Abstract: 【Aim】 Peptidoglycan recognition proteins (PGRPs) are one kind of important pattern recognition proteins in insect immune system. In this study, we aim to investigate the expression patterns of PGRP-SA from Plutella xylostella (designated as PxPGRP-SA) and its involvement in the regulation of the expression of antimicrobial peptide genes in P. xylostella after infection by Bacillus thuringiensis. 【Methods】 The transcription pattern of PxPGRP-SA in P. xylostella larvae infected by B. thuringiensis was analyzed by quantitative real-time reverse transcription PCR (qRT-PCR), and the regulation of the expression of antimicrobial peptide genes by PxPGRP-SA in P. xylostella was investigated by RNAi technology and antiserum blocking assay. 【Results】 qRT-PCR analysis revealed that the transcripts of PxPGRP-SA increased significantly at 6 h after injection of live B. thuringiensis into the fat body and hemocytes of the 4th instar larvae of P. xylostella, with the highest expression level at 24 h in fat body and 18 h in hemocytes, respectively. The transcript of PxPGRP-SA in the 4th instar larvae of P. xylostella decreased due to RNAi. Blocking down the transcript of PxPGRP-SA by RNAi also reduced the transcriptional levels of four antibacterial peptide genes including cecropin, moricin-2, lysozyme and defensin in the 4th instar larvae and the mRNA levels of Dorsal and Sp?tzle genes significantly. Blocking the activity of PxPGRP-SA by injection of anti-PxPGRP-SA serum into the 4th instar larvae of P. xylostella also decreased the transcription levels of antibacterial peptide genes in the fat body rapidly. Silence of the expression of PxPGRP-SA decreased the survival rate of P. xylostella larvae feeding live B. thuringiensis significantly. 【Conclusion】 PxPGRP-SA is involved in regulating the expression of downstream antibacterial peptide genes including cecropin, moricin-2, lysozyme and defensin in P. xylostella, and plays an important role in the immune defense of P. xylostella against B. thuringiensis infection.  

Key words: Plutella xylostella, peptidoglycan recognition protein, RNAi, antiserum, antimicrobial peptides