Retrotransposon-mediated evolutionary rewiring of a pathogen response orchestrates a resistance phenotype in an insect host

Throwing Brazilian strains into the melting pot of P. xylostella resistance to Bacillus thuringiensis

The resistance of pest insects to biopesticides based on the bacterium Bacillus thuringiensis (Bt) is normally associated with changes to the receptors involved in the mechanism of action of the pesticidal proteins produced by Bt. In some strains of Plutella xylostella (the diamondback moth) resistance has evolved through a signalling mechanism in which the genes encoding the receptor proteins are downregulated whereas in others it has been linked to structural changes in the receptors themselves. One such well characterized mutation is in the ABCC2 gene indicating that changes to this protein can result in resistance. However other studies have found that knocking out this protein does not result in a significant level of resistance. In this study we wanted to test the hypothesis that constitutive receptor downregulation is the major cause of Bt resistance in P. xylostella and that mutations in the now poorly expressed receptor genes may not contribute significantly to the phenotype. To that end we investigated the expression of a receptor (ABCC2) and the major regulator of the signalling pathway (MAP4K4) in two resistant and four susceptible strains. No correlation was found between expression levels and susceptibility; however, a frameshift mutation was identified in the ABCC2 receptor in a newly characterized resistant strain.

The role of ATP-binding cassette transporters in arthropod pesticide toxicity and resistance

Pesticide resistance in arthropods threatens agricultural productivity and the control of vector-borne diseases. The ATP-binding cassette (ABC) transporters have emerged as important factors in the toxicity of synthetic pesticides, as well as for Bacillus thuringiensis insecticidal Cry protein binding. Depending on the localization of expression, both higher and lower expression of ABCs have been linked with pesticide resistance. The recent development of genetic-based approaches such as RNAi and CRISPR/Cas9 gene editing in nonmodel species, has greatly contributed to unveil their functional importance in pesticide toxicity and resistance. Using these tools, we are now poised to further unravel the molecular genetic mechanisms of gene regulation uncovering more elusive regulatory resistance genes.

Characterization and functional analysis of UDP-glycosyltransferases reveal their contribution to phytochemical flavone tolerance in Spodoptera litura

Efficient detoxification is the key factor for phytophagous insect to adapt to phytochemicals. However, the role of uridine diphosphate (UDP)-glycosyltransferases (UGTs) in insect anti-defense to phytochemical flavone is largely unknown. In this study, 52 UGT genes were identified in Spodoptera litura and they presented evident gene duplication. UGT played a crucial part in larval tolerance to flavone because the enzyme activity and transcriptional level of 77 % UGT members were remarkably upregulated by flavone administration and suppression of UGT enzyme activity and gene expressions significantly increased larval susceptibility to flavone. Bacteria coexpressing UGTs had high survival rates under flavone treatment and flavone was dramatically metabolized by UGT recombinant cells, which indicated the involvement of UGTs in flavone detoxification. What's more, ecdysone pathway was activated by flavone. Topical application of 20-hydroxyecdysone highly upregulated UGT enzyme activity and more than half of UGT expressions. The effects were opposite when ecdysone receptor (EcR) and ultraspiracle (USP)-mediated ecdysone signaling pathway was inhibited. Furtherly, promoter reporter assays of 5 UGT genes showed that their transcription activities were notably increased by cotransfection with EcR and USP. In consequence, this study suggested that UGTs were involved in flavone detoxification and their transcriptional expressions were regulated by ecdysone pathway.

Multidrug resistance of Botrytis cinerea associated with its adaptation to plant secondary metabolites

Fungicides are an effective way to control gray mold of grapes, but the pathogen Botrytis cinerea can develop resistance, overcoming the effectiveness of a fungicide that is repeatedly applied. More importantly, the emergence of multidrug resistance (MDR) in the field, where multiple fungicides with different modes of action simultaneously lose their efficacies, is a significant concern. MDR is associated with ATP-binding cassette (ABC) transporters of the pathogen, and certain plant secondary metabolites (PSMs) stimulate the upregulation of ABC transporters, we hypothesized that the pathogen's preadaptation to PSMs might contribute to MDR development. To test this in B. cinerea, ten PSMs, namely, resveratrol, reserpine, chalcone, flavanone, eugenol, farnesol, anethene, camptothecin, salicylic acid, and psoralen, were selected based on their association with ABC transporters involved in fungicide resistance. B. cinerea strain B05.10 was continuously transferred for 15 generations on potato dextrose agar amended with a PSM (PDAP), and sensitivities to PSMs and fungicides were examined on the 5th, 10th, and 15th generations. RNA was extracted from B. cinerea from the selected generations. After 15 generations of culture transfers, an up-regulation was observed in the expression of ABC transporter-encoding genes BcatrB, BcatrD, and BcatrK using quantitative polymerase chain reaction (qPCR). This upregulation was found to contribute to MDR of B. cinerea against two or more fungicides, among azoxystrobin, boscalid, fludioxonil, difenoconazole, prochloraz, and pyrimethanil. This finding was confirmed through genetic transformation. The decreased sensitivity of B. cinerea to fungicides was confirmed as a subsequent MDR phenotype after exposure to camptothecin, flavanone, and resveratrol. Besides, transcriptome analysis also revealed the upregulation of transcription factors related to ABC expression following resveratrol exposure. This suggests that PSMs contributed to inducing preadaptation of B. cinerea, leading to subsequent MDR.IMPORTANCEThe emergence of MDR in plant pathogens is a threat to plant disease management and leads to the use of excessive fungicides. Botrytis cinerea is of particular concern because its MDR has widely emerged in the field. Understanding its genesis is the first step for controlling MDR. In this study, the contribution of PSMs to MDR has been examined. Effective management of this pathogen in agroecosystems relies on a better understanding of how it copes with phytochemicals or fungicides.

RNA m6 A Methylation Suppresses Insect Juvenile Hormone Degradation to Minimize Fitness Costs in Response to A Pathogenic Attack

Bioinsecticides and transgenic crops based on the bacterial pathogen Bacillus thuringiensis (Bt) can effectively control diverse agricultural insect pests, nevertheless, the evolution of resistance without obvious fitness costs has seriously eroded the sustainable use of these Bt products. Recently, it has been discovered that an increased titer of juvenile hormone (JH) favors an insect host (Plutella xylostella) to enhance fitness whilst resisting the Bt pathogen, however, the underlying regulatory mechanisms of the increased JH titer are obscure. Here, the involvement of N6 -methyladenosine (m6 A) RNA modification in modulating the availability of JH in this process is defined. Specifically, it is found that two m6 A methyltransferase subunit genes, PxMettl3 and PxMettl14, repress the expression of a key JH-degrading enzyme JH esterase (JHE) to induce an increased JH titer, mitigating the fitness costs associated with a robust defense against the Bt pathogen. This study identifies an as-yet uncharacterized m6 A-mediated epigenetic regulator of insect hormones for maintaining fitness during pathogen defense and unveils an emerging Bt resistance-related m6 A methylation atlas in insects, which further expands the functional landscape of m6 A modification and showcases the pivotal role of epigenetic regulation in host-pathogen interactions.

The C2H2 zinc finger transcription factor CF2-II regulates multi-insecticide resistance-related gut-predominant ABC transporters in Aphis gossypii Glover

Clarifying the molecular mechanisms of cotton aphid resistance to various insecticides is crucial for the long-term safe application of insecticides in chemical control. ATP-binding cassette (ABC) transporters mediate the membrane transport of various substrates (including exogenous substances). Experiments confirmed that ABCB5, ABCF2, and MRP12 contributed to high levels of resistance to spirotetramat, cyantraniliprole, thiamethoxam or imidacloprid. Binding sites of the C2H2 zinc finger transcription factor CF2-II was predicted to be located in the promoters of ABCB5, ABCF2, and MRP12. The expression levels of ABCB5, ABCF2, and MRP12 were significantly upregulated after silencing CF2-II. The results of dual-luciferase reporter assays demonstrated a negative regulatory relationship between CF2-II and ABC transporter promoters. Furthermore, yeast one-hybrid (Y1H) and electrophoresis mobility shift assays (EMSAs) revealed that CF2-II inhibited the expression of ABC transporter genes through interaction with binding sites [ABCF2.p (-1149/-1140) or MRP12.p (-1189/-1181)]. The above results indicated that ABCB5, ABCF2, and MRP12 were negatively regulated by the transcription factor CF2-II, which will help us further understand the mechanism of transcriptional adaption of multi-insecticides resistant related ABC transporters in response to xenobiotics.

Downregulation of a transcription factor associated with resistance to Bt toxin Vip3Aa in the invasive fall armyworm

Transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) have revolutionized control of some major pests. However, more than 25 cases of field-evolved practical resistance have reduced the efficacy of transgenic crops producing crystalline (Cry) Bt proteins, spurring adoption of alternatives including crops producing the Bt vegetative insecticidal protein Vip3Aa. Although practical resistance to Vip3Aa has not been reported yet, better understanding of the genetic basis of resistance to Vip3Aa is urgently needed to proactively monitor, delay, and counter pest resistance. This is especially important for fall armyworm (Spodoptera frugiperda), which has evolved practical resistance to Cry proteins and is one of the world's most damaging pests. Here, we report the identification of an association between downregulation of the transcription factor gene SfMyb and resistance to Vip3Aa in S. frugiperda. Results from a genome-wide association study, fine-scale mapping, and RNA-Seq identified this gene as a compelling candidate for contributing to the 206-fold resistance to Vip3Aa in a laboratory-selected strain. Experimental reduction of SfMyb expression in a susceptible strain using RNA interference (RNAi) or CRISPR/Cas9 gene editing decreased susceptibility to Vip3Aa, confirming that reduced expression of this gene can cause resistance to Vip3Aa. Relative to the wild-type promoter for SfMyb, the promoter in the resistant strain has deletions and lower activity. Data from yeast one-hybrid assays, genomics, RNA-Seq, RNAi, and proteomics identified genes that are strong candidates for mediating the effects of SfMyb on Vip3Aa resistance. The results reported here may facilitate progress in understanding and managing pest resistance to Vip3Aa.

Enthralling genetic regulatory mechanisms meddling insecticide resistance development in insects: role of transcriptional and post-transcriptional events

Insecticide resistance in insects severely threatens both human health and agriculture, making insecticides less compelling and valuable, leading to frequent pest management failures, rising input costs, lowering crop yields, and disastrous public health. Insecticide resistance results from multiple factors, mainly indiscriminate insecticide usage and mounted selection pressure on insect populations. Insects respond to insecticide stress at the cellular level by modest yet significant genetic propagations. Transcriptional, co-transcriptional, and post-transcriptional regulatory signals of cells in organisms regulate the intricate processes in gene expressions churning the genetic information in transcriptional units into proteins and non-coding transcripts. Upregulation of detoxification enzymes, notably cytochrome P450s (CYPs), glutathione S-transferases (GSTs), esterases [carboxyl choline esterase (CCE), carboxyl esterase (CarE)] and ATP Binding Cassettes (ABC) at the transcriptional level, modification of target sites, decreased penetration, or higher excretion of insecticides are the noted insect physiological responses. The transcriptional regulatory pathways such as AhR/ARNT, Nuclear receptors, CncC/Keap1, MAPK/CREB, and GPCR/cAMP/PKA were found to regulate the detoxification genes at the transcriptional level. Post-transcriptional changes of non-coding RNAs (ncRNAs) such as microRNAs (miRNA), long non-coding RNAs (lncRNA), and epitranscriptomics, including RNA methylation, are reported in resistant insects. Additionally, genetic modifications such as mutations in the target sites and copy number variations (CNV) are also influencing insecticide resistance. Therefore, these cellular intricacies may decrease insecticide sensitivity, altering the concentrations or activities of proteins involved in insecticide interactions or detoxification. The cellular episodes at the transcriptional and post-transcriptional levels pertinent to insecticide resistance responses in insects are extensively covered in this review. An overview of molecular mechanisms underlying these biological rhythms allows for developing alternative pest control methods to focus on insect vulnerabilities, employing reverse genetics approaches like RNA interference (RNAi) technology to silence particular resistance-related genes for sustained insect management.

Assessment of the role of an ABCC transporter TuMRP1 in the toxicity of abamectin to Tetranychus urticae

The rapid evolution of pest resistance threatens the sustainable utilization of bioinsecticides such as abamectin, and so deciphering the molecular mechanisms affecting toxicity and resistance is essential for their long-term application. Historical studies of abamectin resistance in arthropods have mainly focused on mechanisms involving the glutamate-gated chloride channel (GluCl) targets, with the role of metabolic processes less clear. The two-spotted spider mite, Tetranychus urticae, is a generalist herbivore notorious for rapidly developing resistance to pesticides worldwide, and abamectin has been widely used for its control in the field. After reanalyzing previous transcriptome and RNA-seq data, we here identified an ABC transporter subfamily C gene in T. urticae named multidrug resistance-associated protein 1 (TuMRP1), whose expression differed between susceptible and resistant populations. Synergism bioassays with the inhibitor MK-571, the existence of a genetic association between TuMRP1 expression and susceptibility to abamectin, and the effect of RNA interference mediated silencing of TuMRP1 were all consistent with a direct role of this transporter protein in the toxicity of abamectin. Although ABC transporters are often involved in removing insecticidal compounds from cells, our data suggest either an alternative role for these proteins in the mechanism of action of abamectin or highlight an indirect association between their expression and abamectin toxicity.

A Comprehensive Review on the Roles of Metals Mediating Insect-Microbial Pathogen Interactions

Insects and microbial pathogens are ubiquitous and play significant roles in various biological processes, while microbial pathogens are microscopic organisms that can cause diseases in multiple hosts. Insects and microbial pathogens engage in diverse interactions, leveraging each other's presence. Metals are crucial in shaping these interactions between insects and microbial pathogens. However, metals such as Fe, Cu, Zn, Co, Mo, and Ni are integral to various physiological processes in insects, including immune function and resistance against pathogens. Insects have evolved multiple mechanisms to take up, transport, and regulate metal concentrations to fight against pathogenic microbes and act as a vector to transport microbial pathogens to plants and cause various plant diseases. Hence, it is paramount to inhibit insect-microbe interaction to control pathogen transfer from one plant to another or carry pathogens from other sources. This review aims to succinate the role of metals in the interactions between insects and microbial pathogens. It summarizes the significance of metals in the physiology, immune response, and competition for metals between insects, microbial pathogens, and plants. The scope of this review covers these imperative metals and their acquisition, storage, and regulation mechanisms in insect and microbial pathogens. The paper will discuss various scientific studies and sources, including molecular and biochemical studies and genetic and genomic analysis.