Bombyx mori midgut membrane protein P252, which binds to Bacillus thuringiensis Cry1A, is a chlorophyllide-binding protein, and the resulting complex has antimicrobial activity

Arabidopsis Transcriptomics Reveals the Role of Lipoxygenase2 (AtLOX2) in Wound-Induced Responses

In wounded Arabidopsis thaliana leaves, four 13S-lipoxygenases (AtLOX2, AtLOX3, AtLOX4, AtLOX6) act in a hierarchical manner to contribute to the jasmonate burst. This leads to defense responses with LOX2 playing an important role in plant resistance against caterpillar herb-ivory. In this study, we sought to characterize the impact of AtLOX2 on wound-induced phytohormonal and transcriptional responses to foliar mechanical damage using wildtype (WT) and lox2 mutant plants. Compared with WT, the lox2 mutant had higher constitutive levels of the phytohormone salicylic acid (SA) and enhanced expression of SA-responsive genes. This suggests that AtLOX2 may be involved in the biosynthesis of jasmonates that are involved in the antagonism of SA biosynthesis. As expected, the jasmonate burst in response to wounding was dampened in lox2 plants. Generally, 1 h after wounding, genes linked to jasmonate biosynthesis, jasmonate signaling attenuation and abscisic acid-responsive genes, which are primarily involved in wound sealing and healing, were differentially regulated between WT and lox2 mutants. Twelve h after wounding, WT plants showed stronger expression of genes associated with plant protection against insect herbivory. This study highlights the dynamic nature of jasmonate-responsive gene expression and the contribution of AtLOX2 to this pathway and plant resistance against insects.

Crystal structure of the in-cell Cry1Aa purified from Bacillus thuringiensis

In-cell protein crystals which spontaneously crystallize in living cells, have recently been analyzed in investigations of their structures and biological functions. The crystals have been challenging to analyze structurally because of their small size. Therefore, the number of in-cell protein crystals in which the native structure has been determined is limited because most of the structures of in-cell crystals have been determined by recrystallization after dissolution. Some proteins have been reported to form intermolecular disulfide bonds in natural protein crystals that stabilize the crystals. Here, we focus on Cry1Aa, a cysteine-rich protein that crystallizes in Bacillus thuringiensis (Bt) and forms disulfide bonds. Previously, the full-length structure of 135 kDa Cry1Ac, which is the same size as Cry1Aa, was determined by recrystallization of dissolved protein from crystals purified from Bt cells. However, the formation of disulfide bonds has not been investigated because it was necessary to replace cysteine residues to prevent aggregation of the soluble protein. In this work, we succeeded in direct X-ray crystallographic analysis using crystals purified from Bt cells and characterized the cross-linked network of disulfide bonds within Cry1Aa crystals.

Multi-omics study and ncRNA regulation of anti-BmNPV in silkworms, Bombyx mori: an update

Bombyx mori silkworm is an important economic insect which has a significant contribution to the improvement of the economy. Bombyx mori nucleopolyhedrovirus (BmNPV) is a vitally significant purulent virus that impedes the sustainable and stable development of the silkworm industry, resulting in substantial economic losses. In recent years, with the development of biotechnology, transcriptomics, proteomics, metabolomics, and the related techniques have been used to select BmNPV-resistant genes, proteins, and metabolites. The regulatory networks between viruses and hosts have been gradually clarified with the discovery of ncRNAs, such as miRNA, lncRNA, and circRNA in cells. Thus, this paper aims to highlight the results of current multi-omics and ncRNA studies on BmNPV resistance in the silkworm, providing some references for resistant strategies in the silkworm to BmNPV.

Analysis of the Effect of Plutella xylostella Polycalin and ABCC2 Transporter on Cry1Ac Susceptibility by CRISPR/Cas9-Mediated Knockout

Many insects, including the Plutella xylostella (L.), have developed varying degrees of resistance to many insecticides, including Bacillus thuringiensis (Bt) toxins, the bioinsecticides derived from Bt. The polycalin protein is one of the potential receptors for Bt toxins, and previous studies have confirmed that the Cry1Ac toxin can bind to the polycalin protein of P. xylostella, but whether polycalin is associated with the resistance of Bt toxins remains controversial. In this study, we compared the midgut of larvae from Cry1Ac-susceptible and -resistant strains, and found that the expression of the Pxpolycalin gene was largely reduced in the midgut of the resistant strains. Moreover, the spatial and temporal expression patterns of Pxpolycalin showed that it was mainly expressed in the larval stage and midgut tissue. However, genetic linkage experiments showed that the Pxpolycalin gene and its transcript level were not linked to Cry1Ac resistance, whereas both the PxABCC2 gene and its transcript levels were linked to Cry1Ac resistance. The larvae fed on a diet containing the Cry1Ac toxin showed no significant change in the expression of the Pxpolycalin gene in a short term. Furthermore, the knockout of polycalin and ATP-binding cassette transporter subfamily C2 (ABCC2) genes separately by CRISPR/Cas9 technology resulted in resistance to decreased susceptibility to Cry1Ac toxin. Our results provide new insights into the potential role of polycalin and ABCC2 proteins in Cry1Ac resistance and the mechanism underlying the resistance of insects to Bt toxins.

The Mechanisms of Silkworm Resistance to the Baculovirus and Antiviral Breeding

Silkworm (Bombyx mori) is not only an economic insect but also a model organism for life science research. Bombyx mori nucleopolyhedrovirus (BmNPV) disease is a major infectious disease in the world's sericulture industry. The cocoon loss caused by this disease accounts for more than 60% of the total loss caused by all silkworm diseases. To date, there has been no effective solution for preventing and treating this disease. The most effective measure is to breed disease-resistant varieties. The quickest way to breed disease-resistant varieties is to apply genetic modification. However, this requires that we obtain disease resistance genes and know the mechanism of disease resistance. Since the discovery of disease-resistant resources in 1989, scholars in the sericulture industry around the world have been inspired to search for resistance genes. In the past two decades, with the help of multi-omics technologies, screening of resistance genes, gene localization, protein modification, virus-host interactions, etc., researchers have found some candidate genes that have been proposed to function at the cellular or individual level. Several disease-resistant varieties have been obtained and used in production through hybrid breeding, RNA interference, and genetic modification. This article summarizes and reviews the discovery of and research advances related to silkworm resistance to BmNPV. It is anticipated that the review will inspire scientific researchers to continue searching for disease resistance genes, clarify the molecular mechanism of silkworm disease resistance, and promote disease-resistant silkworm breeding.

Role of Lectin in the Response of Aedes aegypti Against Bt Toxin

Aedes aegypti is one of the world’s most dangerous mosquitoes, and a vector of diseases such as dengue fever, chikungunya virus, yellow fever, and Zika virus disease. Currently, a major global challenge is the scarcity of antiviral medicine and vaccine for arboviruses. Bacillus thuringiensis var israelensis (Bti) toxins are used as biological mosquito control agents. Endotoxins, including Cry4Aa, Cry4Ba, Cry10Aa, Cry11Aa, and Cyt1Aa, are toxic to mosquitoes. Insect eradication by Cry toxin relies primarily on the interaction of cry toxins with key toxin receptors, such as aminopeptidase (APN), alkaline phosphatase (ALP), cadherin (CAD), and ATP-binding cassette transporters. The carbohydrate recognition domains (CRDs) of lectins and domains II and III of Cry toxins share similar structural folds, suggesting that midgut proteins, such as C-type lectins (CTLs), may interfere with interactions among Cry toxins and receptors by binding to both and alter Cry toxicity. In the present review, we summarize the functional role of C-type lectins in Ae. aegypti mosquitoes and the mechanism underlying the alteration of Cry toxin activity by CTLs. Furthermore, we outline future research directions on elucidating the Bti resistance mechanism. This study provides a basis for understanding Bti resistance, which can be used to develop novel insecticides.

Genetic Modification Approaches for Parasporins Bacillus thuringiensis Proteins with Anticancer Activity

Bacillus thuringiensis (Bt) is a bacterium capable of producing Cry toxins, which are recognized for their bio-controlling actions against insects. However, a few Bt strains encode proteins lacking insecticidal activity but showing cytotoxic activity against different cancer cell lines and low or no cytotoxicity toward normal human cells. A subset of Cry anticancer proteins, termed parasporins (PSs), has recently arisen as a potential alternative for cancer treatment. However, the molecular receptors that allow the binding of PSs to cells and their cytotoxic mechanisms of action have not been well established. Nonetheless, their selective cytotoxic activity against different types of cancer cell lines places PSs as a promising alternative treatment modality. In this review, we provide an overview of the classification, structures, mechanisms of action, and insights obtained from genetic modification approaches for PS proteins.

Synergism of Bacillus thuringiensis Toxin Cry1Ac by a Fragment of Toxin-Binding Polycalin from Plutella xylostella

The continued success of pest control using insecticidal crystal (Cry) proteins from Bacillus thuringiensis (Bt) in transgenic plants was threatened by the evolution of resistance. Previous studies suggested that polycalin from Plutella xylostella could bind to Cry1Ac toxin as a potential receptor. In this study, a fragment of P. xylostella polycalin (Pxpolycalinf, G2209-A2942) containing a carboxyl-terminal GPI-anchored signal peptide was cloned and expressed. Purified Pxpolycalinf retained the binding ability to Cry1Ac and synergized Cry1Ac toxicity to the third larvae of P. xylostella in bioassays. Moreover, the polyclonal antibody of Pxpolycalinf decreased the Cry1Ac activity after being fed together with normal food. Further, the ELISA results showed the concentration-dependent binding of Pxpolycalinf to P. xylostella brush border membrane vesicles (BBMV). Spodoptera frugiperda 9 (Sf9) cells expressing Pxpolycalinf were not susceptive to Cry1Ac, whereas Pxpolycalinf increased Cry1Ac cytotoxicity to Sf9 cells expressing P. xylostella ATP-dependent binding cassette transporter C2 (PxABCC2). Immunolocalization presented the binding of Pxpolycalinf to the Sf9 cell membrane, and ELISA showed the concentration-dependent binding of Pxpolycalinf to Sf9 cell extraction. These results here provide the first evidence that a fragment of P. xylostella polycalin, a potential receptor of Cry1Ac, synergizes Cry1Ac toxicity to P. xylostella larvae and Sf9 cells expressing PxABCC2.

Chlorophyllides: Preparation, Purification, and Application

Chlorophyllides can be found in photosynthetic organisms. Generally, chlorophyllides have a-, b-, c-, d-, and f-type derivatives, and all chlorophyllides have a tetrapyrrole structure with a Mg ion at the center and a fifth isocyclic pentanone. Chlorophyllide a can be synthesized from protochlorophyllide a, divinyl chlorophyllide a, or chlorophyll. In addition, chlorophyllide a can be transformed into chlorophyllide b, chlorophyllide d, or chlorophyllide f. Chlorophyllide c can be synthesized from protochlorophyllide a or divinyl protochlorophyllide a. Chlorophyllides have been extensively used in food, medicine, and pharmaceutical applications. Furthermore, chlorophyllides exhibit many biological activities, such as anti-growth, antimicrobial, antiviral, antipathogenic, and antiproliferative activity. The photosensitivity of chlorophyllides that is applied in mercury electrodes and sensors were discussed. This article is the first detailed review dedicated specifically to chlorophyllides. Thus, this review aims to describe the definition of chlorophyllides, biosynthetic routes of chlorophyllides, purification of chlorophyllides, and applications of chlorophyllides.

Facile production of chlorophyllides using recombinant CrCLH1 and their cytotoxicity towards multidrug resistant breast cancer cell lines

The purity of chlorophylls plays one of the key role for the production of chlorophyllides. We have designed a facile method for chlorophyll purification by twice solvent extraction. Twice extraction causes the loss of chlorophylls, but the purity of total chlorophylls can be enhanced 182%. Then, the purified chlorophylls can be converted to relatively pure chlorophyllides facilely. The results show that higher purity of chlorophyllides could be obtained when purified chlorophylls (ethanol-hexane extract) was used as starting materials than that of crude chlorophylls (ethanol-only extract). In biocompatibility test, the results showed that the prepared chlorophyllides can be applied as biomaterials. When the prepared chlorophyllides were applied to anticancer tests, they were active both in MCF7 and MDA-MB-231 (multidrug resistant breast cancer cells) cell lines. In addition, the results suggested that the prepared chlorophyllides could be a potential candidate of combination therapy with doxorubicin to breast cancers.

The fate of chlorophyll in phytophagous insects goes beyond nutrition

Chlorophyll (Chl) is a natural compound that is found in all autotrophic plants. Since phytophagous insects ingest the photosynthetically active material with the plant leaves, the question arises if and how herbivores deal with Chl and its degradation products. Here we review findings on Chl degradation in phytophagous insects and highlight the role of these ubiquitous plant metabolites for plant-feeding insects. Due to the anaerobic gut of many insects, the degradation is limited to the removal of the peripheral substituents, while the tetrapyrrole core remains intact. Proteins, such as red fluorescent protein, P252 (a novel 252-kDa protein), and chlorophyllide binding protein have been reported to occur in the insect gut and might be indirectly connected to Chl degradation. Besides of an nutritional value, e.g., by taking up Mg²⁺ ions or by sequestration of carbon from the phytol side chain, the Chl degradation products may serve the insect, after binding to certain proteins, as antimicrobial, antifungal, and antiviral factors. The protein complexes may also confer protection against reactive oxygen species. The antibiotic potential of proteins and degradation products does not only benefit phytophagous insects but also human being in medical application of cancer treatment for instance. This review highlights these aspects from a molecular, biochemical, and ecological point of view.

Polycalin is involved in the toxicity and resistance to Cry1Ac toxin in Helicoverpa armigera (Hübner)

Polycalin has been confirmed as a binding protein of the Cry toxins in a few Lepidoptera insects, but its function in the action mechanism of Cry1Ac and whether it is involved in resistance evolution are still unclear. In this study, Ligand blot and enzyme-linked immunosorbent assays showed that Helicoverpa armigera polycalin could specifically interact with Cry1Ac with a high affinity (K_d  = 118.80 nM). Importantly, antisera blocking polycalin in H. armigera larvae decreased the toxicity of Cry1Ac by 31.84%. Furthermore, the relative gene and protein expressions were lower in Cry1Ac-resistant strain (LF60) than that in Cry1Ac-susceptible strain (LF). These findings indicated that H. armigera polycalin was a possible receptor of Cry1Ac and may be contributed to the resistance to Cry1Ac.

Identification of ABCC2 as a binding protein of Cry1Ac on brush border membrane vesicles from Helicoverpa armigera by an improved pull-down assay

Cry1Ac toxin‐binding proteins from Helicoverpa armigera brush border membrane vesicles were identified by an improved pull‐down method that involves coupling Cry1Ac to CNBr agarose combined with liquid chromatography–tandem mass spectrometry (LC‐MS/MS). According to the LC‐MS/MS results, Cry1Ac toxin could bind to six classes of aminopeptidase‐N, alkaline phosphatase, cadherin‐like protein, ATP‐binding cassette transporter subfamily C protein (ABCC2), actin, ATPase, polycalin, and some other proteins not previously characterized as Cry toxin‐binding molecules such as dipeptidyl peptidase or carboxyl/choline esterase and some serine proteases. This is the first report that suggests the direct binding of Cry1Ac toxin to ABCC2 in H. armigera.

The Green Gut: Chlorophyll Degradation in the Gut of Spodoptera littoralis

Chlorophylls, the most prominent natural pigments, are part of the daily diet of herbivorous insects. The spectrum of ingested and digested chlorophyll metabolites compares well to the pattern of early chlorophyll-degradation products in senescent plants. Intact chlorophyll is rapidly degraded by proteins in the front- and midgut. Unlike plants, insects convert both chlorophyll a and b into the corresponding catabolites. MALDI-TOF/MS imaging allowed monitoring the distribution of the chlorophyll catabolites along the gut of Spodoptera littoralis larvae. The chlorophyll degradation in the fore- and mid-gut is strongly pH dependent, and requires alkaline conditions. Using LC-MS/MS analysis we identified a lipocalin-type protein in the intestinal fluid of S. littoralis homolog to the chlorophyllide a binding protein from Bombyx mori. Widefield and high-resolution autofluorescence microscopy revealed that the brush border membranes are covered with the chlorophyllide binding protein tightly bound via its GPI-anchor to the gut membrane. A function in defense against gut microbes is discussed.

Reexamination of chlorophyllase function implies its involvement in defense against chewing herbivores

Chlorophyllase (CLH) is a common plant enzyme that catalyzes the hydrolysis of chlorophyll to form chlorophyllide, a more hydrophilic derivative. For more than a century, the biological role of CLH has been controversial, although this enzyme has been often considered to catalyze chlorophyll catabolism during stress-induced chlorophyll breakdown. In this study, we found that the absence of CLH does not affect chlorophyll breakdown in intact leaf tissue in the absence or the presence of methyl-jasmonate, which is known to enhance stress-induced chlorophyll breakdown. Fractionation of cellular membranes shows that Arabidopsis (Arabidopsis thaliana) CLH is located in the endoplasmic reticulum and the tonoplast of intact plant cells. These results indicate that CLH is not involved in endogenous chlorophyll catabolism. Instead, we found that CLH promotes chlorophyllide formation upon disruption of leaf cells, or when it is artificially mistargeted to the chloroplast. These results indicate that CLH is responsible for chlorophyllide formation after the collapse of cells, which led us to hypothesize that chlorophyllide formation might be a process of defense against chewing herbivores. We found that Arabidopsis leaves with genetically enhanced CLH activity exhibit toxicity when fed to Spodoptera litura larvae, an insect herbivore. In addition, purified chlorophyllide partially suppresses the growth of the larvae. Taken together, these results support the presence of a unique binary defense system against insect herbivores involving chlorophyll and CLH. Potential mechanisms of chlorophyllide action for defense are discussed.

Expression analysis of chlorophyllid α binding protein, a secretory, red fluorescence protein in the midgut of silkworm, Bombyx mori

Chlorophyllid α binding protein (chbp) was recently characterized by its ability to bind the prosthetic group of chlorophylls and little information is known regarding its expression. In the present study, we found that chpb was expressed highly and exclusively in the midgut of silkworm, Bombyx mori. The expression level of chbp was very high in the newly molted fifth instar larvae followed by gradual decline in the same instar. Our results demonstrated that CHBP was a secretory protein and located mainly in the apical of midgut epithelial cells. Real-time polymerase chain reaction analysis results showed that chpb highly expressed in the anterior midgut, threefold and sixfold higher compared with that of the middle midgut and posterior midgut, respectively, and chpb expression declined in darkness. In addition, the expression of chbp was affected by high-dose virus or bacterium infection.

Shotgun analysis on the peritrophic membrane of the silkworm Bombyx mori

The insect midgut epithelium is generally lined with a unique chitin and protein structure, the peritrophic membrane (PM), which facilitates food digestion and protects the gut epithelium. We used gel electrophoresis and mass spectrometry to identify the extracted proteins from the silkworm PM to obtain an in-depth understanding of the biological function of the silkworm PM components. A total of 305 proteins, with molecular weights ranging from 8.02 kDa to 788.52 kDa and the isoelectric points ranging from 3.39 to 12.91, were successfully identified. We also found several major classes of PM proteins, i.e. PM chitin-binding protein, invertebrate intestinal mucin, and chitin deacetylase. The protein profile provides a basis for further study of the physiological events in the PM of Bombyx mori. [BMB Reports 2012; 45(11): 665-670]

Single amino acid mutation in an ATP-binding cassette transporter gene causes resistance to Bt toxin Cry1Ab in the silkworm, Bombyx mori

Bt toxins derived from the arthropod bacterial pathogen Bacillus thuringiensis are widely used for insect control as insecticides or in transgenic crops. Bt resistance has been found in field populations of several lepidopteran pests and in laboratory strains selected with Bt toxin. Widespread planting of crops expressing Bt toxins has raised concerns about the potential increase of resistance mutations in targeted insects. By using Bombyx mori as a model, we identified a candidate gene for a recessive form of resistance to Cry1Ab toxin on chromosome 15 by positional cloning. BGIBMGA007792-93, which encodes an ATP-binding cassette transporter similar to human multidrug resistance protein 4 and orthologous to genes associated with recessive resistance to Cry1Ac in Heliothis virescens and two other lepidopteran species, was expressed in the midgut. Sequences of 10 susceptible and seven resistant silkworm strains revealed a common tyrosine insertion in an outer loop of the predicted transmembrane structure of resistant alleles. We confirmed the role of this ATP-binding cassette transporter gene in Bt resistance by converting a resistant silkworm strain into a susceptible one by using germline transformation. This study represents a direct demonstration of Bt resistance gene function in insects with the use of transgenesis.

The profiles of red fluorescent proteins with antinucleopolyhedrovirus activity in races of the silkworm Bombyx mori

Partially purified red fluorescent proteins (RFPs) secured from the gut juice of 5th-instar multivoltine and bivoltine silkworm races were observed as several bands in electrophoretograms and chromatographic eluates. Interestingly, different races of silkworms had varying numbers of fluorescent protein bands: 11 in Pure Mysore (resistant), 11 in Nistari (resistant), 4 in CSR(2) (moderately susceptible) and 1 in NB(4)D(2) (highly susceptible). Bioassay experiments indicated that the fluorescent bands had antinucleopolyhedrovirus (antiNPV) activity. The molar extinction coefficients and fluorescence quantum yields of all RFPs were estimated. The purified tetrapyrroles were characterized by UV-visible absorption and fluorescence spectral analyses. All tetrapyrrole moieties associated with RFPs were found to be different and characteristic of the fluorescent bands. The resulting qualitative and quantitative differences among the individual RFPs from various races of silkworm were related to the susceptibilities of the silkworms to the viral disease. Moreover, light was found to be essential for the synthesis of RFPs, and, therefore, the role of light in the synthesis of RFPs was evaluated. Thus, this work may elucidate the process of RFP synthesis in silkworm, which may be used as a biomarker to measure the degree of susceptibility of silkworm races to NPV. Therefore, the characteristic band pattern may be used as an indicator to define the relative resistance of a race towards the specific virus.

Proteomic analysis of peritrophic membrane (PM) from the midgut of fifth-instar larvae, Bombyx mori

The insect peritrophic membrane (PM), separating midgut epithelium and intestinal contents, is protective lining for the epithelium and plays the important role in absorption of nutrients, and also is the first barrier to the pathogens ingested through oral feeding. In order to understand the biological function of silkworm larval PM, shotgun liquid chromatography tandem mass spectrometry (LC-MS/MS) approach was applied to investigate its protein composition. Total 47 proteins were identified, of which 51.1% of the proteins had the isoelectric point (pI) within the range of 5-7, and 53.2% had molecular weights within the range 15-45 kDa. Most of them were found to be closely related to larval nutrients metabolism and innate immunity. Furthermore, these identified proteins were annotated according to Gene Ontology Annotation in terms of molecular function, biological process and cell localization. Most of the proteins had catalytic activity, binding activity and transport function. The knowledge obtained from this study will favour us to well understand the role of larval PM in larval physiological activities, and also help us to find the potential target and design better biopesticides to control pest, particularly the Lepidoptera insect.

Bacillus thuringiensis: A story of a successful bioinsecticide

Bacillus thuringiensis (Bt) bacteria are insect pathogens that rely on insecticidal pore forming proteins known as Cry and Cyt toxins to kill their insect larval hosts. At least four different non-structurally related families of proteins form the Cry toxin group of toxins. The expression of certain Cry toxins in transgenic crops has contributed to an efficient control of insect pests resulting in a significant reduction in chemical insecticide use. The mode of action of the three domain Cry toxin family involves sequential interaction of these toxins with several insect midgut proteins facilitating the formation of a pre-pore oligomer structure and subsequent membrane insertion that leads to the killing of midgut insect cells by osmotic shock. In this manuscript we review recent progress in understanding the mode of action of this family of proteins in lepidopteran, dipteran and coleopteran insects. Interestingly, similar Cry-binding proteins have been identified in the three insect orders, as cadherin, aminopeptidase-N and alkaline phosphatase suggesting a conserved mode of action. Also, recent data on insect responses to Cry toxin attack is discussed. Finally, we review the different Bt based products, including transgenic crops, that are currently used in agriculture.

An ABC transporter mutation is correlated with insect resistance to Bacillus thuringiensis Cry1Ac toxin

Transgenic crops producing insecticidal toxins from Bacillus thuringiensis (Bt) are commercially successful in reducing pest damage, yet knowledge of resistance mechanisms that threaten their sustainability is incomplete. Insect resistance to the pore-forming Cry1Ac toxin is correlated with the loss of high-affinity, irreversible binding to the mid-gut membrane, but the genetic factors responsible for this change have been elusive. Mutations in a 12-cadherin-domain protein confer some Cry1Ac resistance but do not block this toxin binding in in vitro assays. We sought to identify mutations in other genes that might be responsible for the loss of binding. We employed a map-based cloning approach using a series of backcrosses with 1,060 progeny to identify a resistance gene in the cotton pest Heliothis virescens that segregated independently from the cadherin mutation. We found an inactivating mutation of the ABC transporter ABCC2 that is genetically linked to Cry1Ac resistance and is correlated with loss of Cry1Ac binding to membrane vesicles. ABC proteins are integral membrane proteins with many functions, including export of toxic molecules from the cell, but have not been implicated in the mode of action of Bt toxins before. The reduction in toxin binding due to the inactivating mutation suggests that ABCC2 is involved in membrane integration of the toxin pore. Our findings suggest that ABC proteins may play a key role in the mode of action of Bt toxins and that ABC protein mutations can confer high levels of resistance that could threaten the continued utilization of Bt-expressing crops. However, such mutations may impose a physiological cost on resistant insects, by reducing export of other toxins such as plant secondary compounds from the cell. This weakness could be exploited to manage this mechanism of Bt resistance in the field.

A promising broad spectrum antimicrobial red fluorescent protein present in silkworm excreta

The purified silkworm excretory red fluorescent protein (SE-RFP) has exhibited a potent broad spectrum antimicrobial activity. The anti-microbial assays of purified SE-RFP against several pathogenic bacterial (both Gram positive and Gram negative) and fungal strains were performed by agar cup plate method. The minimum inhibitory concentration (MIC) of SE-RFP against pathogenic bacteria and fungi was evaluated by agar dilution technique. The SE-RFP has exhibited highest activity (lowest minimum inhibitory concentration and largest zone of inhibition) against Staphylococcus aureus and Candida albicans among the tested bacteria and fungi, respectively. For the first time, we are reporting here the bioactivity of a red fluorescent protein purified from the silkworm excreta against clinically important bacteria and fungi. The bioactive SE-RFP has two absorption peaks at 280 and 603 nm and, it has exhibited fluorescence emission peaks at 334 and 619 nm upon exciting at 280 and 603 nm, respectively. The SE-RFP being an aqua-soluble, economically feasible and eco-friendly protein, it can therefore be used for the practical applications as an effective antimicrobial agent.

A genome-wide survey for host response of silkworm, Bombyx mori during pathogen Bacillus bombyseptieus infection

Host-pathogen interactions are complex relationships, and a central challenge is to reveal the interactions between pathogens and their hosts. Bacillus bombysepticus (Bb) which can produces spores and parasporal crystals was firstly separated from the corpses of the infected silkworms (Bombyx mori). Bb naturally infects the silkworm can cause an acute fuliginosa septicaemia and kill the silkworm larvae generally within one day in the hot and humid season. Bb pathogen of the silkworm can be used for investigating the host responses after the infection. Gene expression profiling during four time-points of silkworm whole larvae after Bb infection was performed to gain insight into the mechanism of Bb-associated host whole body effect. Genome-wide survey of the host genes demonstrated many genes and pathways modulated after the infection. GO analysis of the induced genes indicated that their functions could be divided into 14 categories. KEGG pathway analysis identified that six types of basal metabolic pathway were regulated, including genetic information processing and transcription, carbohydrate metabolism, amino acid and nitrogen metabolism, nucleotide metabolism, metabolism of cofactors and vitamins, and xenobiotic biodegradation and metabolism. Similar to Bacillus thuringiensis (Bt), Bb can also induce a silkworm poisoning-related response. In this process, genes encoding midgut peritrophic membrane proteins, aminopeptidase N receptors and sodium/calcium exchange protein showed modulation. For the first time, we found that Bb induced a lot of genes involved in juvenile hormone synthesis and metabolism pathway upregulated. Bb also triggered the host immune responses, including cellular immune response and serine protease cascade melanization response. Real time PCR analysis showed that Bb can induce the silkworm systemic immune response, mainly by the Toll pathway. Anti-microorganism peptides (AMPs), including of Attacin, Lebocin, Enbocin, Gloverin and Moricin families, were upregulated at 24 hours post the infection.

A unique red fluorescent protein of silkworm bearing two photochromic moieties

A silkworm excretory red fluorescent protein (SE-RFP) having light-dependent activity against Bombyx mori nucleopolyhedrovirus (BmNPV) was purified. Light was observed to be essential also for the SE-RFP synthesis as it was produced only when silkworms were reared in light. SE-RFP has exhibited a high fluorescence quantum yield of 0.86. The apparent mass of native SE-RFP was about 1100 kDa as analysed by gel filtration chromatography. Two photochromic moieties associated with the SE-RFP, namely tetrapyrrole-I (TP-I) and tetrapyrrole-II (TP-II), were isolated by employing TLC and HPTLC techniques. The purified tetrapyrroles were characterized by UV-absorption, fluorescence, atomic absorption and FT-IR spectral analyses. The molecular masses of TP-I and TP-II were 535 and 870 Da, respectively, as determined by ESI-MS and MALDI-TOF-MS. The molar ratio of TP-I to TP-II was 1.14 : 1.00, and a total of 7.251 micromol tetrapyrroles (TP-I + TP-II) were found to be present per mg of SE-RFP. TP-I and TP-II were identified as chlorophyll derivatives, namely, pyropheophorbide a and pheophytin a, respectively. Hence, the SE-RFP was concluded to be a unique insect red fluorescent protein having two photochromic moieties and potent photobiological activity.

Proteomic analysis of the peritrophic matrix from the gut of the caterpillar, Helicoverpa armigera

The peritrophic matrix from the midgut of the caterpillar, Helicovera armigera, was solubilized by treatment with anhydrous trifluoromethanesulfonic acid, apparently by depolymerisation of its chitin component. This allowed the efficient extraction of proteins in a technique that may be broadly applicable to the analysis of other structures containing chitin. Gel electrophoresis and mass spectrometry of tryptic peptides were used to identify the extracted proteins with gut-expressed cDNA sequences. The major proteins of this cohesive, digestion-resistant structure are chitin deacetylase-like and mucin-like proteins, the latter with multiple chitin-binding domains that may cross-link chitin fibrils to provide a barrier against abrasive food particles and parasites, one of the major functions of the matrix. Other proteins found in the H. armigera gut peritrophic matrix suggest that the matrix is a dynamic, complex structure that may participate in the immobilization of digestive enzymes, actively protect the gut from parasite invasion and intercept toxins such as lectins and Bacillus thuringiensis crystal proteins.