Decrease in the expression level of the gene encoding the putative Bombyx mori bidensovirus receptor during virus infection.

Bombyx mori bidensovirus (BmBDV) is a pathogen that replicates only in the midgut columnar cells of silkworms, causing fatal disease. Resistance to BmBDV, which does not depend on the viral dose, is determined by a single gene, nsd-2 (resistance gene). Previously, we identified nsd-2 by positional cloning using B. mori genome information and found that this gene encodes a putative amino acid transporter that may function as a receptor for BmBDV. In this study, to understand the relationship between BmBDV and the putative virus receptor, we performed expression analysis of +nsd-2 (allele of nsd-2; susceptibility gene) after virus infection. Quantitative RT-PCR analysis using total RNA isolated from the midgut of an uninfected and a virus-infected silkworm revealed no change in the expression levels of +nsd-2 in the uninfected silkworm, whereas the expression levels of +nsd-2 drastically decreased in the virus-infected silkworm. Moreover, comparison of the expression pattern between the BmBDV-derived transcript and +nsd-2 revealed that the expression level of +nsd-2 decreased with an increase in the virus-derived transcript. In addition, expression analysis of 26 genes encoding other transporters in the midgut demonstrated that the expression levels of three other genes also decreased similarly to the decrease of the expression levels of +nsd-2 after virus infection. Thus, our results suggest that some transporters, including +nsd-2, are affected by BmBDV infection.

Characterization and genome comparison of an Indian isolate of bidensovirus infecting the silkworm Bombyx mori.

The bipartite genome of an Indian isolate of Bombyx mori bidensovirus (BmBDV), one of the causative agents of the fatal silkworm disease 'Flacherie', was cloned and completely sequenced. Nucleotide sequence analysis of this Indian isolate of BmBDV revealed two viral DNA segments, VD1 and VD2 as well as a DNA polymerase motif which supports its taxonomical status as the type species of a new family of Bidnaviridae. The Indian isolate of BmBDV was found to have a total of six putative ORFs four of which were located on the VD1 with the other two being on the VD2 DNA segment. The VD1 DNA segment was found to code for three non-structural proteins including a viral DNA polymerase as well as one structural protein, while the VD2 DNA segment was found to code for one structural and one non-structural protein, similar to that of the Japanese and Zhenjiang isolates of BmBDV. A BmBDV ORF expression study was done through real time qPCR wherein the VD2 ORF 1 and 2 showed the maximum transcript levels. This is the first report of the genome characterization of an Indian isolate of BmBDV, infecting silkworm B. mori.

Gene expression and localization analysis of Bombyx mori bidensovirus and its putative receptor in B. mori midgut.

Bombyx mori bidensovirus (BmBDV), which causes fatal flacherie disease in the silkworm, replicates only in midgut columnar cells. The viral resistance expressed by some silkworm strains, which is characterized as non-susceptibility irrespective of the viral dose, is determined by a single gene, nsd-2. We previously identified nsd-2 by positional cloning and found that this gene encodes a putative amino acid transporter that might function as a receptor for BmBDV. In this study, we investigated the relationship between the part of the midgut expressing nsd-2 (resistance gene), +(nsd-2) (susceptibility gene) and BmBDV propagation. Quantitative RT-PCR (qRT-PCR) analysis using total RNA isolated from the anterior, middle, and posterior parts of the midgut showed that nsd-2 and +(nsd-2) were strongly expressed in the posterior part of the midgut. The expression levels of both genes were very low in the anterior and middle parts. The qRT-PCR analysis showed that the expression levels of BmBDV-derived transcripts were correlated with the levels of +(nsd-2) expression. However, BmBDV-derived transcripts were clearly detected in all parts of the midgut. These results suggest that the infectivity of BmBDV depends mainly on the expression level of +(nsd-2) in the midgut and that viral infection is supported even by very faint expression of +(nsd-2). By contrast, the expression levels of +(nsd-2) were exceedingly low or undetectable in the middle part of the midgut, indicating that BmBDV infection might occur via another mechanism, independent of +(nsd-2), in the middle part of the midgut.

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.

Detailed investigation of the sequential pathological changes in silkworm larvae infected with Bombyx densovirus type 1.

Bombyx mori densovirus type 1 (BmDNV-1) is a pathogen causing flacherie disease in silkworms. BmDNV-1 multiplies only in the nuclei of the columnar cells of larval midgut epithelium. Although several immunohistochemical studies using anti-BmDNV-1 antibody have been reported to date, sequential pathological changes in BmDNV-1-infected larvae have not been completely elucidated. In this paper, sequential investigations were performed on the pathological features of BmDNV-1-infected larvae and BmDNV-1 propagation. Oral infection experiments using newly ecdysed 4th instar larvae revealed that the larvae began to die 9 days post infection (dpi), and the remaining died 10 dpi. Histological observations revealed phenotypic alterations in the midgut cells from 4 dpi, and complete disruption of the midgut structure at 9 dpi. Quantitative RT-PCR of two BmDNV-1 genes indicated that BmDNV-1 began to propagate from 4 dpi, and gradually increased until the larvae died. These expression patterns revealed marked correlation with the histological changes observed in the virus-infected midgut cells. Moreover, bioassays using larvae at various developmental stages clearly indicated that the pathogenicity of this virus is not dependent on the larval stage or the molting process.

Repression of tyrosine hydroxylase is responsible for the sex-linked chocolate mutation of the silkworm, Bombyx mori.

Pigmentation patterning has long interested biologists, integrating topics in ecology, development, genetics, and physiology. Wild-type neonatal larvae of the silkworm, Bombyx mori, are completely black. By contrast, the epidermis and head of larvae of the homozygous recessive sex-linked chocolate (sch) mutant are reddish brown. When incubated at 30 degrees C, mutants with the sch allele fail to hatch; moreover, homozygous mutants carrying the allele sch lethal (sch(l)) do not hatch even at room temperature (25 degrees C). By positional cloning, we narrowed a region containing sch to 239,622 bp on chromosome 1 using 4,501 backcross (BC1) individuals. Based on expression analyses, the best sch candidate gene was shown to be tyrosine hydroxylase (BmTh). BmTh coding sequences were identical among sch, sch(l), and wild-type. However, in sch the approximately 70-kb sequence was replaced with approximately 4.6 kb of a Tc1-mariner type transposon located approximately 6 kb upstream of BmTh, and in sch(l), a large fragment of an L1Bm retrotransposon was inserted just in front of the transcription start site of BmTh. In both cases, we observed a drastic reduction of BmTh expression. Use of RNAi with BmTh prevented pigmentation and hatching, and feeding of a tyrosine hydroxylase inhibitor also suppressed larval pigmentation in the wild-type strain, pnd(+) and in a pS (black-striped) heterozygote. Feeding L-dopa to sch neonate larvae rescued the mutant phenotype from chocolate to black. Our results indicate the BmTh gene is responsible for the sch mutation, which plays an important role in melanin synthesis producing neonatal larval color.

Positional cloning of a gene responsible for the cts mutation of the silkworm, Bombyx mori.

The larval head cuticle and anal plates of the silkworm mutant cheek and tail spot (cts) have chocolate-colored spots, unlike the entirely white appearance of the wild-type (WT) strain. We report the identification and characterization of the gene responsible for the cts mutation. Positional cloning revealed a cts candidate on chromosome 16, designated BmMFS, based on the high similarity of the deduced amino acid sequence between the candidate gene from the WT strain and the major facilitator superfamily (MFS) protein. BmMFS likely encodes a membrane protein with 11 putative transmembrane domains, while the putative structure deduced from the cts-type allele possesses only 10-pass transmembrane domains owing to a deletion in its coding region. Quantitative RT-PCR analysis showed that BmMFS mRNA was strongly expressed in the integument of the head and tail, where the cts phenotype is observed; expression markedly increased at the molting and newly ecdysed stages. These results indicate that the novel BmMFS gene is cts and the membrane structure of its protein accounts for the cts phenotype. These expression profiles and the cts phenotype are quite similar to those of melanin-related genes, such as Bmyellow-e and Bm-iAANAT, suggesting that BmMFS is involved in the melanin synthesis pathway.

Resistance mechanism of Nid-1, a dominant non-susceptibility gene, against Bombyx mori densovirus 1 infection.

Bombyx mori densovirus 1 (BmDV1) is a pathogen that causes flacherie disease in mulberry silkworms (B. mori). The absolute resistance (non-susceptibility) to BmDV1 of certain silkworm strains is determined independently by two genes, nsd-1 and Nid-1. Previously, we investigated the expression of viral transcript in virus-inoculated silkworms carrying different nsd-1 and Nid-1 genotypes, and observed that nsd-1 and Nid-1 expression blocked the early and late steps of BmDV1 infection, respectively. In addition, we found that nsd-1 encoded a Bombyx-specific mucin-like membrane protein only present on the surface of the midgut, where BmDV1 could infect. In this study, we dissected the resistance mechanism by Nid-1 against BmDV1 infection by investigating the sequential changes in the accumulation of viral DNA, transcripts, and proteins derived from BmDV1 in susceptible strain (pxj) and Nid-1-carrying resistant strain (No. 908) after inoculation with BmDV1. Genomic PCR results showed that the BmDV1 DNA was detected immediately after the infection in both strains but rapidly decreased in the Nid-1-carrying strain No. 908 compared with the susceptible strain pxj. RT-PCR results also showed that the BmDV1 transcripts of Nid-1-carrying strain No. 908 were rapidly decreased after the infection. Moreover, BmDV1-derived proteins were not detected in No. 908 throughout the infection. These results suggest that Nid-1 expression might inhibit the accumulation of viral DNA and transcripts. As Nid-1 has not been molecularly characterized, its identification will contribute to the elucidation of the interactions between the silkworm and BmDV1.

Yellow-e determines the color pattern of larval head and tail spots of the silkworm Bombyx mori.

Yellow proteins form a large family in insects. In Drosophila melanogaster, there are 14 yellow genes in the genome. Previous studies have shown that the yellow gene is necessary for normal pigmentation; however, the roles of other yellow genes in body coloration are not known. Here, we provide the first evidence that yellow-e is required for normal body color pattern in insect larvae. In two mutant strains, bts and its allele bts2, of the silkworm Bombyx mori, the larval head cuticle and anal plates are reddish brown instead of the white color found in the wild type. Positional cloning revealed that deletions in the Bombyx homolog of the Drosophila yellow-e gene (Bmyellow-e) were responsible for the bts/bts2 phenotype. Bmyellow-e mRNA was strongly expressed in the trachea, testis, and integument, and expression markedly increased at the molting stages. This profile is quite similar to that of Bmyellow, a regulator of neonatal body color and body markings in Bombyx. Quantitative reverse transcription-PCR analysis showed that Bmyellow-e mRNA was heavily expressed in the integument of the head and tail in which the bts phenotype is observed. The present results suggest that Yellow-e plays a crucial role in the pigmentation process of lepidopteran larvae.

Identification of anhydrobiosis-related genes from an expressed sequence tag database in the cryptobiotic midge Polypedilum vanderplanki (Diptera; Chironomidae).

Some organisms are able to survive the loss of almost all their body water content, entering a latent state known as anhydrobiosis. The sleeping chironomid (Polypedilum vanderplanki) lives in the semi-arid regions of Africa, and its larvae can survive desiccation in an anhydrobiotic form during the dry season. To unveil the molecular mechanisms of this resistance to desiccation, an anhydrobiosis-related Expressed Sequence Tag (EST) database was obtained from the sequences of three cDNA libraries constructed from P. vanderplanki larvae after 0, 12, and 36 h of desiccation. The database contained 15,056 ESTs distributed into 4,807 UniGene clusters. ESTs were classified according to gene ontology categories, and putative expression patterns were deduced for all clusters on the basis of the number of clones in each library; expression patterns were confirmed by real-time PCR for selected genes. Among up-regulated genes, antioxidants, late embryogenesis abundant (LEA) proteins, and heat shock proteins (Hsps) were identified as important groups for anhydrobiosis. Genes related to trehalose metabolism and various transporters were also strongly induced by desiccation. Those results suggest that the oxidative stress response plays a central role in successful anhydrobiosis. Similarly, protein denaturation and aggregation may be prevented by marked up-regulation of Hsps and the anhydrobiosis-specific LEA proteins. A third major feature is the predicted increase in trehalose synthesis and in the expression of various transporter proteins allowing the distribution of trehalose and other solutes to all tissues.

A CD36-related transmembrane protein is coordinated with an intracellular lipid-binding protein in selective carotenoid transport for cocoon coloration.

The transport pathway of specific dietary carotenoids from the midgut lumen to the silk gland in the silkworm, Bombyx mori, is a model system for selective carotenoid transport because several genetic mutants with defects in parts of this pathway have been identified that manifest altered cocoon pigmentation. In the wild-type silkworm, which has both genes, Yellow blood (Y) and Yellow cocoon (C), lutein is transferred selectively from the hemolymph lipoprotein to the silk gland cells where it is accumulated into the cocoon. The Y gene encodes an intracellular carotenoid-binding protein (CBP) containing a lipid-binding domain known as the steroidogenic acute regulatory protein-related lipid transfer domain. Positional cloning and transgenic rescue experiments revealed that the C gene encodes Cameo2, a transmembrane protein gene belonging to the CD36 family genes, some of which, such as the mammalian SR-BI and the fruit fly ninaD, are reported as lipoprotein receptors or implicated in carotenoid transport for visual system. In C mutant larvae, Cameo2 expression was strongly repressed in the silk gland in a specific manner, resulting in colorless silk glands and white cocoons. The developmental profile of Cameo2 expression, CBP expression, and lutein pigmentation in the silk gland of the yellow cocoon strain were correlated. We hypothesize that selective delivery of lutein to specific tissue requires the combination of two components: 1) CBP as a carotenoid transporter in cytosol and 2) Cameo2 as a transmembrane receptor on the surface of the cells.

Deletion of a gene encoding an amino acid transporter in the midgut membrane causes resistance to a Bombyx parvo-like virus.

Bombyx mori densovirus type 2 (BmDNV-2), a parvo-like virus, replicates only in midgut columnar cells and causes fatal disease. The resistance expressed in some silkworm strains against the virus is determined by a single gene, nsd-2, which is characterized as nonsusceptibility irrespective of the viral dose. However, the responsible gene has been unknown. We isolated the nsd-2 gene by positional cloning. The virus resistance is caused by a 6-kb deletion in the ORF of a gene encoding a 12-pass transmembrane protein, a member of an amino acid transporter family, and expressed only in midgut. Germ-line transformation with a wild-type transgene expressed in the midgut restores susceptibility, showing that the defective membrane protein is responsible for resistance. Cumulatively, our data show that the membrane protein is a functional receptor for BmDNV-2. This is a previously undescribed report of positional cloning of a mutant gene in Bombyx and isolation of an absolute virus resistance gene in insects.

Host Response against Virus Infection in an Insect: Bidensovirus Infection Effect on Silkworm (Bombyx mori).

Silk cocoons obtained from silkworms are the primary source of commercial silk, making the silkworm an economically important insect. However, the silk industry suffers significant losses due to various virus infections. Bombyx mori bidensovirus (BmBDV) is one of the pathogens that cause flacherie disease in silkworms. Most silkworm strains die after BmBDV infection. However, certain silkworm strains show resistance to the virus, which is determined by a single recessive gene, nsd-2. The +nsd-2 gene (allele of nsd-2; the susceptibility gene) encodes a putative amino acid transporter expressed only in the insect's midgut, where BmBDV can infect, suggesting that this membrane protein may function as a receptor for BmBDV. Interestingly, the expression analysis revealed no changes in the +nsd-2 gene expression levels in virus-uninfected silkworms, whereas the gene expression drastically decreased in the virus-infected silkworm. This condition indicates that the host factor's expression, the putative virus receptor, is affected by BmBDV infection. It has recently been reported that the expression levels of some host genes encoding cuticle, antioxidant, and immune response-related proteins were significantly regulated by BmBDV infection. In this review, we discuss the host response against virus infection based on our knowledge and long-term research experience in this field.

Lepidopteran wing scales contain abundant cross-linked film-forming histidine-rich cuticular proteins.

Scales are symbolic characteristic of Lepidoptera; however, nothing is known about the contribution of cuticular proteins (CPs) to the complex patterning of lepidopteran scales. This is because scales are resistant to solubilization, thus hindering molecular studies. Here we succeeded in dissolving developing wing scales from Bombyx mori, allowing analysis of their protein composition. We identified a distinctive class of histidine rich (His-rich) CPs (6%-45%) from developing lepidopteran scales by LC-MS/MS. Functional studies using RNAi revealed CPs with different histidine content play distinct and critical roles in constructing the microstructure of the scale surface. Moreover, we successfully synthesized films in vitro by crosslinking a 45% His-rich CP (BmorCPR152) with laccase2 using N-acetyl- dopamine or N-ß-alanyl-dopamine as the substrate. This molecular study of scales provides fundamental information about how such a fine microstructure is constructed and insights into the potential application of CPs as new biomaterials.

Non-susceptibility genes to Bombyx densovirus type 1, Nid-1 and nsd-1, affect distinct steps of the viral infection pathway.

In the silkworm Bombyx mori, densovirus type 1 (BmDNV-1) replicates only in the midgut and causes fatal disease. Resistance to BmDNV-1 is determined by two genes, nsd-1 and Nid-1, respectively. Neither of them has been identified yet. We investigated the viral transcript by RT-PCR in inoculated silkworms carrying different sets of nsd-1 and Nid-1 genotype. BmDNV-1 transcript was not detected in nsd-1-carrying strains irrespective of existence of Nid-1 but clearly detected in strains carrying Nid-1 without nsd-1. The result suggests that nsd-1 blocks early step of infection. On the other hand, Nid-1 does not block cell and nucleus entry and viral transcription in nuclei but blocks later step in the viral infection cycle.

KAIKObase: an integrated silkworm genome database and data mining tool.

BACKGROUND: The silkworm, Bombyx mori, is one of the most economically important insects in many developing countries owing to its large-scale cultivation for silk production. With the development of genomic and biotechnological tools, B. mori has also become an important bioreactor for production of various recombinant proteins of biomedical interest. In 2004, two genome sequencing projects for B. mori were reported independently by Chinese and Japanese teams; however, the datasets were insufficient for building long genomic scaffolds which are essential for unambiguous annotation of the genome. Now, both the datasets have been merged and assembled through a joint collaboration between the two groups. DESCRIPTION: Integration of the two data sets of silkworm whole-genome-shotgun sequencing by the Japanese and Chinese groups together with newly obtained fosmid- and BAC-end sequences produced the best continuity (~3.7 Mb in N50 scaffold size) among the sequenced insect genomes and provided a high degree of nucleotide coverage (88%) of all 28 chromosomes. In addition, a physical map of BAC contigs constructed by fingerprinting BAC clones and a SNP linkage map constructed using BAC-end sequences were available. In parallel, proteomic data from two-dimensional polyacrylamide gel electrophoresis in various tissues and developmental stages were compiled into a silkworm proteome database. Finally, a Bombyx trap database was constructed for documenting insertion positions and expression data of transposon insertion lines. CONCLUSION: For efficient usage of genome information for functional studies, genomic sequences, physical and genetic map information and EST data were compiled into KAIKObase, an integrated silkworm genome database which consists of 4 map viewers, a gene viewer, and sequence, keyword and position search systems to display results and data at the level of nucleotide sequence, gene, scaffold and chromosome. Integration of the silkworm proteome database and the Bombyx trap database with KAIKObase led to a high-grade, user-friendly, and comprehensive silkworm genome database which is now available from URL: http://sgp.dna.affrc.go.jp/KAIKObase/.

A single amino acid substitution in the Bombyx-specific mucin-like membrane protein causes resistance to Bombyx mori densovirus.

Bombyx mori densovirus type 1 (BmDV) is a pathogen that causes flacherie disease in the silkworm. The absolute nonsusceptibility to BmDV among certain silkworm strains is determined independently by two genes, nsd-1 and Nid-1. However, neither of these genes has been molecularly identified to date. Here, we isolated the nsd-1 gene by positional cloning and characterized the properties of its product, NSD-1. Sequence and biochemical analyses revealed that this gene encodes a Bombyx-specific mucin-like glycoprotein with a single transmembrane domain. The NSD-1 protein was specifically expressed in the larval midgut epithelium, the known infection site of BmDV. Sequence analysis of the nsd-1 gene from 13 resistant and 12 susceptible strains suggested that a specific arginine residue in the extracellular tail of the NSD-1 protein was common among susceptible strains. Germline transformation of the susceptible-type nsd-1 (with a single nucleotide substitution) conferred partial susceptibility to resistant larvae, indicating that the + nsd-1 gene is required for the susceptibility of B. mori larvae to BmDV and the susceptibility is solely a result of the substitution of a single amino acid with arginine. Taken together, our results provide striking evidence that a novel membrane-bound mucin-like protein functions as a cell-surface receptor for a densovirus.

Construction of a single nucleotide polymorphism linkage map for the silkworm, Bombyx mori, based on bacterial artificial chromosome end sequences.

We have developed a linkage map for the silkworm Bombyx mori based on single nucleotide polymorphisms (SNPs) between strains p50T and C108T initially found on regions corresponding to the end sequences of bacterial artificial chromosome (BAC) clones. Using 190 segregants from a backcross of a p50T female x an F1 (p50T x C108T) male, we analyzed segregation patterns of 534 SNPs between p50T and C108T, detected among 3840 PCR amplicons, each associated with a p50T BAC end sequence. This enabled us to construct a linkage map composed of 534 SNP markers spanning 1305 cM in total length distributed over the expected 28 linkage groups. Of the 534 BACs whose ends harbored the SNPs used to construct the linkage map, 89 were associated with 107 different ESTs. Since each of the SNP markers is directly linked to a specific genomic BAC clone and to whole-genome sequence data, and some of them are also linked to EST data, the SNP linkage map will be a powerful tool for investigating silkworm genome properties, mutation mapping, and map-based cloning of genes of industrial and agricultural interest.

Expression map of a complete set of gustatory receptor genes in chemosensory organs of Bombyx mori.

Most lepidopteran species are herbivores, and interaction with host plants affects their gene expression and behavior as well as their genome evolution. Gustatory receptors (Grs) are expected to mediate host plant selection, feeding, oviposition and courtship behavior. However, due to their high diversity, sequence divergence and extremely low level of expression it has been difficult to identify precisely a complete set of Grs in Lepidoptera. By manual annotation and BAC sequencing, we improved annotation of 43 gene sequences compared with previously reported Grs in the most studied lepidopteran model, the silkworm, Bombyx mori, and identified 7 new tandem copies of BmGr30 on chromosome 7, bringing the total number of BmGrs to 76. Among these, we mapped 68 genes to chromosomes in a newly constructed chromosome distribution map and 8 genes to scaffolds; we also found new evidence for large clusters of BmGrs, especially from the bitter receptor family. RNA-seq analysis of diverse BmGr expression patterns in chemosensory organs of larvae and adults enabled us to draw a precise organ specific map of BmGr expression. Interestingly, most of the clustered genes were expressed in the same tissues and more than half of the genes were expressed in larval maxillae, larval thoracic legs and adult legs. For example, BmGr63 showed high expression levels in all organs in both larval and adult stages. By contrast, some genes showed expression limited to specific developmental stages or organs and tissues. BmGr19 was highly expressed in larval chemosensory organs (especially antennae and thoracic legs), the single exon genes BmGr53 and BmGr67 were expressed exclusively in larval tissues, the BmGr27-BmGr31 gene cluster on chr7 displayed a high expression level limited to adult legs and the candidate CO2 receptor BmGr2 was highly expressed in adult antennae, where few other Grs were expressed. Transcriptional analysis of the Grs in B. mori provides a valuable new reference for finding genes involved in plant-insect interactions in Lepidoptera and establishing correlations between these genes and vital insect behaviors like host plant selection and courtship for mating.

Genomic adaptation to polyphagy and insecticides in a major East Asian noctuid pest.

The tobacco cutworm, Spodoptera litura, is among the most widespread and destructive agricultural pests, feeding on over 100 crops throughout tropical and subtropical Asia. By genome sequencing, physical mapping and transcriptome analysis, we found that the gene families encoding receptors for bitter or toxic substances and detoxification enzymes, such as cytochrome P450, carboxylesterase and glutathione-S-transferase, were massively expanded in this polyphagous species, enabling its extraordinary ability to detect and detoxify many plant secondary compounds. Larval exposure to insecticidal toxins induced expression of detoxification genes, and knockdown of representative genes using short interfering RNA (siRNA) reduced larval survival, consistent with their contribution to the insect's natural pesticide tolerance. A population genetics study indicated that this species expanded throughout southeast Asia by migrating along a South India-South China-Japan axis, adapting to wide-ranging ecological conditions with diverse host plants and insecticides, surviving and adapting with the aid of its expanded detoxification systems. The findings of this study will enable the development of new pest management strategies for the control of major agricultural pests such as S. litura.