Very Early Corona Treatment-Mediated Artificial Incubation of Silkworm Eggs and Germline Transformation of Diapause Silkworm Strains.

Diapause is an important biological characteristic for many insect species to adapt to adverse environmental conditions and maintain the continuity of the race. Compared with the traditional hydrochloric acid or/and cold storage treatment methods, the artificial corona incubation technology of silkworm (Bombyx mori) eggs has many advantages including, the absence of pollution, easy operation and safety. However, this technology has not yet been applied in sericulture. In this study, we developed a novel artificial corona instrument to successfully disrupt the diapause of newly laid and refrigerated eggs from various Chinese and Japanese lineage silkworm strains. Subsequently, we invented a very early corona treatment (VECT) strategy to prevent the diapause of newly laid silkworm eggs within 4 h of oviposition. The hatching rates of the larvae were more than 95% in all diapause silkworm strains, which was comparable to the effect of the traditional HCl treatment strategy. In addition, we developed a combination strategy of VECT and pre-blastoderm microinjection and successfully created transgenic silkworms in various diapause strains. The results of the current study can aid in improving the corona artificial incubation technology and promote its application in sericulture.

A Microbiome Study Reveals Seasonal Variation in Endophytic Bacteria Among different Mulberry Cultivars.

Knowledge of seasonal shifts in the bacterial community composition among different mulberry (Morus L.) cultivars will facilitate to develop the biocontrol phytopathogens strategy using endophytic bacteria. The present study investigated the endophytic bacterial communities of four mulberry cultivars that have different resistance to mulberry fruit sclerotiniosis using Illumina-based sequencing of the 16S rRNA gene fragment in spring and autumn. The results indicated that spring samples harbor higher bacterial operational taxonomic units (OTUs), α-diversity, and bacterial community complexity in comparison with autumn samples. The taxonomic composition analysis showed that the majority of endophytes were composed of Proteobacteria (genus level: Methylobaterium) and Actinobacteria in spring, while sequences classified as Proteobacteria (genus level: Pantoea and Pseudomonas) were abundant in autumn. Analysis of ß-diversity also revealed endophytic bacteria were divided into two main groups by season. By comparison among different mulberry cultivars, we found that Pantoea, Methylobaterium, and Pseudomonas were the three major bacterial genera in all cultivars, while their relative abundances varied with cultivars and appeared no obvious relationship with resistance level of mulberry fruit sclerotiniosis. The complex correlation of the endophytic communities in susceptible mulberry cultivars was higher than that of the resistant cultivars. Overall, the findings suggested that season plays a key role in determining the mulberry endophytic bacterial communities, followed by host cultivar, and Proteobacteria was the predominant phylum in both seasons and different mulberry cultivars.

[Introduction trial of medicine mulberry (Morus nigra) in Chongqing].

Medicine mulberry (Morus nigra) mainly distributed in southern areas of Xinjiang Uighur Autonomous Region and introduced by grafting, is a unique Morus species, whose plant number is little. As a traditional herbal medicine, medicine mulberry with high levels of secondary metabolites has important values of scientific research and utilization. In order to solve the introduction problems for medicine mulberry, we have established its rapid propagation system through tissue culture since 2011. The shoots of medicine mulberry through tissue culture were transplanted into the field to carry out an introduction experiment. Here, we firstly reported that the growth status and pest and disease occurrence of medicine mulberry in the field of Chongqing and found that the medicine mulberry through tissue culture had well-developed root system, it showed better growth than medicine mulberry by grafting technique, and Pseudodendrothrips moil was a major pest of medicine mulberry. The introduction technique for medicine mulberry established successfully in this study could lay the foundation for large-scale cultivation and high efficiency utilization of medicine mulberry.

Mulberry Transcription Factor MnDREB4A Confers Tolerance to Multiple Abiotic Stresses in Transgenic Tobacco.

The dehydration responsive element binding (DREB) transcription factors have been reported to be involved in stress responses. Most studies have focused on DREB genes in subgroups A-1 and A-2 in herbaceous plants, but there have been few reports on the functions of DREBs from the A-3-A-6 subgroups and in woody plants. Moreover, mulberry trees are ecologically and economically important perennial woody plants, but there has been little research on its stress physiology, biochemistry and molecular biology. In this study, a DREB gene from the mulberry tree, designated as MnDREB4A, classified into the A-4 subgroup by our previous study, was selected for further characterization. Our results showed that the MnDREB4A protein was localized to the nucleus where it activated transcription. The promoter of MnDREB4A can direct prominent expression downstream of the ß-glucuronidase (GUS) gene under heat, cold, drought and salt stress, and GUS staining was deepest after 12 h of stress treatment. The MnDREB4A-overexpression transgenic tobacco showed the improved growth phenotype under untreated conditions, such as greener leaves, longer roots, and lower water loss and senescence rates. Overexpression of MnDREB4A in tobacco can significantly enhance tolerance to heat, cold, drought, and salt stresses in transgenic plants. The leaf discs and seedlings of transgenic plants reduced leaf wilting and senescence rates compared to the wild type plants under the different stress conditions. Further investigation showed that transgenic plants also had higher water contents and proline contents, and lower malondialdehyde contents under untreated condition and stress conditions. Our results indicate that the MnDREB4A protein plays an important role in plant stress tolerance.

[Progress of studies on medicinal fungus Phellinus].

The real sanghuang is a new species belonging to the Inonotus, which is commonly used for cancer treatment and human immune system improvement. This review summarized the progress on the studies of Phellinus Quel in recent years, including its taxonomy status, bioactive components, pharmacodynamics, separation and purification technologies. In addition, some related problems and perspectives were also discussed.

Mutation of a cuticular protein, BmorCPR2, alters larval body shape and adaptability in silkworm, Bombyx mori.

Cuticular proteins (CPs) are crucial components of the insect cuticle. Although numerous genes encoding cuticular proteins have been identified in known insect genomes to date, their functions in maintaining insect body shape and adaptability remain largely unknown. In the current study, positional cloning led to the identification of a gene encoding an RR1-type cuticular protein, BmorCPR2, highly expressed in larval chitin-rich tissues and at the mulberry leaf-eating stages, which is responsible for the silkworm stony mutant. In the Dazao-stony strain, the BmorCPR2 allele is a deletion mutation with significantly lower expression, compared to the wild-type Dazao strain. Dysfunctional BmorCPR2 in the stony mutant lost chitin binding ability, leading to reduced chitin content in larval cuticle, limitation of cuticle extension, abatement of cuticle tensile properties, and aberrant ratio between internodes and intersegmental folds. These variations induce a significant decrease in cuticle capacity to hold the growing internal organs in the larval development process, resulting in whole-body stiffness, tightness, and hardness, bulging intersegmental folds, and serious defects in larval adaptability. To our knowledge, this is the first study to report the corresponding phenotype of stony in insects caused by mutation of RR1-type cuticular protein. Our findings collectively shed light on the specific role of cuticular proteins in maintaining normal larval body shape and will aid in the development of pest control strategies for the management of Lepidoptera.

Identification and molecular characterization of a chitin deacetylase from Bombyx mori peritrophic membrane.

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. PM proteins are important determinants for PM structure and formation. In this study, the silkworm Bombyx mori midgut PM protein BmCDA7 was identified by proteomic tools. The full-length BmCDA7 cDNA is 1357 bp; the deduced protein is composed of 379 amino acid residues and includes a 16 amino acid residue signal peptide, a putative polysaccharide deacetylase-like domain and 15 cysteine residues present in three clusters. The heterologously expressed proteins of the BmCDA7 gene in yeast displayed chitin deacetylase activity. Expression of B. mori BmCDA7 was detected in the midgut at both the transcriptional and translational levels. The BmCDA7 gene was expressed by the newly hatched silkworm larvae until day seven of the fifth instar and was expressed at a high level in the newly exuviated larvae of different instars. The functions and regulatory mechanism of BmCDA7, however, need further investigation.

The molecular structures of major ampullate silk proteins of the wasp spider, Argiope bruennichi: a second blueprint for synthesizing de novo silk.

The dragline silk of orb-weaving spiders possesses extremely high tensile strength and elasticity. To date, full-length sequences of only two genes encoding major ampullate silk protein (MaSp) in Latrodectus hesperus have been determined. In order to further understand this gene family, we utilized in this study a variety of strategies to isolate full-length MaSp1 and MaSp2 cDNAs in the wasp spider Argiope bruennichi. A. bruennichi MaSp1 and MaSp2 are primarily composed of remarkably homogeneous ensemble repeats containing several complex motifs, and both have highly conserved C-termini and N-termini. Two novel amino acid motifs, GGF and SGR, were found in MaSp1 and MaSp2, respectively. Amino acid composition analysis of silk, luminal contents and predicted sequences indicates that MaSp1 and MaSp2 are two major components of major ampullate glands and that the ratio of MaSp1 to MaSp2 is approximately 3:2 in dragline silk. Furthermore, both the MaSp1:MaSp2 ratio and the conserved termini are closely linked with the production of high quality synthetic fibers. Our results make an important contribution to our understanding of major ampullate silk protein structure and provide a second blueprint for creating new composite silk which mimics natural spider dragline silk.

Expansion of the silkworm GMC oxidoreductase genes is associated with immunity.

The glucose-methanol-choline (GMC) oxidoreductases constitute a large gene family in insects. Some of these enzymes play roles in developmental or physiological process, such as ecdysteroid metabolism. However, little is known about the functional diversity of the insect GMC family. Here, we identified 43 GMC genes in the silkworm genome, the largest number of GMC genes among all the insect genomes sequenced to date. Similar to the other insects, there is a highly conserved GMC cluster within the second intron of the silkworm flotillin-2 (flo-2) gene. However, the silkworm GMC genes outside of the conserved GMC cluster have experienced a large expansion. Phylogenetic analysis suggested that the silkworm GMCß subfamily contained 22 copies and made a major contribution to expansion of the silkworm GMC genes. Eighteen of the 22 members of the silkworm GMCß subfamily are located outside of the conserved GMC cluster, and are known as silkworm expansion genes (SEs). Relative-rate tests showed that SEs evolved significantly faster than the GMCß genes inside the conserved GMC cluster. Accordingly, the third position GC content (GC3s) and codon bias of SEs are significantly different from those of the GMCß genes in the conserved GMC cluster. The elevated evolutionary rate of the silkworm GMCß genes outside of the conserved GMC cluster may reflect the evolution of function diversity. At least 24 of the 43 silkworm GMC genes were differently transcribed and expressed in a tissue- or stage-specific manner during the larval stage. Strikingly, microarray data revealed that four different pathogens upregulated most of the silkworm GMCß genes. Furthermore, RNA interference of representative upregulated GMCß genes reduced the survival rate of the silkworm when infected by pathogens. Taken together, the results suggested that expansion of the silkworm GMC oxidoreductase genes is associated with immunity.

[Computational approaches for identification and classification of transposable elements in eukaryotic genomes].

Repetitive sequences (repeats) represent a significant fraction of the eukaryotic genomes and can be divided into tandem repeats, segmental duplications, and interspersed repeats on the basis of their sequence characteristics and how they are formed. Most interspersed repeats are derived from transposable elements (TEs). Eukaryotic TEs have been subdivided into two major classes according to the intermediate they use to move. The transposition and amplification of TEs have a great impact on the evolution of genes and the stability of genomes. However, identification and classification of TEs are complex and difficult due to the fact that their structure and classification are complex and diverse compared with those of other types of repeats. Here, we briefly introduced the function and classification of TEs, and summarized three different steps for identification, classification and annotation of TEs in eukaryotic genomes: (1) assembly of a repeat library, (2) repeat correction and classification, and (3) genome annotation. The existing computational approaches for each step were summarized and the advantages and disadvantages of the approaches were also highlighted in this review. To accurately identify, classify, and annotate the TEs in eukaryotic genomes requires combined methods. This review provides useful information for biologists who are not familiar with these approaches to find their way through the forest of programs.

FLP recombinase-mediated site-specific recombination in silkworm, Bombyx mori.

A comprehensive understanding of gene function and the production of site-specific genetically modified mutants are two major goals of genetic engineering in the post-genomic era. Although site-specific recombination systems have been powerful tools for genome manipulation of many organisms, they have not yet been established for use in the manipulation of the silkworm Bombyx mori genome. In this study, we achieved site-specific excision of a target gene at predefined chromosomal sites in the silkworm using a FLP/FRT site-specific recombination system. We first constructed two stable transgenic target silkworm strains that both contain a single copy of the transgene construct comprising a target gene expression cassette flanked by FRT sites. Using pre-blastoderm microinjection of a FLP recombinase helper expression vector, 32 G3 site-specific recombinant transgenic individuals were isolated from five of 143 broods. The average frequency of FLP recombinase-mediated site-specific excision in the two target strains genome was approximately 3.5%. This study shows that it is feasible to achieve site-specific recombination in silkworms using the FLP/FRT system. We conclude that the FLP/FRT system is a useful tool for genome manipulation in the silkworm. Furthermore, this is the first reported use of the FLP/FRT system for the genetic manipulation of a lepidopteran genome and thus provides a useful reference for the establishment of genome manipulation technologies in other lepidopteran species.

[Progress in Cre/lox site-specific recombination system in higher eukaryotes].

Cre/lox system derived from P1 bacteriaphage can quickly and effectively achieve gene insertion, deletion, replacement, and inversion by means of site-specific recombination. As one of the most important tools for gene targeting at present, Cre/lox system has been widely used in Arabidopsis thaliana, Oryza sativa L., Mus musculus, Drosophila melanogaster, Danio rerio, and other higher eukaryotic organisms. This review roundly described the basic profile of Cre/lox system, and its application in higher eukaryotes. In addition, we also discussed the main problems and developmental trend of the Cre/lox system in this review, which can be a good reference for using Cre/lox system to realize the gene manipulations of the different high eukaryotic organisms.

Molecular cloning and characterization of Ecdysone oxidase and 3-dehydroecdysone-3α-reductase involved in the ecdysone inactivation pathway of silkworm, Bombyx mori.

Molting hormone (ecdysteroid) is one of the most important hormones in insects. The synthesis and inactivation of the ecdysteroid regulate the developmental process of insects. A major pathway of ecdysone inactivation is that ecdysone is converted to 3-dehydroecdysone, and then further to 3-epiecdysone in insects. Two enzymes (ecdysone oxidase: EO and 3DE-3α-reductase) participate in this pathway. In this study, based on the previously characterized cDNAs in Spodoptera littoralis, we cloned and characterized EO and 3DE-3α-reductase genes in the silkworm, Bombyx mori. The heterologously expressed proteins of the two genes in yeast showed the ecdysone oxidase and 3DE-3α-reductase activities, respectively. Expression of BmEO was only detected in the midgut at transcriptional and translational levels. We also localized EO within the midgut goblet cell cavities. For Bm3DE-3α-reductase gene, RT-PCR and western blot showed that it was expressed in the midgut and the Malpighian tubules. Moreover, we localized 3DE-3α-reductase within the midgut goblet cell cavities and the cytosol of principal cells of the Malpighian tubules. These two genes have similar expression profiles during different developmental stages. Both genes were highly expressed at the beginning of the 5th instar, and remained a relative low level during the feeding stage, and then were highly expressed at the wandering stage. All these results showed that the profiles of the two genes were well correlated with the ecdysteroid titer. The functional characterization of the enzymes participating in ecdysone inactivation in the silkworm provides hints for the artificial regulation of the silkworm development and biological control of pests.

Pathogen-origin horizontally transferred genes contribute to the evolution of Lepidopteran insects.

BACKGROUND: Horizontal gene transfer (HGT), a source of genetic variation, is generally considered to facilitate hosts' adaptability to environments. However, convincing evidence supporting the significant contribution of the transferred genes to the evolution of metazoan recipients is rare. RESULTS: In this study, based on sequence data accumulated to date, we used a unified method consisting of similarity search and phylogenetic analysis to detect horizontally transferred genes (HTGs) between prokaryotes and five insect species including Drosophila melanogaster, Anopheles gambiae, Bombyx mori, Tribolium castaneum and Apis mellifera. Unexpectedly, the candidate HTGs were not detected in D. melanogaster, An. gambiae and T. castaneum, and 79 genes in Ap. mellifera sieved by the same method were considered as contamination based on other information. Consequently, 14 types of 22 HTGs were detected only in the silkworm. Additionally, 13 types of the detected silkworm HTGs share homologous sequences in species of other Lepidopteran superfamilies, suggesting that the majority of these HTGs were derived from ancient transfer events before the radiation of Ditrysia clade. On the basis of phylogenetic topologies and BLAST search results, donor bacteria of these genes were inferred, respectively. At least half of the predicted donor organisms may be entomopathogenic bacteria. The predicted biochemical functions of these genes include four categories: glycosyl hydrolase family, oxidoreductase family, amino acid metabolism, and others. CONCLUSIONS: The products of HTGs detected in this study may take part in comprehensive physiological metabolism. These genes potentially contributed to functional innovation and adaptability of Lepidopteran hosts in their ancient lineages associated with the diversification of angiosperms. Importantly, our results imply that pathogens may be advantageous to the subsistence and prosperity of hosts through effective HGT events at a large evolutionary scale.

Topological and functional characterization of an insect gustatory receptor.

Insect gustatory receptors are predicted to have a seven-transmembrane structure and are distantly related to insect olfactory receptors, which have an inverted topology compared with G-protein coupled receptors, including mammalian olfactory receptors. In contrast, the topology of insect gustatory receptors remains unknown. Except for a few examples from Drosophila, the specificity of individual insect gustatory receptors is also unknown. In this study, the total number of identified gustatory receptors in Bombyx mori was expanded from 65 to 69. BmGr8, a silkmoth gustatory receptor from the sugar receptor subfamily, was expressed in insect cells. Membrane topology studies on BmGr8 indicate that, like insect olfactory receptors, it has an inverted topology relative to G protein-coupled receptors. An orphan GR from the bitter receptor family, BmGr53, yielded similar results. We infer, from the finding that two distantly related BmGrs have an intracellular N-terminus and an odd number of transmembrane spans, that this is likely to be a general topology for all insect gustatory receptors. We also show that BmGr8 functions independently in Sf9 cells and responds in a concentration-dependent manner to the polyalcohols myo-inositol and epi-inositol but not to a range of mono- and di-saccharides. BmGr8 is the first chemoreceptor shown to respond specifically to inositol, an important or essential nutrient for some Lepidoptera. The selectivity of BmGr8 responses is consistent with the known responses of one of the gustatory receptor neurons in the lateral styloconic sensilla of B. mori, which responds to myo-inositol and epi-inositol but not to allo-inositol.

Genome-wide analysis of cytochrome P450 monooxygenase genes in the silkworm, Bombyx mori.

Based on the advances in the silkworm genome project, a new genome-wide analysis of cytochrome P450 genes was performed. A total of 84 CYP-related sequences were identified and could be classified into 26 families and 47 subfamilies according to standard nomenclature. Seventy eight of the eighty four genes appear to be functional and six are probable pseudogenes. The distribution of Bombyx mori P450s in the genome shows that most of them are tandem arranged on chromosomes, only 34 genes are present as singletons, with 8 clusters including 3 or more than 3 genes. Sequence alignments were used to reconstruct phylogenetic trees and to analyze the intron-exon organizations of the functional genes. The conserved intron positioning agrees perfectly with their common grouping on the tree. The presence of three extremely ancient introns which are conserved across different clans indicates that a few introns are still highly conserved after they have undergone extensive evolutionary changes of B. mori P450 duplication and divergence. Comparison of the P450s from B. mori to the P450s from Drosophila melanogaster shows that the expansion is not uniform across the gene families. Remarkably, two mitochondrial families, the B. mori CYP333 and D. melanogaster Cyp12, formed two orthologous groups in the phylogenetic tree. All CYP333s can be proposed to be related to xenobiotic metabolism in accordance with the D. melanogaster Cyp12s. The characterization and evolutionary analysis of P450s from B. mori in the current study provide useful information for understanding the characteristics and diversity of P450s from B. mori and the baseline for functional analyses of individual P450s in this model Lepidopteran insect.

Evidence of selection at melanin synthesis pathway loci during silkworm domestication.

The domesticated silkworm (Bombyx mori) was domesticated from wild silkworm (Bombyx mandarina) more than 5,000 years ago. During domestication, body color between B. mandarina and B. mori changed dramatically. However, the molecular mechanism of the silkworm body color transition is not known. In the present study, we examined within- and between-species nucleotide diversity for eight silkworm melanin synthesis pathway genes, which play a key role in cuticular pigmentation of insects. Our results showed that the genetic diversity of B. mori was significantly lower than that of B. mandarina and 40.7% of the genetic diversity of wild silkworm was lost in domesticated silkworm. We also examined whether position effect exists among melanin synthesis pathway genes in B. mandarina and B. mori. We found that the upstream genes have significantly lower levels of genetic diversity than the downstream genes, supporting a functional constraint hypothesis (FCH) of metabolic pathway, that is, upstream enzymes are under greater selective constraint than downstream enzymes because upstream enzymes participate in biosynthesis of a number of metabolites. We also investigated whether some of the melanin synthesis pathway genes experienced selection during domestication. Neutrality test, coalescent simulation, as well as network and phylogenetic analyses showed that tyrosine hydroxylase (TH) gene was a domestication locus. Sequence analysis further suggested that a putative expression enhancer (Abd-B-binding site) in the intron of TH gene might be disrupted during domestication. TH is the rate-limiting enzyme of melanin synthesis pathway in insects. Real-time polymerase chain reaction assay did show that the relative expression levels of TH gene in B. mori were significantly lower than that in B. mandarina at three different developmental stages, which is consistent with light body color of domesticated silkworm relative to wild silkworm. Therefore, we speculated that expression change of TH gene may contribute to the body color transition from B. mandarina to B. mori. Our results emphasize the exceptional role of gene expression regulation in morphological transition of domesticated animals.

Nucleotide diversity and selection signature in the domesticated silkworm, Bombyx mori, and wild silkworm, Bombyx mandarina.

To investigate the patterns of nucleotide diversity in domesticated silkworm, Bombyx mori L. (Lepidoptera: Bombycidae) and its wild relative, Chinese wild silkworm, Bombyx mandarina Moore, we sequenced nine nuclear genes. Neutrality test and coalescent simulation for these genes were performed to look at bottleneck intensity and selection signature; linkage disequilibrium (LD) within and between loci was employed to investigate allele association. As a result, B. mori lost 33-49% of nucleotide diversity relative to wild silkworm, which is similar to the loss levels found in major cultivated crops. Diversity of B. mori is significantly lower than that of B. mandarina measured as π(total) (0.01166 vs. 0.1741) or θ(W)(0.01124 vs. 0.02206). Bottleneck intensity of domesticated silkworm is 1.5 (in terms of k = N(b) /d, N(b) -bottleneck population size; d-bottleneck duration) with different durations. Gene DefA showed signature of artificial selection by all analysis methods and might experience strong artificial selection in B. mori during domestication. For nine loci, both curves of LD decay rapidly within 200 bp and drop slowly when distance is > 200 bp, although that of B. mori decays slower than B. mandarina at loci investigated. However, LD could not be estimated at DefA in B. mori and at ER in both silkworms. Elevated LD observed in B. mori may be indicator of selection and demographic events.

Comparative genetic diversity and genetic structure of three chinese silkworm species Bombyx mori L. (Lepidoptera: Bombycidae), Antheraea pernyi Guérin-Meneville and Samia cynthia ricini donovan (Lepidoptera: Saturniidae)

The genetic diversity and genetic structure of three Chinese silkworm species Bombyx mori L., Antheraea pernyi Guérin-Meneville and Samia cynthia ricini Donovan were comparatively assessed based on RAPD markers. At the species level, A. pernyi and B. mori showed high levels of genetic diversity, whereas S. cynthia ricini showed low level of genetic diversity. However, at the strain level, A. pernyi had relatively highest genetic diversity and B. mori had lowest genetic diversity. Analysis of molecular variance (AMOVA) suggested that 60 percent and 72 percent of genetic variation resided within strains in A. pernyi and S. cynthia ricini, respectively, whereas only 16 percent of genetic variation occurred within strains in B. mori. In UPGMA dendrogram, individuals of A. pernyi and B. mori formed the strain-specific genetic clades, whereas those of S. cynthia ricini were distributed in a mixed way. The implications of these results for the conservation and utilization in breeding programs of three silkworm species are discussed.

Burst expansion, distribution and diversification of MITEs in the silkworm genome.

BACKGROUND: Miniature inverted-repeat transposable elements (MITEs) are widespread in plants and animals. Although silkworm (Bombyx mori) has a large amount of and a variety of transposable elements, the genome-wide information of the silkworm MITEs is unknown. RESULTS: We used structure-based and homology approaches to search for MITEs in the silkworm genome. We identified 17 MITE families with a total of 5785 members, accounting for ~0.4% of the genome. 7 of 17 MITE families are completely novel based on the nucleotide composition of target site duplication (TSD) and/or terminal inverted repeats (TIR). Silkworm MITEs were widely and nonrandom distributed in the genome. One family named BmMITE-2 might experience a recent burst expansion. Network and diversity analyses for each family revealed different diversification patterns of the silkworm MITEs, reflecting the signatures of genome-shocks that silkworm experienced. Most silkworm MITEs preferentially inserted into or near genes and BmMITE-11 that encodes a germline-restricted small RNA might silence its the closest genes in silkworm ovary through a small RNA pathway. CONCLUSIONS: Silkworm harbors 17 MITE families. The silkworm MITEs preferred to reside in or near genes and one MITE might be involved in gene silence. Our results emphasize the exceptional role of MITEs in transcriptional regulation of genes and have general implications to understand interaction between MITEs and their host genome.