Discovery and mapping of genomic regions governing economically important traits of Basmati rice.

BACKGROUND: Basmati rice, originated in the foothills of Himalayas, commands a premium price in the domestic and international markets on account of its unique quality traits. The complex genetic nature of unique traits of Basmati as well as tedious screening methodologies involved in quality testing have been serious constraints to breeding quality Basmati. In the present study, we made an attempt to identify the genomic regions governing unique traits of Basmati rice. RESULTS: A total of 34 Quantitative Trait Loci (QTLs) for 16 economically important traits of Basmati rice were identified employing F(2), F(3) and Recombinant Inbred Line (RIL) mapping populations derived from a cross between Basmati370 (traditional Basmati) and Jaya (semi-dwarf rice). Out of which, 12 QTLs contributing to more than 15 % phenotypic variance were identified and considered as major effect QTLs. Four major effect QTLs coincide with the already known genes viz., sd1, GS3, alk1 and fgr governing plant height, grain size, alkali spreading value and aroma, respectively. For the remaining major QTLs, candidate genes were predicted as auxin response factor for filled grains, soluble starch synthase 3 for chalkiness and VQ domain containing protein for grain breadth and grain weight QTLs, based on the presence of non-synonymous single nucleotide polymorphism (SNPs) that were identified by comparing Basmati genome sequence with that of Nipponbare. CONCLUSIONS: To the best of our knowledge, the current study is the first attempt ever made to carry out genome-wide mapping for the dissection of the genetic basis of economically important traits of Basmati rice. The promising QTLs controlling important traits in Basmati rice, identified in this study, can be used as candidates for future marker-assisted breeding.

Role of sequence encoded κB DNA geometry in gene regulation by Dorsal.

Many proteins of the Rel family can act as both transcriptional activators and repressors. However, mechanism that discerns the 'activator/repressor' functions of Rel-proteins such as Dorsal (Drosophila homologue of mammalian NFκB) is not understood. Using genomic, biophysical and biochemical approaches, we demonstrate that the underlying principle of this functional specificity lies in the 'sequence-encoded structure' of the κB-DNA. We show that Dorsal-binding motifs exist in distinct activator and repressor conformations. Molecular dynamics of DNA-Dorsal complexes revealed that repressor κB-motifs typically have A-tract and flexible conformation that facilitates interaction with co-repressors. Deformable structure of repressor motifs, is due to changes in the hydrogen bonding in A:T pair in the 'A-tract' core. The sixth nucleotide in the nonameric κB-motif, 'A' (A(6)) in the repressor motifs and 'T' (T(6)) in the activator motifs, is critical to confer this functional specificity as A(6) → T(6) mutation transformed flexible repressor conformation into a rigid activator conformation. These results highlight that 'sequence encoded κB DNA-geometry' regulates gene expression by exerting allosteric effect on binding of Rel proteins which in turn regulates interaction with co-regulators. Further, we identified and characterized putative repressor motifs in Dl-target genes, which can potentially aid in functional annotation of Dorsal gene regulatory network.

Pyrosequencing-based transcriptome analysis of the asian rice gall midge reveals differential response during compatible and incompatible interaction.

The Asian rice gall midge (Orseolia oryzae) is a major pest responsible for immense loss in rice productivity. Currently, very little knowledge exists with regard to this insect at the molecular level. The present study was initiated with the aim of developing molecular resources as well as identifying alterations at the transcriptome level in the gall midge maggots that are in a compatible (SH) or in an incompatible interaction (RH) with their rice host. Roche 454 pyrosequencing strategy was used to develop both transcriptomics and genomics resources that led to the identification of 79,028 and 85,395 EST sequences from gall midge biotype 4 (GMB4) maggots feeding on a susceptible and resistant rice variety, TN1 (SH) and Suraksha (RH), respectively. Comparative transcriptome analysis of the maggots in SH and RH revealed over-representation of transcripts from proteolysis and protein phosphorylation in maggots from RH. In contrast, over-representation of transcripts for translation, regulation of transcription and transcripts involved in electron transport chain were observed in maggots from SH. This investigation, besides unveiling various mechanisms underlying insect-plant interactions, will also lead to a better understanding of strategies adopted by insects in general, and the Asian rice gall midge in particular, to overcome host defense.

Dynamic repositioning of dorsal to two different kappaB motifs controls its autoregulation during immune response in Drosophila.

Autoregulation is one of the mechanisms of imparting feedback control on gene expression. Positive autoregulatory feedback results in induction of a gene, and negative feedback leads to its suppression. Here, we report an interesting mechanism of autoregulation operating on Drosophila Rel gene dorsal that can activate as well as repress its expression. Using biochemical and genetic approaches, we show that upon immune challenge Dorsal regulates its activation as well as repression by dynamically binding to two different kappaB motifs, kappaB(I) (intronic kappaB) and kappaB(P) (promoter kappaB), present in the dorsal gene. Although the kappaB(I) motif functions as an enhancer, the kappaB(P) motif acts as a transcriptional repressor. Interestingly, Dorsal binding to these two motifs is dynamic; immediately upon immune challenge, Dorsal binds to the kappaB(I) leading to auto-activation, whereas at the terminal phase of the immune response, it is removed from the kappaB(I) and repositioned at the kappaB(P), resulting in its repression. Furthermore, we show that repression of Dorsal as well as its binding to the kappaB(P) depends on the transcription factor AP1. Depletion of AP1 by RNA interference resulted in constitutive expression of Dorsal. In conclusion, this study suggests that during acute phase response dorsal is regulated by following two subcircuits: (i) Dl-kappaB(I) for activation and (ii) Dl-AP1-kappaB(P) for repression. These two subcircuits are temporally delineated and bring about overall regulation of dorsal during immune response. These results suggest the presence of a previously unknown mechanism of Dorsal autoregulation in immune-challenged Drosophila.

Novel female-specific splice form of dsx in the silkworm, Bombyx mori.

The Bombyx mori doublesex (Bmdsx), a homologue of doublesex of Drosophila, is the bottom most gene of the sex determination cascade. Bmdsx plays a very crucial role in somatic sexual development. Its pre-mRNA sex-specifically splices to generate two splice variants; one encodes female-specific and the other encodes male-specific polypeptides which differ only at their C-termini. The open reading frame of Bmdsx consists of 5 exons, of which exons 3 and 4 are female-specific and are skipped in males. In the present study, we have identified a third splice form of the Bmdsx which is specific only to females and differs from the previously reported Bmdsxf isoform by the presence of 15 bp sequence. This new female splice form is generated as a result of alternative 5' splice site selection in the third exon adding additional 15 bp sequence in exon 3 which results in alteration of the reading frame leading to incorporation of an early stop codon. Thus the protein encoded by this splice form is 20 aa shorter than the known BmDsxF. Initial results obtained from the study of dsx homologues in Saturniid silkmoths suggest that both the female-specific Dsx proteins are essential for female sexual differentiation. It remains to be seen whether female-specific multiple splice forms of dsx are characteristic feature of only silkmoths or widespread among lepidopterans. The findings that sex determination mechanism is unique in lepidopterans offer an opportunity to develop genetic sexing methods in beneficial as well as economically destructive lepidopteran pests.

Isolation and characterization of microsatellite loci in the Asian rice gall midge (Orseolia oryzae) (Diptera: Cecidomyiidae).

Microsatellite loci were isolated from the genomic DNA of the Asian rice gall midge, Orseolia oryzae (Wood-Mason) using a hybridization capture approach. A total of 90 non-redundant primer pairs, representing unique loci, were designed. These simple sequence repeat (SSR) markers represented di (72%), tri (15.3%), and complex repeats (12.7%). Three biotypes of gall midge (20 individuals for each biotype) were screened using these SSRs. The results revealed that 15 loci were hyper variable and showed polymorphism among different biotypes of this pest. The number of alleles ranged from two to 11 and expected heterozygosity was above 0.5. Inheritance studies with three markers (observed to be polymorphic between sexes) revealed sex linked inheritance of two SSRs (Oosat55 and Oosat59) and autosomal inheritance of one marker (Oosat43). These markers will prove to be a useful tool to devise strategies for integrated pest management and in the study of biotype evolution in this important rice pest.

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/.

Genetic relatedness does not predict the queen's successors in the primitively eusocial wasp, Ropalidia marginata.

Ropalidia marginata is a social wasp in which colonies consist of a single fertile queen and several sterile workers. If the queen is removed, one of the workers, potential queen (PQ), becomes hyperaggressive and becomes the next queen. The identity of the PQ cannot be predicted in the presence of the queen. The probability of a worker succeeding the queen is uncorrelated with her body size, dominance rank, ovarian or mating status, but imperfectly correlated with her age. Here, we investigate whether genetic relatedness help to predict the queen's successors. We constructed models based on successors being (i) most closely related to the queen, (ii) most closely related to the immediate predecessor queen/PQ, or (iii) having the highest relatedness to the majority of the workers; and (iv) having the highest average relatedness to all the workers. We predicted five successors from each of these models using pair-wise genetic relatedness estimated from polymorphic microsatellite loci. We independently performed serial queen/PQ removal experiments and compared the observed sequence of successors with the predictions from the models. The predictions of none of the models matched the experimental results; on an average 5-6 individuals predicted by the models were bypassed in the experiment. Thus, genetic relatedness is inadequate to predict the queen's successors in this species. We discuss why relatedness sometimes predicts the patterns of altruistic behaviour and sometimes not, and argue that the cost and benefit terms in Hamilton's rule, i.e. ecology, should be vigorously investigated when relatedness does not have adequate explanatory power.

Eicosapentapeptide repeats (EPRs): novel repeat proteins specific to flowering plants.

In this report, we describe a novel tandem peptide repeat protein, Eicosapentapeptide repeat (EPR), which occurs notably only in flowering plants. The EPRs are characterized by a 25 amino acid repeat unit, X(2)CX(4)CX(10)CX(2)HGGG, repeated 10 times tandemly. Sequence search revealed that the repeat motif is highly conserved across its occurrence. EPRs are predicted to exist as quasi-globular stable structures owing to highly conserved amino acid positions and potential disulfide bridges. Proteins containing EPRs are predicted to be located in chloroplasts; non-enzymatic and peptide or DNA-binding in molecular function; and they are possibly involved in transcription regulation.

Immune upregulation of novel antibacterial proteins from silkmoths (Lepidoptera) that resemble lysozymes but lack muramidase activity.

Study on immune proteins in domesticated and wild silkmoths Bombyx mori and Antheraea mylitta, respectively, led to identification of a new class of antimicrobial proteins. We designated them as lysozyme-like proteins (LLPs) owing to their partial similarity with lysozymes. However, lack of characteristic catalytic amino acid residues essential for muramidase activity in LLPs puts them functionally apart from classical lysozymes. Two LLPs, one from B. mori (BLLP1) and the other from A. mylitta (ALLP1) expressed in a recombinant system, exhibited a broad-spectrum antibacterial action. Further investigation of the antibacterial mechanism revealed that BLLP1 is bacteriostatic rather than bactericidal against Escherichia coli and Micrococcus luteus. Substantial increase in hemolymph bacterial load was observed in B. mori upon RNA interference mediated in vivo knockdown of BLLP1. We demonstrate that the antibacterial mechanism of this protein depends on peptidoglycan binding unlike peptidoglycan hydrolysis or membrane permeabilization as observed with lysozymes and most other antimicrobial peptides. To our knowledge, this is the first report on functional analysis of novel, non-catalytic lysozyme-like family of antibacterial proteins that are quite apart functionally from classical lysozymes. The present analysis holds promise for functional annotation of similar proteins from other organisms.

Simple sequence repeats in mycobacterial genomes.

Simple sequence repeats (SSRs) or microsatellites are the repetitive nucleotide sequences of motifs of length 1-6 bp. They are scattered throughout the genomes of all the known organisms ranging from viruses to eukaryotes. Microsatellites undergo mutations in the form of insertions and deletions (INDELS) of their repeat units with some bias towards insertions that lead to microsatellite tract expansion. Although prokaryotic genomes derive some plasticity due to microsatellite mutations they have in-built mechanisms to arrest undue expansions of microsatellites and one such mechanism is constituted by post-replicative DNA repair enzymes MutL, MutH and MutS. The mycobacterial genomes lack these enzymes and as a null hypothesis one could expect these genomes to harbour many long tracts. It is therefore interesting to analyse the mycobacterial genomes for distribution and abundance of microsatellites tracts and to look for potentially polymorphic microsatellites. Available mycobacterial genomes, Mycobacterium avium, M. leprae, M. bovis and the two strains of M. tuberculosis (CDC1551 and H37Rv) were analysed for frequencies and abundance of SSRs. Our analysis revealed that the SSRs are distributed throughout the mycobacterial genomes at an average of 220-230 SSR tracts per kb. All the mycobacterial genomes contain few regions that are conspicuously denser or poorer in microsatellites compared to their expected genome averages. The genomes distinctly show scarcity of long microsatellites despite the absence of a post-replicative DNA repair system. Such severe scarcity of long microsatellites could arise as a result of strong selection pressures operating against long and unstable sequences although influence of GC-content and role of point mutations in arresting microsatellite expansions can not be ruled out. Nonetheless, the long tracts occasionally found in coding as well as non-coding regions may account for limited genome plasticity in these genomes.

Capillary electrophoresis is essential for microsatellite marker based detection and quantification of adulteration of Basmati rice (Oryza sativa).

Microsatellite markers are employed for genotyping of Basmati varieties and assaying purity of market samples. However, employment of diverse electrophoresis techniques across laboratories has resulted in inconsistent allele sizes, creating doubts about the suitability of the assay. This study evaluated agarose gel electrophoresis, slab gel electrophoresis, and capillary electrophoresis techniques for their efficiency in the detection and quantification of adulteration in Basmati samples. Comparative analysis across 8 microsatellite loci in 12 rice varieties demonstrated that the capillary electrophoresis method showed less error (+/-0.73 bp) in the estimation of allele sizes compared to slab gel (+/-1.59 bp) and agarose gel (+/-8.03 bp) electrophoretic methods. Capillary electrophoresis showed greater reproducibility (<0.5 bp deviation) compared to slab gel (1 bp) and agarose (>3 bp) based methods. Capillary electrophoresis was significantly superior in quantification of the adulterant, with a mean error of +/-3.91% in comparison to slab gel (+/-6.09%). Lack of accuracy and consistency of the slab gel and agarose electrophoretic methods warrants the employment of capillary electrophoresis for Basmati rice purity assays.

Microsatellite polymorphism across the M. tuberculosis and M. bovis genomes: implications on genome evolution and plasticity.

BACKGROUND: Microsatellites are the tandem repeats of nucleotide motifs of size 1-6 bp observed in all known genomes. These repeats show length polymorphism characterized by either insertion or deletion (indels) of the repeat units, which in and around the coding regions affect transcription and translation of genes. RESULTS: Systematic comparison of all the equivalent microsatellites in the coding regions of the three mycobacterial genomes, viz. Mycobacterium tuberculosis H37Rv, Mycobacterium tuberculosis CDC1551 and Mycobacterium bovis, revealed for the first time the presence of several polymorphic microsatellites. The coding regions affected by frame-shifts owing to microsatellite indels have undergone changes indicative of gene fission/fusion, premature termination and length variation. Interestingly, the genes affected by frame-shift mutations code for membrane proteins, transporters, PPE, PE_PGRS, cell-wall synthesis proteins and hypothetical proteins. CONCLUSION: This study has revealed the role of microsatellite indel mutations in imparting novel functions and a certain degree of plasticity to the mycobacterial genomes. There seems to be some correlation between microsatellite polymorphism and the variations in virulence, host-pathogen interactions mediated by surface antigen variations, and adaptation of the pathogens. Several of the polymorphic microsatellites reported in this study can be tested for their polymorphic nature by screening clinical isolates and various mycobacterial strains, for establishing correlations between microsatellite polymorphism and the phenotypic variations among these pathogens.

MICdb: database of prokaryotic microsatellites.

The MICdb (Microsatellites Database) (http://www.cdfd.org.in/micas) is a comprehensive relational database of non-redundant microsatellites extracted from fully sequenced prokaryotic genomes. The current version (1.0) of the database has been compiled from 83 genomes belonging to different phylogenetic groups. This database has been linked to MICAS, the web-based Microstatellite Analysis Server. MICAS provides a user-friendly front-end to systematically extract data on microsatellite tracts from genomes. The database contains the following information pertaining to the microsatellites: the regions (coding/non-coding, if coding, their GenBank annotations) containing microsatellite tracts; the frequencies of their occurrences, the size and the number of repeating motifs; and the sequences of the tracts. MICAS also provides an interface to Autoprimer, a primer design program to automatically design primers for selected microsatellite loci.

Role of Bmznf-2, a Bombyx mori CCCH zinc finger gene, in masculinisation and differential splicing of Bmtra-2.

Deciphering the regulatory factors involved in Bombyx mori sex determination has been a puzzle, challenging researchers for nearly a century now. The pre-mRNA of B. mori doublesex (Bmdsx), a master regulator gene of sexual differentiation, is differentially spliced, producing Bmdsxm and Bmdsxf transcripts in males and females respectively. The putative proteins encoded by these differential transcripts orchestrate antagonistic functions, which lead to sexual differentiation. A recent study in B. mori illustrated the role of a W-derived fem piRNA in conferring femaleness. In females, the fem piRNA was shown to suppress the activity of a Z-linked CCCH type zinc finger (znf) gene, Masculiniser (masc), which indirectly promotes the Bmdsxm type of splicing. In this study, we report a novel autosomal (Chr 25) CCCH type znf motif encoding gene Bmznf-2 as one of the potential factors in the Bmdsx sex specific differential splicing, and we also provide insights into its role in the alternative splicing of Bmtra2 by using ovary derived BmN cells. Over-expression of Bmznf-2 induced Bmdsxm type of splicing (masculinisation) with a correspondingly reduced expression of Bmdsxf type isoform in BmN cells. Further, the site-directed mutational studies targeting the tandem CCCH znf motifs revealed their indispensability in the observed phenotype of masculinisation. Additionally, the dual luciferase assays in BmN cells using 5' UTR region of the Bmznf-2 strongly implied the existence of a translational repression over this gene. From these findings, we propose Bmznf-2 to be one of the potential factors of masculinisation similar to Masc. From the growing number of Bmdsx splicing regulators, we assume that the sex determination cascade of B. mori is quite intricate in nature; hence, it has to be further investigated for its comprehensive understanding.

Noduler an immune protein augments infection-induced cell proliferation through cross-talking with p38 MAPK.

Noduler, an immune protein that mediates nodule formation by binding to specific bacteria and hemocytes was previously reported in the wild tasar silkworm, Antheraea mylitta. However, the molecular mechanism underlying nodulation in lepidopterans remains unclear. The present study is performed to investigate the functional connection between Noduler with various signalling pathways. It was observed that Noduler is an upstream factor in the phenoloxidase cascade and its knockdown has no direct effect on Toll/Imd pathway inducible genes. Additionally, Noduler was shown to stimulate cell proliferation via activation of p38 mitogen-activated protein kinase (MAPK). Inhibition of p38 in the infected hemocytes cultured in vitro resulted in reduced cell proliferation and melanization. These results suggest that Noduler mediates nodulation via p38/MAPK signalling. This is the first report implicating the p38 MAPK signalling pathway in the nodulation response of insects.

Cloning and characterization of an eukaryotic initiation factor-2alpha kinase from the silkworm, Bombyx mori.

Eukaryotic initiation factor 2alpha (eIF-2alpha) kinases are involved in the translational regulations that occur in response to various types of environmental stress, and play an important role in the cellular defense system operating under unfavorable conditions. The identification of additional eIF-2alpha kinases and the elucidation of their functions are necessary to understand how different eIF-2alpha kinases can specifically respond to distinct stimuli. Here, we report a novel eIF-2alpha kinase, termed BeK, from the silkworm, Bombyx mori. This gene encodes 579 amino acids and contains all 11 catalytic domains of protein-serine/threonine kinases. Most notably, it contains an "Ile-Gln-Met-Xaa-Xaa-Cys" motif, which is highly conserved from yeast to mammalian eIF-2alpha kinases. BeK does not show any significant homology in the NH(2) terminal regulatory domain, suggesting a distinct regulatory mechanism of this novel eIF-2alpha kinase. BeK is ubiquitously expressed in the various tissues throughout the final larval stage. Importantly, BeK is activated in Drosophila Schneider cells following heat shock and osmotic stress, and activated-BeK has been shown to phosphorylate an eIF-2alpha subunit at the Ser(50) site. However, other forms of stress, such as immune stress, endoplasmic reticulum stress and oxidative stress, cannot significantly elicit BeK activity. Interestingly, the baculovirus gene product, PK2, can inhibit BeK enzymatic activity, suggesting that BeK may be an endogenous target for a viral gene product. Taken together, these data indicate that BeK is a novel eIF-2alpha kinase involved in the stress response in B. mori.

Molecular architecture of silk fibroin of Indian golden silkmoth, Antheraea assama.

The golden silk spun by Indian golden silkmoth Antheraea assama, is regarded for its shimmering golden luster, tenacity and value as biomaterial. This report describes the gene coding for golden silk H-fibroin (AaFhc), its expression, full-length sequence and structurally important motifs discerning the underlying genetic and biochemical factors responsible for its much sought-after properties. The coding region, with biased isocodons, encodes highly repetitious crystalline core, flanked by a pair of 5' and 3' non-repetitious ends. AaFhc mRNA expression is strictly territorial, confined to the posterior silk gland, encoding a protein of size 230 kDa, which makes homodimers making the elementary structural units of the fibrous core of the golden silk. Characteristic polyalanine repeats that make tight ß-sheet crystals alternate with non-polyalanine repeats that make less orderly antiparallel ß-sheets, ß-turns and partial α-helices. Phylogenetic analysis of the conserved N-terminal amorphous motif and the comparative analysis of the crystalline region with other saturniid H-fibroins reveal that AaFhc has longer, numerous and relatively uniform repeat motifs with lower serine content that assume tighter ß-crystals and denser packing, which are speculated to be responsible for its acclaimed properties of higher tensile strength and higher refractive index responsible for golden luster.

A comprehensive analysis of the chorion locus in silkmoth.

Despite more than 40 years of intense study, essential features of the silkmoth chorion (eggshell) are still not fully understood. To determine the precise structure of the chorion locus, we performed extensive EST analysis, constructed a bacterial artificial chromosome (BAC) contig, and obtained a continuous genomic sequence of 871,711 base pairs. We annotated 127 chorion genes in two segments interrupted by a 164 kb region with 5 non-chorion genes, orthologs of which were on chorion bearing scaffolds in 4 ditrysian families. Detailed transcriptome analysis revealed expression throughout choriogenesis of most chorion genes originally categorized as "middle", and evidence for diverse regulatory mechanisms including cis-elements, alternative splicing and promoter utilization, and antisense RNA. Phylogenetic analysis revealed multigene family associations and faster evolution of early chorion genes and transcriptionally active pseudogenes. Proteomics analysis identified 99 chorion proteins in the eggshell and micropyle localization of 1 early and 6 Hc chorion proteins.

Construction, complete sequence, and annotation of a BAC contig covering the silkworm chorion locus.

The silkmoth chorion was studied extensively by F.C. Kafatos' group for almost 40 years. However, the complete structure of the chorion locus was not obtained in the genome sequence of Bombyx mori published in 2008 due to repetitive sequences, resulting in gaps and an incomplete view of the locus. To obtain the complete sequence of the chorion locus, expressed sequence tags (ESTs) derived from follicular epithelium cells were used as probes to screen a bacterial artificial chromosome (BAC) library. Seven BACs were selected to construct a contig which covered the whole chorion locus. By Sanger sequencing, we successfully obtained complete sequences of the chorion locus spanning 871,711 base pairs on chromosome 2, where we annotated 127 chorion genes. The dataset reported here will recruit more researchers to revisit one of the oldest model systems which has been used to study developmentally regulated gene expression. It also provides insights into egg development and fertilization mechanisms and is relevant to applications related to improvements in breeding procedures and transgenesis.