Abstract: 【Aim】 To explore the function of BmMCP18, a gut-specific metallocarboxypeptidase gene from Bombyx mori, and its resistance mechanism to exogenous virus infection. 【Methods】 The BmMCP18 knockout B. mori (BmMCP18KO)(C18KO) was constructed. The 5th instar larval midgut transcriptomes from C18KO and its control wild-type B. mori (C18KOC), and the 5th instar larval midgut transcriptomes of BmMCP18KO (C18KOV) infected with nuclear polyhedrosis virus (B. mori nuclear polyhedrosis virus, BmNPV) and its control wild-type B. mori (C18KOCV) were sequenced. The differentially expressed genes were analyzed for GO functional annotation and KEGG pathway enrichment, and qRT-PCR was used to verify the expression of related genes.【Results】 Compared with the control group C18KOC, C18KO had 75 genes with up-regulated expression and 303 genes with down-regulated expression. Compared with the control group C18KOCV, C18KOV had 96 genes with up-regulated expression and 57 genes with down-regulated expression. The significantly enriched GO items by differentially expressed genes in the C18KOC vs C18KO comparison group were extracellular space, cell surface, peptide cross-linking and synaptic target recognition. The most significantly enriched GO item by differentially expressed genes in the C18KOCV vs C18KOV comparison group was transmembrane transporter activity. The expression of genes related to the immune pathway, carbohydrate and energy metabolism pathway, including Toll and Imd pathway, and MAPK pathway in the transcriptome of the 5th instar larval midgut of C18KO, was significantly down-regulated，while that related to ubiquitin-mediated proteolysis pathway was significantly up-regulated, as compared with that of C18KOC. The expression of energy metabolism genes in the 5th instar larval midgut of C18KOV was significantly up-regulated as compared with that of C18KOCV. The qRT-PCR validation results indicated that the transcriptome data were reliable.【Conclusion】 The function of BmMCP18 involves cellular recognition, immune regulation and energy metabolism in the midgut of B. mori, possibly by participating in the immune response, energy and material supply of midgut cells to affect the resistance of B. mori to the infection of exogenous pathogens.

Key words: Bombyx mori, metallocarboxypeptidase gene, gene knockout; Bombyx mori nuclear polyhedrosis virus, midgut transcriptome