Transcriptome analysis of differentially expressed genes involved in innate immunity following Bacillus thuringiensis challenge in Bombyx mori larvae

In this study, we describe RNA-seq expression profiling of larval Bombyx mori response to hemocoel injection of Bacillus thuringiensis (Bt). Two transcriptomes were generated from the hemocytes of the PBS- and Bt-injected B. mori larvae. More than 49 million 100-bp paired-end reads, encompassing over 7.3 Gb of sequence data, were generated for each library. After filtering the raw reads and removing the rRNA mapped reads, more than 89% of the reads in each library could be mapped to the silkworm genome reference sequence. Comparison of gene expression levels revealed that a total of 133 unigenes were upregulated while 84 unigenes were downregulated in PBS vs Bt. To further investigate the biological functions of different expression genes (DEGs), gene ontology (GO) and functional enrichment analysis were performed to map all the DEGs to terms in the GO, euKaryotic Ortholog Groups of proteins (KOG) and Kyoto Encyclopedia of Genes and Genomes Pathway (KEGG) database. Among these DEGs, many genes involved in immunity against Bt challenge were identified. These included genes participated in pattern recognition, antimicrobial peptides, insecticide resistance or detoxification, immune melanization, cytoskeleton reorganization and many other immune effectors. To confirm the gene expression patterns identified by the RNA-seq data, the transcript levels of 10 immune related DEGs were examined by quantitative real-time PCR (qRT-PCR). The results showed that the DEGs obtained from the deep sequencing data were accurate and gene expression profiles from RNA-Seq data were reliable. Our studies provide insights into the to immune response of B. mori underling the stress of Bt, which is valuable to understand how Bt affects the innate immune system of silkworm and provide new approaches to control insect pests by using Bt as a biological insecticide.