Bt Cry1Ac Research Articles

Inheritance and ecological effects of exogenous genes from transgenic Brassica napus to Brassica juncea hybrids

●With the rapid development of new breeding techniques, the ecological impacts of transgenic plants receive wide concern again, particularly for potential gene flow from transgenic crops to their relatives. The transgene insertion position, number of gene copies, and flanking sequence of exogenous genes integrated into the recipient genome affect the genetic stability and fitness of offspring.●We employed hybrids F1 and F2, six backcross generations BC1-BC6 and BC1F1 from transgenic Brassica napus with Bacillus thuringiensis (Bt) cry1Ac gene and its wild relative B. juncea through hand pollination. We detected exogenous gene copies, mRNA transcription, and protein expression by ddPCR, qRT-PCR and ELISA, and the fitness of hybrid and backcross generations.●Exogenous genes followed Mendelian segregation expectations in hybrid and backcrossed generations, with stable gene copies, mRNA transcription and protein concentration of exogenous genes in offspring. Exogenous gene copies had no significant effects on plant fitness, but had positive effects on mRNA transcription and protein concentration that varied with growth stages in hybrid and backcross generations.●Our study demonstrated inheritance and ecological effects of exogenous genes from transgenic plants to wild relatives, which will help ecological risk management of biotechnological plants released in the nature.

Differential susceptibility of Spodoptera frugiperda (Lepidoptera: Noctuidae) to single versus pyramided Bt traits in Brazilian soybean: what doesn't kill you makes you stronger?

Lepidopteran pest control in agriculture has become heavily dependent on cultivars that express Bacillus thuringiensis (Bt) toxins as 'plant-incorporated protectants'. However, populations of Spodoptera frugiperda (Smith) in Brazil appear resistant to the Bt traits currently available in commercial soybean cultivars. This study evaluated S. frugiperda life history when feeding on three different Bt soybean cultivars. Cultivars expressing Cry1Ac + Cry1F and Cry1A.105 + Cry2Ab2 + Cry1Ac Bt toxins caused 100% larval mortality in S. frugiperda. Both non-Bt and Cry1Ac-expressing soybean induced transgenerational effects that increased the survival of subsequent generations. A Cry1Ac soybean diet reduced the generation time (T) of S. frugiperda relative to non-Bt soybean, resulting in shorter generation time and more rapid population growth. The implications of these results revealed how diet can alter aspects of insect life history and biology, and have important implications for sustainable management of S. frugiperda on soybean. © 2024 Society of Chemical Industry.

Rational design and application of broad-spectrum antibodies for Bt Cry toxins determination

Using the amino acid sequences and analysis of selected known structures of Bt Cry toxins, Cry1Ab, Cry1Ac, Cry1Ah, Cry1B, Cry1C and Cry1F we specifically designed immunogens. After antibodies selection, broad-spectrum polyclonal antibodies (pAbs) and monoclonal antibody (namely 1A0-mAb) were obtained from rabbit and mouse, respectively. The produced pAbs displayed broad spectrum activity by recognizing Cry1 toxin, Cry2Aa, Cry2Ab and Cry3Aa with half maximal inhibitory concentration (IC50) values of 0.12–9.86 μg/mL. Similarly, 1A0-mAb showed broad spectrum activity, recognizing all of the above Cry protein (IC50 values of 4.66–20.46 μg/mL) with the exception of Cry2Aa. Using optimizations studies, 1A10-mAb was used as a capture antibody and pAbs as detection antibody. Double antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISAs) were established for Cry1 toxin, Cry2Ab and Cry3Aa with the limit of detection (LOD) values of 2.36–36.37 ng/mL, respectively. The present DAS-ELISAs had good accuracy and precisions for the determination of Cry toxin spiked tap water, corn, rice, soybeans and soil samples. In conclusion, the present study has successfully obtained broad-spectrum pAbs and mAb. Furthermore, the generated pAbs- and mAb-based DAS-ELISAs protocol can potentially be used for the broad-spectrum monitoring of eight common subtypes of Bt Cry toxins residues in food and environmental samples.

Cry Toxins from <i>Bt</i> Bollgard II® Cotton Seeds: An Affordable Source for Insect Bioassays

The relative expression of Bacillus thuringiensis (Bt) Cry1Ac and Cry2Ab toxins from seeds of Bt Bollgard II® cotton was quantified using Enzyme Linked Immunosorbent Assays (ELISA) method. The ELISA technique involves binding a sample or calibrator to a solid-phase antibody, forming a "sandwich complex" with an enzyme-labeled antibody. The resulting enzyme substrate reaction produces a product proportional to the antigen concentration. The study reveals that each gram of Bt Bollgard II® seed powder contains 3.25 μg Cry1Ac and 182.32 μg Cry2Ab, with Cry2Ab expression 56 times higher. Variability in Cry protein expression is influenced by factors like temperature, genetic background, and plant maturity. The research emphasizes the importance of Bt plants, particularly Bt Bollgard II® seed powder as a valuable source for studying insect responses to combined Cry1Ac + Cry2Ab expression in bioassay studies.

CRISPR/Cas9-Mediated Knockout of the PxJHBP Gene Resulted in Increased Susceptibility to Bt Cry1Ac Protoxin and Reduced Lifespan and Spawning Rates in Plutella xylostella.

Juvenile hormone binding protein (JHBP) is a key regulator of JH signaling, and crosstalk between JH and 20-hydroxyecdysone (20E) can activate and fine-tune the mitogen-activated protein kinase cascade, leading to resistance to insecticidal proteins from Bacillis thuringiensis (Bt). However, the involvement of JHBP in the Bt Cry1Ac resistance of Plutella xylostella remains unclear. Here, we cloned a full-length cDNA encoding JHBP, and quantitative real-time PCR (qPCR) analysis showed that the expression of the PxJHBP gene in the midgut of the Cry1Ac-susceptible strain was significantly higher than that of the Cry1Ac-resistant strain. Furthermore, CRISPR/Cas9-mediated knockout of the PxJHBP gene significantly increased Cry1Ac susceptibility, resulting in a significantly shorter lifespan and reduced fertility. These results demonstrate that PxJHBP plays a critical role in the resistance to Cry1Ac protoxin and in the regulation of physiological metabolic processes associated with reproduction in adult females, providing valuable insights to improve management strategies of P. xylostella.

Development of a Safe and Effective Bacillus thuringiensis-Based Nanobiopesticide for Controlling Tea Pests.

Mg(OH)2 was used as the nanocarrier of the Bacillus thuringiensis (Bt) Cry1Ac protein, and the synthesized Cry1Ac-Mg(OH)2 composites were regular and uniform nanosheets. Nano-Mg(OH)2 could effectively improve the insecticidal effect of the Cry1Ac protein toward Ectropis obliqua. It could enhance the damage degree of the Cry1Ac protein to intestinal epithelial cells and microvilli, induce and enrich the production of reactive oxygen species (ROS) in the midgut, and enhance the degradation of the Cry1Ac protein into active fragments. Furthermore, an anti-rinsing assay showed that the Cry1Ac-Mg(OH)2 composites were bound to the notch structure of the tea leaf surface. The retention of the Cry1Ac protein increased by 11.45%, and sprayed nano-Mg(OH)2 was rapidly absorbed by different tissues of tea plants. Moreover, nano-Mg(OH)2 and composites did not significantly affect non-target organisms. These results show that nano-Mg(OH)2 can serve as a safe and effective biopesticide carrier, which provides a new approach for stable and efficient Bt preparation.

Incidence pattern of pink bollworm, Pectinophora gossypiella (Saund.)on different event Bt and non-Bt cottons

A field experiment was conducted at the Agricultural Research Station, Dharwad Farm, Dharwad, Karnatakaduring 2018-19 to evaluate the performance of cultivated cotton genotypes including Bt and non-Bt against pink bollworm,Pectinophora gossypiella (Saund.) under rainfed conditions. Based on seasonal mean green boll damage, Everest (13.56%)performed better against pink bollworm over single gene BG-I Bt variety PAU Bt-1 (16.55%), BG-I Bt hybrid MRC 6918(25.88%) (Both expressing Cry1Ac) and Arjun-21 Cry1A) and BG-II hybrid MRC 7918 (15.52%).DCH-32 (Non Btinterspecific hybrid) had maximum infestation of 37.59 per cent followed by H×H hybrid DHH-263 (36.34%), Suvin(21.38%), DDhc-11 (21.59%), Sahana (20.21%) and DLSa-17 (18.65%). The maximum larval recovery was 12.66 per 20green bolls in DCH-32 followed by DHH-263 (12.58) and Suvin (11.12). In general, Non-Bt genotypes had higher incidencethan Bt genotypes. Similarly, among Bt toxin, Cry1Ac and Cry2Ab expressing genotype had lower incidence.

Proteomic Analysis of Bt cry1Ac Transgenic Oilseed Rape (Brassica napus L.).

Oilseed rape (Brassica napus L.) is an important cash crop, but transgenic oilseed rape has not been grown on a commercial scale in China. It is necessary to analyze the characteristics of transgenic oilseed rape before commercial cultivation. In our study, differential expression of total protein from the leaves in two transgenic lines of oilseed rape expressing foreign Bt Cry1Ac insecticidal toxin and their non-transgenic parent plant was analyzed using a proteomic approach. Only shared changes in both of the two transgenic lines were calculated. Fourteen differential protein spots were analyzed and identified, namely, eleven upregulated expressed protein spots and three downregulated protein spots. These proteins are involved in photosynthesis, transporter function, metabolism, protein synthesis, and cell growth and differentiation. The changes of these protein spots in transgenic oilseed rape may be attributable to the insertion of the foreign transgenes. However, the transgenic manipulation might not necessarily cause significant change in proteomes of the oilseed rape.

CRISPR/Cas9-based functional characterization of PxABCB1 reveals its roles in the resistance of Plutella xylostella (L.) to Cry1Ac, abamectin and emamectin benzoate

The identification of functional midgut receptors for pesticidal proteins produced by Bacillus thuringiensis (Bt) is critical for deciphering the molecular mechanism of Bt resistance in insects. Reduced expression of the PxABCB1 gene was previously found to be associated with Cry1Ac resistance in the diamondback moth, Plutella xylostella (L.). To directly validate the potential receptor role of PxABCB1 and its contribution to Bt Cry1Ac toxicity in P. xylostella, we used CRISPR/Cas9 to generate a homozygous knockout ABCB1KO strain with a 5-bp deletion in exon 3 of its gene. The ABCB1KO strain exhibited a 63-fold resistance to Cry1Ac toxin compared to the parental DBM1Ac-S strain. Intriguingly, the ABCB1KO strain also exhibited significant increases in susceptibility to abamectin and emamectin benzoate. No changes in susceptibility to various other Bt Cry proteins or synthetic insecticides were observed. The knockout strain exhibited no significant fitness costs. Overall, our study indicates that PxABCB1 can protect the insect against avermectin insecticides on one hand, while on the other hand it facilitates the toxic effect of the Bt Cry1Ac toxin. The results of this study will help to inform integrated pest management approaches against this destructive pest.

Ten years of Cry1Ac Bt soybean use in Argentina: Historical shifts in the community of target and non-target pest insects

Long-term changes in the insect communities in genetically modified (GM) crops expressing target-specific pesticidal proteins can occur and matter for optimized integrated pest management. Using monitoring data of commercial soybean fields from 2012 to 2022, we documented shifts in the abundance of target and non-target insects of the GM Cry1Ac Bacillus thuringiensis (Bt) soybean in two provinces of northwestern Argentina. Before adoption of Bt soybean, lepidopterans prevailed in the crop-associated insect-pest community. They were 65% more abundant than stink bugs and weevils, and the highest population levels (a mean of 169 individuals/plot) were recorded during the vegetative and early reproductive stages. After introducing Bt soybean, the abundance of target lepidopterans (i.e., erebids, heliothines, and plusiines) was the lowest in the 2017–2018 crop season. In the 2020–2021 and 2021–2022 seasons, Rachiplusia nu larvae (Lepidoptera: Noctuidae: Plusiinae) were recorded in Bt soybean fields. The numbers of non-target lepidopterans (Spodoptera spp.) increased year by year, and they were the prevailing lepidopteran species on Bt soybean in 2020–2021 and the R1-R5 (reproductive) soybean growth stages. Weevil abundance was higher on Bt soybean than non-Bt soybean. Stink bugs were more frequent in Tucumán than Catamarca, and their abundances were higher during R1-R5 than during vegetative and late-reproductive stages. The temperature, precipitation, and solar radiation conditioned the abundance of some of the pest complexes. Efforts to monitor and manage secondary or Bt-resistant populations of insect pests are necessary and should be continued and complemented with studies of pest-susceptibility shifts to inform sound locally adapted integrated pest management programs.

PH-Dependent Changes in Structural Stabilities of Bt Cry1Ac Toxin and Contrasting Model Proteins following Adsorption on Montmorillonite.

The environmental fate of insecticidal Cry proteins, including time-dependent conservation of biological properties, results from their structural stability in soils. The complex cascade of reactions involved in biological action requires Cry proteins to be in solution. However, the pH-dependent changes in conformational stability and the adsorption-desorption mechanisms of Cry protein on soil minerals remain unclear. We used Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation and differential scanning calorimetry to interpret the driving forces and structural stabilities of Cry1Ac and two contrasting model proteins adsorbed by montmorillonite. The structural stability of Cry1Ac is closer to that of the "hard" protein, α-chymotrypsin, than that of the "soft" bovine serum albumin (BSA). The pH-dependent adsorption of Cry1Ac and α-chymotrypsin could be explained by DLVO theory, whereas the BSA adsorption deviated from it. Patch-controlled electrostatic attraction, hydrophobic effects, and entropy changes following protein unfolding on a mineral surface could contribute to Cry1Ac adsorption. Cry1Ac, like chymotrypsin, was partly denatured on montmorillonite, and its structural stability decreased with an increase in pH. Moreover, small changes in the conformational heterogeneity of both Cry1Ac and chymotrypsin were observed following adsorption. Conversely, adsorbed BSA was completely denatured regardless of the solution pH. The moderate conformational rearrangement of adsorbed Cry1Ac may partially explain why the insecticidal activity of Bt toxin appears to be conserved in soils, albeit for a relatively short time period.

Novel miR-108 and miR-234 target juvenile hormone esterase to regulate the response of Plutella xylostella to Cry1Ac protoxin

Insect hormones, such as juvenile hormone (JH), precisely regulate insect life-history traits. The regulation of JH is tightly associated with the tolerance or resistance to Bacillus thuringiensis (Bt). JH esterase (JHE) is a primary JH-specific metabolic enzyme which plays a key role in regulating JH titer. Here, we characterized a JHE gene from Plutella xylostella (PxJHE), and found it was differentially expressed in the Bt Cry1Ac resistant and susceptible strains. Suppression of PxJHE expression with RNAi increased the tolerance of P. xylostella to Cry1Ac protoxin. To investigate the regulatory mechanism of PxJHE, two target site prediction algorithms were applied to predict the putative miRNAs targeting PxJHE, and the resulting putative miRNAs were subsequently verified for their function targeting PxJHE using luciferase reporter assay and RNA immunoprecipitation. MiR-108 or miR-234 agomir delivery dramatically reduced PxJHE expression in vivo, whilst only miR-108 overexpression consequently increased the tolerance of P. xylostella larvae to Cry1Ac protoxin. By contrast, reduction of miR-108 or miR-234 dramatically increased PxJHE expression, accompanied by the decreased tolerance to Cry1Ac protoxin. Furthermore, injection of miR-108 or miR-234 led to developmental defects in P. xylostella, whilst injection of antagomir did not cause any obvious abnormal phenotypes. Our results indicated that miR-108 or miR-234 can be applied as potential molecular targets to combat P. xylostella and perhaps other lepidopteran pests, providing novel insights into miRNA-based integrated pest management.

Managing Practical Resistance of Lepidopteran Pests to Bt Cotton in China

China is one of the major cotton producers globally with small farmers. Lepidopteran pests have always been the main factor affecting cotton production. To reduce the occurrence of and damage caused by lepidopteran pests, China has employed a pest control method focused on planting Bt (Cry1Ac) cotton since 1997. Chinese resistance management tactics for the main target pests, the cotton bollworm and pink bollworm, were also implemented. For polyphagous (multiple hosts) and migratory pests such as the cotton bollworm (Helicoverpa armigera), the "natural refuge" strategy, consisting of non-Bt crops such as corn, soybean, vegetables, peanuts, and other host crops, was adopted in the Yellow River Region (YRR) and Northwest Region (NR). For a single host and weak migration ability pest, such as the pink bollworm (Pectinophora gossypiella), the seed mix refuge strategy yields a random mixture within fields of 25% non-Bt cotton by sowing second-generation (F2) seeds. According to field monitoring results for more than 20 years in China, practical resistance (Bt cotton failure) of target pests was avoided, and there were no cases of Bt (Cry1Ac) failure of pest control in cotton production. This indicated that this Chinese resistance management strategy was very successful. The Chinese government has decided to commercialize Bt corn, which will inevitably reduce the role of natural refuges; therefore, this paper also discusses adjustments and future directions of cotton pest resistance management strategies.

Effect of Bt (Cry1Ac and Cry2Ab) and non-Bt cotton on the temporal variation of A. grandis and representatives of the Spodoptera complex in Tolima, Colombia

Transgenic cotton plants (Bacillus thuringiensis Berliner (Bt)) has significant influenced the integrated pest management around the world. In Colombia, Anthonomus grandis Boheman and Spodoptera complex are currently considered the main pests in cotton crops. Therefore, this study evaluated the effect of Bt (Cry1Ac and Cry2Ab) and non-Bt cotton on the population fluctuation during two years in Tolima region. A Pearson correlation matrix was carried out between the pest variables and yield, while climatic variables and insect populations were correlated in four phenological stages with Spearman rank correlations. Additionally, a factor analysis for mixed data was performed in order to compare the effect of genotypes on the population fluctuation of the insects. For A. grandis, no differences in their populations were presented. However, in yield non-Bt cotton plants showed a higher inverse correlation with the perforated bolls compared to Bt cotton. In relation to the Spodoptera complex, the Bt genotype had 67.4% fewer larvae compared to non-Bt cotton. Statistically significant differences were presented. However, there was not a total absence of the pest during the entire crop cycle. These results suggest that if refuge zones and pest management practices are not determined in the study area, Spodoptera complex could generate resistance to genetically modified plants.

RAPD-markers assisted genetic diversity analysis and Bt-Cry1Ac gene identification in eggplant (Solanum melongena L.)

Generic diversity (GD) screening helps to identify candidate genes involved in diseases, pests, or other stress resistance in plants. GD is crucial for maintaining vigor and healthy plant population. The random amplified polymorphic DNA (RAPD) is a rapid polymerase chain reaction (PCR)-based molecular marker, effective for screening genetic diversity in diverse plant species. In this study, we applied the RAPD-markers-assisted PCR approach to explore genetic diversity (GD) among 7 varieties of eggplant (Solanum melongena L.) at DNA level. Further, we assessed the presence of Bt-Cry1Ac gene in those varieties using the PCR approach. The eggplants showed genetic diversity at the DNA level. The amplification with two RAPD primers (OPA-02, OPA-04) produced a total of 41 bands. The highest similarity showed 78.57% among sample 4 (Eggplant China) vs sample 7 (Purple king F1) and sample 1 (Eggplant Srilanka) vs sample 4 (Eggplant China), while the lowest was 28.57% among sample 7 (Purple king F1) vs sample 3 (Eggplant Chittagong-1). In addition, the PCR results for the Bt Cry1Ac primer did not show a considerable band in the expected amplicon size. The dendrogram showed the genetic variability and relationship among all seven eggplant varieties at the genetic level. The study formulated a simple marker-based method for an effective molecular protocol to study genetics in eggplants. It also reported the presence of the Bt gene in popular eggplant varieties.

Impact of Caterpillar Increased Feeding Rates on Reduction of Bt Susceptibility

The use of insect-resistant transgenic crops producing Bacillus thuringiensis protein Cry toxins (Bt) to control caterpillars is wide-spread. Development of a mechanism to prevent Bt from reaching its target site in the digestive system could result in Bt resistance and resistance to other insecticides active per os. Increased feeding rates by increasing temperature in tobacco budworms, Chloridea virescens, and bollworms, Helicoverpa zea, decreased Bt Cry1Ac susceptibility and mortality. The same was found in C. virescens for Bollgard II plant extract containing Bt Cry1Ac and Cry2Ab2 toxins. Furthermore, H. zea from the same inbred laboratory colony that fed faster independent of temperature manipulation were less susceptible to Bt intoxication. A laboratory derived C. virescens Bt resistant strain demonstrated a higher feeding rate on non-Bt artificial diet than the parental, Bt susceptible strain. A laboratory-reared Bt resistant fall armyworm, Spodoptera frugiperda, strain also fed faster on non-Bt diet compared to Bt susceptible caterpillars of the same species, both originally collected from corn. The studies in toto and the literature reviewed support the hypothesis that increased feeding rate is a behavioral mechanism for reducing caterpillar susceptibility to Bt. Its possible role in resistance needs further study.

Development and evaluation of triple gene transgenic cotton lines expressing three genes (Cry1Ac-Cry2Ab-EPSPS) for lepidopteran insect pests and herbicide tolerance

Cotton is an international agricultural commodity and the main cash crop of Pakistan of which quality and quantity are subject to various whims of nature. Climate change, insect pest complex, and weeds are reducing its productivity. Here, we have developed triple gene cotton containing EPSPS gene along with two Bt toxin genes Cry1Ac and Cry2Ab using a strategy where all three genes are cloned in the same T-DNA, followed by successful cotton transformation via Agrobacterium-mediated transformation. This strategy has been developed to help cotton breeders in developing new cultivars by incorporating these genes into the non-transgenic or single Bt (Cry1Ac) gene cotton background where all three genes will inherit together. The expression of all three proteins was confirmed through immunostrips and was quantified through enzyme-linked immunosorbent assay (ELISA). The spatio-temporal expression of Bt protein in different parts of triple gene NIBGE cotton plants was determined. Maximum expression was found in leaves followed by seeds and boll rinds. Insect bioassays with cotton bollworms (Helicoverpa armigera), armyworms (Spodoptera litura), and pink bollworms (Pectinophora gossypiella) showed more than 90% mortality. The best performing line (NIBGE-E2) on the basis of spatiotemporal expression, glyphosate assays, and insect mortality data, was used for event characterization by using the genome sequencing approach. The event was successfully characterized and named NIBGE 20-01. A diagnostics test based on event-specific PCR was developed and its ability to distinguish NIBGE 20-01 event from other commercial transgenic cotton events was confirmed. To confirm stable expression of all three proteins in the field conditions, homozygous transgenic lines were grown in the field and the expression was confirmed through immunostrip assays. It was found that all three genes are expressed under field conditions. To show that all three genes are inherited together upon crossing with local elite cotton lines, the F1 generation was grown under glasshouse and field conditions. The expression of all three genes was confirmed under field conditions. Our results showed that transgenic cotton with three genes cloned in the same T-DNA can express all genes and can be conveniently transferred into elite cotton lines through a single cross.

Introduction of Bacillus thuringiensis (Bt) gene does not reduce potassium use efficiency of Bt transgenic cotton (Gossypium hirsutum L.)

BackgroundPotassium (K) deficiency has become a common field production problem following the widespread adoption of Bacillus thuringiensis (Bt) transgenic cotton (Gossypium hirsutum L.) worldwide. The purpose of this study was to clarify whether the introduction of Bt gene directly reduces the K-use efficiency of cotton to induce K deficiency.ResultsThe cotton variety, Jihe 321 (wild type, WT) and its two Bt (Cry1Ac)-transgenic overexpression lines (OE-29317, OE-29312) were studied in field with low soil-test K+ (47.8 mg·kg−1). In the field with low soil-test K+, only OE-29317 had less biomass and K+ accumulation than the WT at some growth stages. Both Bt lines produced similar or even greater seed cotton yield than WT in the field. When the Bt gene (~ 70%) in OE-29317 and OE-29312 plants was silenced by virus-induced gene silencing (VIGS), the VIGS-Bt plants did not produce more biomass than VIGS-green fluorescent protein (control) plants.ConclusionsThe introduction of Bt gene did not necessarily hinder the K use efficiency of the cotton lines under this study.

Effect of Transgenic Cotton Expressing Bt Cry1Ac or Cry1Ab/Ac Toxins on Lacewing Larvae Mediated by Herbivorous Insect Pests.

A simple food chain (plant, insect pests, and predatory arthropods) in an agro-ecosystem was set up here as a model system to elucidate the potential effect of transgenic Bacillus thuringiensis (Bt) cotton on non-target organisms. The system included transgenic/non-transgenic cotton, neonate larvae of three herbivorous insects (Spodoptera exigua, Helicoverpa armigera, and S. litura), and predatory lacewing larvae (Chrysopa spp.), which represent the first, second, and third trophic levels, respectively. The results showed that transgenic treatments and different densities of prey had significant effects on both body-weight gain of neonate herbivorous larvae and the number of prey captured by lacewing larvae, respectively. It was found that Bt toxin could persist at the third trophic level in lacewing larvae. The diet mixture bioassay showed that body-weight gain of lacewing larvae was significantly affected by various treatments, especially at lower concentrations of plant-expressed Bt toxin in the diet mixture, which caused significant decreases in body-weight gain. In contrast, synthetic Bt toxin at higher concentrations in the diet did not show this effect. Thus, we inferred that Bt toxin indirectly affected the growth of the lacewings and the lacewings may not be susceptible to Bt toxin or are able to metabolize it.

A single transcription factor facilitates an insect host combating Bacillus thuringiensis infection while maintaining fitness

Maintaining fitness during pathogen infection is vital for host survival as an excessive response can be as detrimental as the infection itself. Fitness costs are frequently associated with insect hosts countering the toxic effect of the entomopathogenic bacterium Bacillus thuringiensis (Bt), which delay the evolution of resistance to this pathogen. The insect pest Plutella xylostella has evolved a mechanism to resist Bt toxins without incurring significant fitness costs. Here, we reveal that non-phosphorylated and phosphorylated forms of a MAPK-modulated transcription factor fushi tarazu factor 1 (FTZ-F1) can respectively orchestrate down-regulation of Bt Cry1Ac toxin receptors and up-regulation of non-receptor paralogs via two distinct binding sites, thereby presenting Bt toxin resistance without growth penalty. Our findings reveal how host organisms can co-opt a master molecular switch to overcome pathogen invasion with low cost, and contribute to understanding the underlying mechanism of growth-defense tradeoffs during host-pathogen interactions in P. xylostella.