Peptidoglycan Recognition Protein (BmPGRP-l1) Is Involved In The Imd Pathway In The Silkworm,Bombyx Mori

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. 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 hours later, tissues were collected and used to detect the transcription levels of related transcription factors(Rel, Cactus and Relish) and antimicrobial peptides genes(AMPs)(Attacin, Moricin and Gloverin).Sequence analysis result of BmPGRP-L1 gene showed that there is high similarity between Drosophila DmPGRP-LC and BmPGRP-L1 of silkworm.Drosophila DmPGRP-LC activates Imd pathway after infection of Gram negative bacteria, is BmPGRP-L1 of silkworm involved in the Imd signaling pathway?In this study, microbial induction experiments suggested 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 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.The results of microbial induction experiments suggest that BmPGRP-L1 gene participates in the immune response of B. mori against gram negative bacteria E. coli,and the results of RNA interference experiments suggest that BmPGRP-L1 participates in the Imd signal transduction pathway in integument and head of B. Mori.And the results of this paper suggest that the BmPGRP-L1 gene plays an important role in the innate immunity of the silkworm.