabaci is the overexpression of the cytochrome P450 gene CYP6CM1 which leads to the enhanced detoxification of several neonicotinoids. In this study we show that qualitative changes in this P450 dramatically alter its metabolic capacity to detoxify neonicotinoids. CYP6CM1 was significantly over-expressed in two strains of B. tabaci which displayed differing levels of resistance to the neonicotinoids imidacloprid and thiamethoxam. Sequencing of the CYP6CM1 coding sequence from these strains revealed four different alleles encoding isoforms carrying several amino acid changes. Expression of these alleles in vitro and in vivo provided compelling evidence that a mutation (A387G), present in two of the CYP6CM1 alleles, results in enhanced resistance to several neonicotinoids. These data demonstrate the importance of both qualitative and quantitative changes in genes encoding detoxification enzymes in the evolution of insecticide resistance and have applied implications for resistance monitoring programs.

Tracking Adaptive Pathways of Invasive Insects: Novel Insight from Genomics

Despite the huge human and economic costs of invasive insects, which are the main group of invasive species, their environmental impacts through various mechanisms remain inadequately explained in databases and much of the invasion biology literature. High-throughput sequencing technology, especially whole-genome sequencing, has been used as a powerful method to study the mechanisms through which insects achieve invasion. In this study, we reviewed whole-genome sequencing-based advances in revealing several important invasion mechanisms of invasive insects, including (1) the rapid genetic variation and evolution of invasive populations, (2) invasion history and dispersal paths, (3) rapid adaptation to different host plant ranges, (4) strong environmental adaptation, (5) the development of insecticide resistance, and (6) the synergistic damage caused by invasive insects and endosymbiotic bacteria. We also discussed prevention and control technologies based on whole-genome sequencing and their prospects.

Sidestepping Darwin: horizontal gene transfer from plants to insects

Horizontal transfer of genetic material (HT) is the passage of DNA between organisms by means other than reproduction. Increasing numbers of HT are reported in insects, with bacteria, fungi, plants, and insects acting as the main sources of these transfers. Here, we provide a detailed account of plant-to-insect HT events. At least 14 insect species belonging to 6 orders are known to have received plant genetic material through HT. One of them, the whitefly Bemisia tabaci (Middle East Asia Minor 1), concentrates most of these transfers, with no less than 28 HT events yielding 55 plant-derived genes in this species. Several plant-to-insect HT events reported so far involve gene families known to play a role in plant-parasite interactions. We highlight methodological approaches that may further help characterize these transfers. We argue that plant-to-insect HT is likely more frequent than currently appreciated and that in-depth studies of these transfers will shed new light on plant-insect interactions.

Horizontally transferred genes as RNA interference targets for aphid and whitefly control

RNA interference (RNAi)-based technologies are starting to be commercialized as a new approach for agricultural pest control. Horizontally transferred genes (HTGs), which have been transferred into insect genomes from viruses, bacteria, fungi or plants, are attractive targets for RNAi-mediated pest control. HTGs are often unique to a specific insect family or even genus, making it unlikely that RNAi constructs targeting such genes will have negative effects on ladybugs, lacewings and other beneficial predatory insect species. In this study, we sequenced the genome of a red, tobacco-adapted isolate of Myzus persicae (green peach aphid) and bioinformatically identified 30 HTGs. We then used plant-mediated virus-induced gene silencing (VIGS) to show that several HTGs of bacterial and plant origin are important for aphid growth and/or survival. Silencing the expression of fungal-origin HTGs did not affect aphid survivorship but decreased aphid reproduction. Importantly, although there was uptake of plant-expressed RNA by Coccinella septempunctata (seven-spotted ladybugs) via the aphids that they consumed, we did not observe negative effects on ladybugs from aphid-targeted VIGS constructs. To demonstrate that this approach is more broadly applicable, we also targeted five Bemisia tabaci (whitefly) HTGs using VIGS and demonstrated that knockdown of some of these genes affected whitefly survival. As functional HTGs have been identified in the genomes of numerous pest species, we propose that these HTGs should be explored further as efficient and safe targets for control of insect pests using plant-mediated RNA interference.

A bacteriocyte symbiont determines whitefly sex ratio by regulating mitochondrial function

Nutritional symbionts influence host reproduction, but the underlying molecular mechanisms are largely unclear. We previously found that the bacteriocyte symbiont Hamiltonella impacts the sex ratio of the whitefly Bemisia tabaci. Hamiltonella synthesizes folate by cooperation with the whitefly. Folate deficiency by Hamiltonella elimination or whitefly gene silencing distorted whitefly sex ratio, and folate supplementation restored the sex ratio. Hamiltonella deficiency or gene silencing altered histone H3 lysine 9 trimethylation (H3K9me3) level, which was restored by folate supplementation. Genome-wide chromatin immunoprecipitation-seq analysis of H3K9me3 indicated mitochondrial dysfunction in symbiont-deficient whiteflies. Hamiltonella deficiency compromised mitochondrial quality of whitefly ovaries. Repressing ovary mitochondrial function led to distorted whitefly sex ratio. These findings indicate that the symbiont-derived folate regulates host histone methylation modifications, which thereby impacts ovary mitochondrial function, and finally determines host sex ratio. Our study suggests that a nutritional symbiont can regulate animal reproduction in a way that differs from reproductive manipulators.

Vitellogenin Facilitates Associations between the Whitefly and a Bacteriocyte Symbiont

Integration between animal reproduction and symbiont inheritance is fundamental in symbiosis biology, but the underlying molecular mechanisms are largely unknown. Vitellogenin (Vg) is critical for oogenesis, and it is also a pathogen pattern recognition molecule in some animals. Previous studies have shown that Vg is involved in the regulation of symbiont abundance and transmission. However, the mechanisms by which an insect and its symbiont contribute to the function of Vg and how Vg impacts the persistence of insect-microbe symbiosis remain largely unclear. Symbionts are transovarially transmitted via maternal inheritance of the bacteriocytes in the whitefly Bemisia tabaci. Surprisingly, Vg is localized in bacteriocytes of whiteflies. Vg could be synthesized in whitefly bacteriocytes by the gene Vg expressed in these cells or exported into bacteriocytes from hemolymph via the Vg receptor. We further found that the juvenile hormone and "Candidatus Portiera aleyrodidarum" (here termed Portiera) control the level and localization of Vg in whiteflies. Immunocapture PCR revealed interactions between Vg and Portiera. Suppressing Vg expression reduced Portiera abundance as well as whitefly oogenesis and fecundity. Thus, we reveal that Vg facilitated the persistence of whitefly-bacteriocyte symbiont associations. This study will provide insight into the key role of Vg in the coevolution of insect reproduction and symbiont inheritance. IMPORTANCE Intracellular heritable symbionts have been incorporated into insect reproductive and developmental biology by various mechanisms. All Bemisia tabaci species harbor the obligate symbiont Portiera in specialized insect cells called bacteriocytes. We report that the whitefly juvenile hormone and Portiera determined vitellogenin (Vg) localization in bacteriocytes of whiteflies. In turn, Vg affected whitefly fecundity as well as fitness and transmission of the symbiont. Our findings show that Vg, a multifunctional protein, is indispensable for symbiont integration into the reproduction and development of insects. This reflects the outcome of long-term coevolution of the insect-microbe symbiosis.

Subcellular Niche Segregation of Co-Obligate Symbionts in Whiteflies

Many insects contain endosymbiotic bacteria within their bodies. In multiple endosymbiotic systems comprising two or more symbionts, each of the symbionts is generally localized in a different host cell or tissue. Bemisia tabaci (Sweet potato whitefly) possesses a unique endosymbiotic system where co-obligate symbionts are localized in the same bacteriocytes. Using fluorescence in situ hybridization, we found that endosymbionts in B. tabaci MEAM1 occupy distinct subcellular habitats, or niches, within a single bacteriocyte. Hamiltonella was located adjacent to the nucleus of the bacteriocyte, while Portiera was present in the cytoplasm surrounding Hamiltonella. Immunohistochemical analysis revealed that the endoplasmic reticulum separates the two symbionts. Habitat segregation was maintained for longer durations in female bacteriocytes. The same segregation was observed in three genetically distinct B. tabaci groups (MEAM1, MED Q1, and Asia II 6) and Trialeurodes vaporariorum, which shared a common ancestor with Bemisia over 80 million years ago, even though the coexisting symbionts and the size of bacteriocytes were different. These results suggest that the habitat segregation system existed in the common ancestor and was conserved in both lineages, despite different bacterial partners coexisting with Portiera. Our findings provide insights into the evolution and maintenance of complex endosymbiotic systems and highlight the importance of organelles for the construction of separate niches for endosymbionts. IMPORTANCE Co-obligate endosymbionts in B. tabaci are exceptionally localized within the same bacteriocyte (a specialized cell for endosymbiosis), but the underlying mechanism for their coexistence remains largely unknown. This study provides evidence for niche segregation at the subcellular level between the two symbionts. We showed that the endoplasmic reticulum is a physical barrier separating the two species. Despite differences in co-obligate partners, this subcellular niche segregation was conserved across various whitefly species. The physical proximity of symbionts may enable the efficient biosynthesis of essential nutrients via shared metabolic pathways. The expression "Good fences make good neighbors" appears to be true for insect endosymbiotic systems.

What Are the Functional Roles of Piwi Proteins and piRNAs in Insects?

Research on Piwi proteins and piRNAs in insects has focused on three experimental models: oogenesis and spermatogenesis in Drosophila melanogaster, the antiviral response in Aedes mosquitoes and the molecular analysis of primary and secondary piRNA biogenesis in Bombyx mori-derived BmN4 cells. Significant unique and complementary information has been acquired and has led to a greater appreciation of the complexity of piRNA biogenesis and Piwi protein function. Studies performed in other insect species are emerging and promise to add to the current state of the art on the roles of piRNAs and Piwi proteins. Although the primary role of the piRNA pathway is genome defense against transposons, particularly in the germline, recent findings also indicate an expansion of its functions. In this review, an extensive overview is presented of the knowledge of the piRNA pathway that so far has accumulated in insects. Following a presentation of the three major models, data from other insects were also discussed. Finally, the mechanisms for the expansion of the function of the piRNA pathway from transposon control to gene regulation were considered.

Expression profile of CYP402C1 and its role in resistance to imidacloprid in the whitefly, Bemisia tabaci

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cosmopolitan insect pest causing serious damage to crop production. Cytochromes P450 (CYPs) of B. tabaci are widely known to be involved in the metabolic resistance to a variety of insecticides, continuously increasing the difficulty in controlling this pest. In this study, four P450 genes (CYP6CM1, CYP6CX1, CYP6CX3, and CYP402C1) in B. tabaci exhibited correlations with the resistance to imidacloprid. We have focused on trying to understand the function and metabolism capacity of CYP402C1. The expression profiles of CYP402C1 were examined by reverse transcription quantitative real-time PCR and fluorescence in situ hybridizations. Its role in resistance to imidacloprid was investigated by RNA interference, transgenic Drosophila melanogaster, and heterologous expression. The results showed that CYP402C1 was highly expressed in the active feeding stages of B. tabaci, such as nymphs and female adults. CYP402C1 was mainly expressed in midguts of nymphs and adults, especially in the filter chamber. Knockdown of CYP402C1 significantly decreased the resistance of B. tabaci to imidacloprid by 3.96-fold (50% lethal concentration: 186.46 versus 47.08 mg/L). Overexpression of CYP402C1 in a transgenic D. melanogaster line (Gal4 > UAS-CYP402C1) significantly increased the resistance to imidacloprid from 12.68- to 14.92-fold (129.01 and 151.80 mg/L versus 1925.14 mg/L). The heterologous expression of CYP402C1 showed a metabolism ability of imidacloprid (imidacloprid decreased by 12.51% within 2 h). This study provides new insights for CYP402C1 function in B. tabaci and will help develop new strategies in B. tabaci control and its insecticide resistance.

The redlegged earth mite draft genome provides new insights into pesticide resistance evolution and demography in its invasive Australian range

Genomic data provide valuable insights into pest management issues such as resistance evolution, historical patterns of pest invasions and ongoing population dynamics. We assembled the first reference genome for the redlegged earth mite, Halotydeus destructor (Tucker, 1925), to investigate adaptation to pesticide pressures and demography in its invasive Australian range using whole-genome pool-seq data from regionally distributed populations. Our reference genome comprises 132 autosomal contigs, with a total length of 48.90 Mb. We observed a large complex of ace genes, which has presumably evolved from a long history of organophosphate selection in H. destructor and may contribute towards organophosphate resistance through copy number variation, target-site mutations and structural variants. In the putative ancestral H. destructor ace gene, we identified three target-site mutations (G119S, A201S and F331Y) segregating in organophosphate-resistant populations. Additionally, we identified two new para sodium channel gene mutations (L925I and F1020Y) that may contribute to pyrethroid resistance. Regional structuring observed in population genomic analyses indicates that gene flow in H. destructor does not homogenize populations across large geographic distances. However, our demographic analyses were equivocal on the magnitude of gene flow; the short invasion history of H. destructor makes it difficult to distinguish scenarios of complete isolation vs. ongoing migration. Nonetheless, we identified clear signatures of reduced genetic diversity and smaller inferred effective population sizes in eastern vs. western populations, which is consistent with the stepping-stone invasion pathway of this pest in Australia. These new insights will inform development of diagnostic genetic markers of resistance, further investigation into the multifaceted organophosphate resistance mechanism and predictive modelling of resistance evolution and spread.

Adult porcine (Sus scrofa) derived inner ear cells: Characteristics in in-vitro cultures

There is a need for an animal model that closely parallels human cochlea gestational development. This study aims to document porcine inner ear anatomy, and in vitro porcine derived inner ear cell culture characteristics. Twenty-four temporal bone were harvested from 12 adult pigs (Sus scrofa). Six were formalin fixed and their maximal diameters were measured. The cochlea duct length was determined by the insertion length of a Nucleus 22 cochlear implant in two bones. Four formalin fixed bones were sectioned for histology. Cochlear and vestibular tissues were harvested from non-fixed bones, cultured and characterized at different passages (P). Gene and protein expression of multipotent stem/progenitor (Nestin and Sox2), inner ear hair (Myosin VIIa, Prestin) and supporting (Cytokeratin 18 and Vimentin) cell markers were determined. The porcine cochlea was a 3.5 turn spiral. There was a separate vestibular compartment. The cochlear mean maximal diameter and height was 7.99 and 3.77 mm, respectively. Sphere forming cells were identified on phase-contrast microscopy. The relative mRNA expression levels of KRT18, MYO7A and SLC26A5 were significantly positively correlated in cochlear cultures; and MYO7A and SLC26A5; SOX2 and KRT18; NES and SLC26A5 genes were positively correlated in vestibular cultures (p = .037, Spearman correlation [τ] = .900). Inner ear sensory and stem cell characteristics persist in passaged porcine inner ear cells. Further work is required to establish the usefulness of porcine inner ear cell cultures to the study of human inner ear disorders.

Unraveling different begomoviruses, DNA satellites and cryptic species of Bemisia tabaci and their endosymbionts in vegetable ecosystem

Bemisia tabaci species complex contains more than 46 cryptic species. It has emerged as an important pest causing significant yield loss in many cultivated crops. This pest is also a vector for more than 100 species of begomoviruses, that are a major threat for the cultivation of many crops in different regions of the world. The relation between cryptic species of the B. tabaci species complex and associated begomoviruses that infect different crops remains unclear. In the present study, four cryptic species (Asia I, China 3, Asia II 5 and Asia II-1) of B. tabaci and four associated endosymbionts (Arsenophonus, Cardinium, Rickettsia and Wolbachia) were identified in different vegetable crops. The vector-based PCR detection revealed five different begomoviruses such as okra enation leaf curl virus (OELCuV), tomato leaf curl Palampur virus (ToLCPalV), squash leaf curl China virus (SLCCNV), chilli leaf curl virus (ChiLCuV), and tomato leaf curl New Delhi virus (ToLCNDV). Of these begomoviruses, the maximum infection rate was observed (9.1%) for OELCuV, followed by 7.3% for ToLCNDV. The infection rate of the other three viruses (SLCCNV, ChiLCuV, ToLCPalV) ranged from 0.9 to 2.7% in cryptic species of B. tabaci. Further, each cryptic species was infected with multiple virus species and the virus infection rate of Asia I, Asia II-5, China 3 and Asia II-1 was 21.2%, 15.1%, 15.1% and 0.6% respectively. Similarly, in case of betasatellites the highest infection rate was 12% for ToLCBDB, followed by 6% for OLCuB and PaLCB. With regard to alphasatellites, the highest infection rate was 18.2% for AEV and 3% for CLCuMuA. This study demonstrates the distribution of cryptic species of whitefly and their endosymbionts, and associated begomoviruses and DNA satellites in vegetable ecosystem. We believe that the information generated here is useful for evolving an effective pest management strategies for vegetable production.

Silencing the gustatory receptor BtGR11 affects the sensing of sucrose in the whitefly Bemisia tabaci

RNA interference (RNAi) is powerful biotechnology for studying the in vivo functions of key genes. Based on this property, RNAi can also be used for pest control as an effective alternative to chemical pesticides. The management of phloem-sucking pests is a tricky issue in current agricultural and forestry pest control. RNAi can silence key chemoreceptor genes of phloem-sucking pests; thereby regulating the behavior of these pests can be manipulated. So, it is considered to be a promising new type of ecological pest management strategy. In this study, we identified a candidate taste receptor gene, BtGR11, that controls the taste sensitivity to sucrose in the whitefly Bemisia tabaci, which is a serious invasive phloem-sucking pest worldwide. Functional analyses using the Xenopus oocyte expression system and the two-electrode voltage-clamp system revealed that the oocytes expressing BtGR11 responded to sucrose. Furthermore, we found that silencing BtGR11 by RNAi inhibited the function of sensing sucrose in the whitefly. This study reports a key chemoreceptor gene that can be used for the understanding of the gustatory sensing mechanisms of whitefly to deterrent.

Coevolution of Metabolic Pathways in Blattodea and Their Blattabacterium Endosymbionts, and Comparisons with Other Insect-Bacteria Symbioses

Many insects harbor bacterial endosymbionts that supply essential nutrients and enable their hosts to thrive on a nutritionally unbalanced diet. Comparisons of the genomes of endosymbionts and their insect hosts have revealed multiple cases of mutually-dependent metabolic pathways that require enzymes encoded in 2 genomes. Complementation of metabolic reactions at the pathway level has been described for hosts feeding on unbalanced diets, such as plant sap. However, the level of collaboration between symbionts and hosts that feed on more variable diets is largely unknown. In this study, we investigated amino acid and vitamin/cofactor biosynthetic pathways in Blattodea, which comprises cockroaches and termites, and their obligate endosymbiont Blattabacterium cuenoti (hereafter Blattabacterium). In contrast to other obligate symbiotic systems, we found no clear evidence of "collaborative pathways" for amino acid biosynthesis in the genomes of these taxa, with the exception of collaborative arginine biosynthesis in 2 taxa, Cryptocercus punctulatus and Mastotermes darwiniensis. Nevertheless, we found that several gaps specific to Blattabacterium in the folate biosynthetic pathway are likely to be complemented by their host. Comparisons with other insects revealed that, with the exception of the arginine biosynthetic pathway, collaborative pathways for essential amino acids are only observed in phloem-sap feeders. These results suggest that the host diet is an important driving factor of metabolic pathway evolution in obligate symbiotic systems. IMPORTANCE The long-term coevolution between insects and their obligate endosymbionts is accompanied by increasing levels of genome integration, sometimes to the point that metabolic pathways require enzymes encoded in two genomes, which we refer to as "collaborative pathways". To date, collaborative pathways have only been reported from sap-feeding insects. Here, we examined metabolic interactions between cockroaches, a group of detritivorous insects, and their obligate endosymbiont, Blattabacterium, and only found evidence of collaborative pathways for arginine biosynthesis. The rarity of collaborative pathways in cockroaches and Blattabacterium contrasts with their prevalence in insect hosts feeding on phloem-sap. Our results suggest that host diet is a factor affecting metabolic integration in obligate symbiotic systems.

A balance between vector survival and virus transmission is achieved through JAK/STAT signaling inhibition by a plant virus

Viruses pose a great threat to animal and plant health worldwide, with many being dependent on insect vectors for transmission between hosts. While the virus-host arms race has been well established, how viruses and insect vectors adapt to each other remains poorly understood. Begomoviruses comprise the largest genus of plant-infecting DNA viruses and are exclusively transmitted by the whitefly Bemisia tabaci. Here, we show that the vector Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway plays an important role in mediating the adaptation between the begomovirus tomato yellow leaf curl virus (TYLCV) and whiteflies. We found that the JAK/STAT pathway in B. tabaci functions as an antiviral mechanism against TYLCV infection in whiteflies as evidenced by the increase in viral DNA and coat protein (CP) levels after inhibiting JAK/STAT signaling. Two STAT-activated effector genes, BtCD109-2 and BtCD109-3, mediate this anti-TYLCV activity. To counteract this vector immunity, TYLCV has evolved strategies that impair the whitefly JAK/STAT pathway. Infection of TYLCV is associated with a reduction of JAK/STAT pathway activity in whiteflies. Moreover, TYLCV CP binds to STAT and blocks its nuclear translocation, thus, abrogating the STAT-dependent transactivation of target genes. We further show that inhibition of the whitefly JAK/STAT pathway facilitates TYLCV transmission but reduces whitefly survival and fecundity, indicating that this JAK/STAT-dependent TYLCV-whitefly interaction plays an important role in keeping a balance between whitefly fitness and TYLCV transmission. This study reveals a mechanism of plant virus-insect vector coadaptation in relation to vector survival and virus transmission.

A reproducible and sensitive method for generating high-quality transcriptomes from single whitefly salivary glands and other low-input tissues

Transcriptomic studies are an important tool for understanding the molecular pathways underlying host plant use by agricultural pests, including vectors of damaging plant pathogens. Thus far, bulk RNA-Seq has been the main approach for non-model insects. This method relies on pooling large numbers of whole organisms or hundreds of individually dissected organs. The latter approach is logistically challenging, may introduce artifacts of handling and storage, and is not compatible with biological replication. Here, we tested an approach to generate transcriptomes of individual salivary glands and other low-input body tissues from whiteflies (Bemisia tabaci MEAM1), which are major vectors of plant viruses. By comparing our outputs to published bulk RNA-Seq datasets for whole whitefly bodies and pools of salivary glands, we demonstrate that this approach recovers similar numbers of transcripts relative to bulk RNA-Seq in a tissue-specific manner, and for some metrics, exceeds performance of bulk tissue RNA-Seq. Libraries generated from individual salivary glands also yielded additional novel transcripts not identified in pooled salivary gland datasets, and had hundreds of enriched transcripts when compared with whole head tissues. Overall, our study demonstrates that it is feasible to produce high quality, replicated transcriptomes of whitefly salivary glands and other low-input tissues. We anticipate that our approach will expand hypothesis-driven research on salivary glands of whiteflies and other Hemiptera, thus enabling novel control strategies to disrupt feeding and virus transmission.

Evolved transcriptional responses and their trade-offs after long-term adaptation of Bemisia tabaci to a marginally-suitable host

Although generalist insect herbivores can migrate and rapidly adapt to a broad range of host plants, they can face significant difficulties when accidentally migrating to novel and marginally-suitable hosts. What happens, both in performance and gene expression regulation, if these marginally-suitable hosts must be used for multiple generations before migration to a suitable host can take place, largely remains unknown. In this study, we established multigenerational colonies of the whitefly Bemisia tabaci, a generalist phloem-feeding species, adapted to a marginally-suitable host (habanero pepper) or an optimal host (cotton). We used reciprocal host tests to estimate the differences in performance of the populations on both hosts under optimal (30 oC) and mild-stressful (24 oC) temperature conditions, and documented the associated transcriptomic changes. The habanero pepper-adapted population greatly improved its performance on habanero pepper but did not reach its performance level on cotton, the original host. It also showed reduced performance on cotton, relative to the non-adapted population, and an antagonistic effect of the lower-temperature stressor. The transcriptomic data revealed that most of the expression changes, associated with long-term adaptation to habanero pepper, can be categorized as "evolved" with no initial plastic response. Three molecular functions dominated: enhanced formation of cuticle structural constituents, enhanced activity of oxidation-reduction processes involved in neutralization of phytotoxins and reduced production of proteins from the cathepsin B family. Taken together, these findings indicate that generalist insects can adapt to novel host plants by modifying the expression of a relatively small set of specific molecular functions.

The Unfolded-Protein Response Triggers the Arthropod Immune Deficiency Pathway

The insect immune deficiency (IMD) pathway is a defense mechanism that senses and responds to Gram-negative bacteria. Ticks lack genes encoding upstream components that initiate the IMD pathway. Despite this deficiency, core signaling molecules are present and functionally restrict tick-borne pathogens. The molecular events preceding activation remain undefined. Here, we show that the unfolded-protein response (UPR) initiates the IMD network. The endoplasmic reticulum (ER) stress receptor IRE1α is phosphorylated in response to tick-borne bacteria but does not splice the mRNA encoding XBP1. Instead, through protein modeling and reciprocal pulldowns, we show that Ixodes IRE1α complexes with TRAF2. Disrupting IRE1α-TRAF2 signaling blocks IMD pathway activation and diminishes the production of reactive oxygen species. Through in vitro, in vivo, and ex vivo techniques, we demonstrate that the UPR-IMD pathway circuitry limits the Lyme disease-causing spirochete Borrelia burgdorferi and the rickettsial agents Anaplasma phagocytophilum and A. marginale (anaplasmosis). Altogether, our study uncovers a novel linkage between the UPR and the IMD pathway in arthropods. IMPORTANCE The ability of an arthropod to harbor and transmit pathogens is termed "vector competency." Many factors influence vector competency, including how arthropod immune processes respond to the microbe. Divergences in innate immunity between arthropods are increasingly being reported. For instance, although ticks lack genes encoding key upstream molecules of the immune deficiency (IMD) pathway, it is still functional and restricts causative agents of Lyme disease (Borrelia burgdorferi) and anaplasmosis (Anaplasma phagocytophilum). How the IMD pathway is activated in ticks without classically defined pathway initiators is not known. Here, we found that a cellular stress response network, the unfolded-protein response (UPR), functions upstream to induce the IMD pathway and restrict transmissible pathogens. Collectively, this explains how the IMD pathway can be activated in the absence of canonical pathway initiators. Given that the UPR is highly conserved, UPR-initiated immunity may be a fundamental principle impacting vector competency across arthropods.

Differential Transcriptional Responses in Two Old World Bemisia tabaci Cryptic Species Post Acquisition of Old and New World Begomoviruses

Begomoviruses are transmitted by several cryptic species of the sweetpotato whitefly, Bemisia tabaci (Gennadius), in a persistent and circulative manner. Upon virus acquisition and circulative translocation within the whitefly, a multitude of molecular interactions occur. This study investigated the differentially expressed transcript profiles associated with the acquisition of the Old World monopartite begomovirus, tomato yellow leaf curl virus (TYLCV), and two New World bipartite begomoviruses, sida golden mosaic virus (SiGMV) and cucurbit leaf crumple virus (CuLCrV), in two invasive B. tabaci cryptic species, Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED). A total of 881 and 559 genes were differentially expressed in viruliferous MEAM1 and MED whiteflies, respectively, compared with their non-viruliferous counterparts, of which 146 genes were common between the two cryptic species. For both cryptic species, the number of differentially expressed genes (DEGs) associated with TYLCV and SiGMV acquisition were higher compared with DEGs associated with CuLCrV acquisition. Pathway analysis indicated that the acquisition of begomoviruses induced differential changes in pathways associated with metabolism and organismal systems. Contrasting expression patterns of major genes associated with virus infection and immune systems were observed. These genes were generally overexpressed and underexpressed in B. tabaci MEAM1 and MED adults, respectively. Further, no specific expression pattern was observed among genes associated with fitness (egg production, spermatogenesis, and aging) in viruliferous whiteflies. The weighted gene correlation network analysis of viruliferous B. tabaci MEAM1 and MED adults identified different hub genes potentially implicated in the vector competence and circulative tropism of viruses. Taken together, the results indicate that both vector cryptic species and the acquired virus species could differentially affect gene expression.

Pervasive Endosymbiont Arsenophonus Plays a Key Role in the Transmission of Cotton Leaf Curl Virus Vectored by Asia II-1 Genetic Group of Bemisia tabaci

Insects often coevolved with their mutualistic partners such as gut endosymbionts, which play a key in the physiology of host. Studies on such interactions between Bemisia tabaci and its primary and secondary endosymbionts have gained importance due to their indispensable roles in the biology of this insect. Present study reports the predominance of two secondary endosymbionts, Arsenophonus and Cardinium in the Asia II-1 genetic group of whitefly and elucidates their role in the transmission of its vectored Cotton leaf curl virus. Selective elimination of endosymbionts was optimized using serial concentration of ampicillin, chloramphenicol, kanamycin, tetracycline, and rifampicin administered to viruliferous whiteflies through sucrose diet. Primary endosymbiont, Portiera was unresponsive to all the antibiotics, however, rifampicin and tetracycline at 90 μg/ml selectively eliminated Arsenophonus from the whitefly. Elimination of Arsenophonus resulted in significant decrease in virus titer from viruliferous whitefly, further the CLCuV transmission efficiency of these whiteflies was significantly reduced compared to the control flies. Secondary endosymbiont, Cardinium could not be eliminated completely even with higher concentrations of antibiotics. Based on the findings, Arsenophonus plays a key role in the retention and transmission of CLCuV in the Asia II-1 genetic group of B. tabaci, while the role of Cardinium could not be established due to its unresponsiveness to antibiotics.

The Adipokinetic Peptides of Hemiptera: Structure, Function, and Evolutionary Trends

The Hemiptera comprise the most species-rich order of the hemimetabolous insects. Members of a number of superfamilies, most notably especially the more basal ones such as white flies, psyllids and aphids, belong to the most destructive agricultural insects known worldwide. At the other end of the phylogenetic tree are hemipterans that are notorious medical pests (e.g. kissing bugs). Most of the hemipteran species are good flyers, and lipid oxidation plays a pivotal role to power the contraction of flight muscles and, in aquatic water bugs, also deliver the ATP for the extensive swimming action of the leg muscles. Mobilization of stored lipids (mostly triacylglycerols in the fat body) to circulating diacylglycerols in the hemolymph is regulated by a set of small neuropeptides, the adipokinetic hormones (AKHs). We searched the literature and publicly available databases of transcriptomes and genomes to present here AKH sequences from 191 hemipteran species. Only few of these peptides were sequenced via Edman degradation or mass spectrometry, and even fewer were characterized with molecular biology methods; thus, the majority of the AKHs we have identified by bioinformatics are merely predicted sequences at this stage. Nonetheless, a total of 42 AKH primary sequences are assigned to Hemiptera. About 50% of these structures occur also in other insect orders, while the remaining 50% are currently unique for Hemiptera. We find 9 novel AKHs not shown to be synthesized before in any insect. Most of the hemipteran AKHs are octapeptides (28) but there is an impressive number of decapeptides (12) compared to other speciose orders such as Diptera and Lepidoptera. We attempt to construct a hypothetical molecular peptide evolution of hemipteran AKHs and find quite a bit of overlapping with current phylogenetic ideas of the Hemiptera. Lastly, we discuss the possibility to use the sequence of the aphid AKH as lead peptide for the research into a peptide mimetic fulfilling criteria of a green insecticide.

Characterization of Chromatin Remodeling Genes Involved in Thermal Tolerance of Biologically Invasive Bemisia tabaci

As an invasive species, Bemisia tabaci Mediterranean (MED) has notable potential to adapt to a wide range of environmental temperatures, which enables it to successfully spread after invasion and occupy habitats over a wide latitude range. It has been postulated that chromatin remodeling mechanisms are related to the rapid acquisition of adaptive traits and thermal resistance in invasive species; however, relevant experimental evidence is scarce. To identify the molecular characteristics and assess the role of chromatin remodelers in thermal stress within invasive MED and native Asia II 1 of the B. tabaci species complex, we identified 13 switching defective/sucrose non-fermenting (SWI/SNF) and 10 imitation switch (ISWI) family members in the B. tabaci genome, analyzed their molecular characteristics and structures, and identified key mutation sites between MED and Asia II 1, then cloned the catalytic subunits, and revealed the difference in thermal tolerance function. The results showed that the expression levels of Bt-BRM-1 and Bt-BRM-2 were significantly higher in MED than in Asia II 1 during heat stress, and Bt-BRM-2 expression was significantly higher during cold stress. In addition, RNA interference results indicated that the two target genes had similar temperature tolerance function in the both two cryptic species. This study is the first to identify and analyze the molecular characteristics of SWI/SNF and ISWI family members and reveal their potential key roles in temperature tolerance in poikilothermic ectotherms. The results will assist in understanding the underlying temperature adaptation mechanism of invasive insects and will enrich stress adaptation research systems from an epigenetic perspective.

Transcriptomic Changes of Bemisia tabaci Asia II 1 Induced by Chilli Leaf Curl Virus Trigger Infection and Circulation in Its Vector

Bemisia tabaci (Hemiptera: Aleyrodidae) is a highly efficient vector in the spread of chilli leaf curl virus (ChiLCV, Begomovirus) which is a major constraint in the production of chilli in South Asia. Transcriptome analysis of B. tabaci post-6 h acquisition of ChiLCV showed differential expression of 80 (29 upregulated and 51 downregulated) genes. The maximum number of DEGs are categorized under the biological processes category followed by cellular components and molecular functions. KEGG analysis of DEGs showed that the genes are involved in the functions like metabolism, signaling pathways, cellular processes, and organismal systems. The expression of highly expressed 20 genes post-ChiLCV acquisition was validated in RT-qPCR. DEGs such as cytosolic carboxypeptidase 3, dual-specificity protein phosphatase 10, 15, dynein axonemal heavy chain 17, fasciclin 2, inhibin beta chain, replication factor A protein 1, and Tob1 were found enriched and favored the virus infection and circulation in B. tabaci. The present study provides an improved understanding of the networks of molecular interactions between B. tabaci and ChiLCV. The candidate genes of B. tabaci involved in ChiLCV transmission would be novel targets for the management of the B. tabaci-begomovirus complex.

New insights into plant natriuretic peptide evolution: From the lysogenic conversion in Xanthomonas to the lateral transfer to the whitefly Bemisia tabaci

Plant natriuretic peptide-like (PNP) are signaling molecules related to adaptive responses to stress. The Arabidopsis thaliana PNP (AtPNP-A) is capable of modulating catalase 2 (CAT2) and rubisco activase (RCA) activity in some circumstances. Interestingly, many plant-pathogens co-opted PNP-like molecules to their benefit. For instance, the citrus pathogen Xanthomonas citri carries a PNP-like (XacPNP) that can mimic and regulate plant homeostasis, and many phytopathogenic fungi carry effectors (e.g., Ave1 and AvrLm6) that are indeed PNP-like homologs. This work investigates the PNP-like evolution across the tree of life, revealing many parallel gains and duplications in plant and fungi kingdoms. All PNP-like proteins in the final dataset are structurally similar, containing the AtPNP-A active domains modulating CAT2 activity and RCA interaction. Comparative genomics evinced that XacPNP is a lysogenic conversion factor associated with a Myoviridae-like prophage identified in many Xanthomonas species. Surprisingly, a PNP-like homolog was identified in Bemisia tabaci, an important agricultural pest, being to date the second example of lateral gene transfer (LGT) from plant to the whitefly. Moreover, the Bemisia PNP-like homolog can also be considered a potential new effector of this phloem-feeding insect. Noteworthy, the whiteflies infest many plants carrying PNP-like copies and interact with some of their bacterial and fungal pathogens, strongly suggesting complex recipient/donor traits of PNP by LGT and bringing new insights into the evolution of host-pathogen arms race across the tree of life.