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Background: Pseudogenes are sequences that have lost the ability to transcribe RNA molecules or encode truncated but possibly functional proteins. While they were once considered to be meaningless remnants of evolution, recent researches have shown that pseudogenes play important roles in various biological processes. However, the studies of pseudogenes in the silkworm, an important model organism, are limited and have focused on single or only a few specific genes. Objective: To fill these gaps, we present a systematic genome-wide studies of pseudogenes in the silkworm. Methods: We identified the pseudogenes in the silkworm using the silkworm genome assemblies, transcriptome, protein sequences from silkworm and its related species. Then we used transcriptome datasets from 832 RNA-seq analyses to construct spatio-temporal expression profiles for these pseudogenes. Additionally, we identified tissue-specifically expressed and differentially expressed pseudogenes to further understand their characteristics. Finally, the functional roles of pseudogenes as lncRNAs were systematically analyzed. Results: We identified a total of 4410 pseudogenes, which were grouped into 4 groups, including duplications (DUPs), unitary pseudogenes (Unitary), processed pseudogenes (retropseudogenes, RETs), and fragments (FRAGs). The most of pseudogenes in the domestic silkworm were generated before the divergence of wild and domestic silkworm, however, the domestication may also involve in the accumulation of pseudogenes. These pseudogenes were clearly divided into 2 cluster, a highly expressed and a lowly expressed, and the posterior silk gland was the tissue with the most tissue-specific pseudogenes (199), implying these pseudogenes may be involved in the development and function of silkgland. We identified 3299 lncRNAs in these pseudogenes, and the target genes of these lncRNAs in silkworm pseudogenes were enriched in the egg formation and olfactory function. Conclusions: This study replenishes the genome annotations for silkworm, provide valuable insights into the biological roles of pseudogenes. It will also contribute to our understanding of the complex gene regulatory networks in the silkworm and will potentially have implications for other organisms as well. [ABSTRACT FROM AUTHOR]

Wild ( Bombyx mandarina) and domestic silkworms ( B. mori ) are good models for investigating insect domestication, as 5000 years of artificial breeding and selection have resulted in significant differences between B. mandarina and B. mori . In this study, we improved the genome assemblies to the chromosome level and updated the protein-coding gene annotations for B. mandarina . Based on this updated genome, we identified 68 cytochrome P450 genes in B. mandarina . The cytochrome P450 repository in B. mandarina is smaller than in B. mori . Certain currently unknown key genes, rather than gene number, are critical for insecticide resistance in B. mandarina, which shows greater resistance to insecticides than B. mori . Based on the physical maps of B. mandarina, we located 66 cytochrome P450s on 18 different chromosomes, and 27 of the cytochrome P450 genes were concentrated into seven clusters. KEGG enrichment analysis of the P450 genes revealed the involvement of cytochrome P450 genes in hormone biosynthesis. Analyses of the silk gland transcriptome identified candidate cytochrome P450 genes ( CYP306A ) involved in ecdysteroidogenesis and insecticide metabolism in B. mandarina ., Competing Interests: Cao Deng is employed by Genefang and DNA Stories Bioinformatics Center. The members of Genefang Research Team are employed by Genefang. The authors declare there are no competing interests., (©2021 Wan et al.)