Abstract: 【Aim】 As an important pattern recognition receptor, peptidoglycan recognition protein (PGRP) plays an important role in the innate immunity of the silkworm, Bombyx mori. The study aims to identify and characterize a new PGRP gene PGRP-L1 from Bombyx mori, analyze its immune function and the immune signaling pathway that the gene is involved in. 【Methods】 We successfully cloned the gene BmPGRP-L1 from Bombyx mori by RT-PCR. Newly-exuviated 5th instar larvae of B. mori were injected with Escherichia coli, Saccharomyces cerevisiae, Bacillus subtilis and phosphate buffered saline, respectively. After 12 h, the integument and head were collected and used for RNA extraction. RT-PCR and gel electrophoresis were then performed to measure the transcriptional level of BmPGRP-L1 gene. Newly-exuviated 5th instar larvae were injected with dsRNA specific for BmPGRP-L1 and PBS, respectively, then 6 h later injected with the inactivated three microorganisms and phosphate buffered saline, and another 6 h later, tissues were collected and used to detect the transcription levels of related transcription factors (Rel, Cactus and Relish) and antimicrobial peptides (AMPs) genes (Attacin, Moricin and Gloverin). 【Results】 Microbial induction experiments showed that BmPGRP-L1 mRNA level was upregulated in the integument and head of B. mori 12 h after injection of E. coli but presented no change after injection of S. cerevisiae or B. subtilis. RNA interference experiments showed that the expression level of BmPGRP-L1 was successfully knocked down, and the expression level of relish in the newly-exuviated 5th instar larvae subjected to BmPGRP-L1 RNAi was significantly lower than the normal control post E. coli challenge, and the corresponding expression levels of the relevant antimicrobial peptide genes were downregulated to different degrees. 【Conclusion】 The results suggest that BmPGRP-L1 gene participates in the immune response of B. mori against gram negative bacteria E. coli, and BmPGRP-L1 participates in the Imd signal transduction pathway in integument and head of B. mori.

Key words: Bombyx mori, innate immunity, peptidoglycan recognition protein, microbial invasion, RNA interference