Abstract: 【Aim】 This study aims to investigate the expression patterns of the peptidoglycan recognition protein gene ApPGRP in the desert beetle Anatolica polita, its regulation of the downstream immune-related genes in vivo and the binding capability of the recombinant protein ApPGRP with bacteria in vitro. 【Methods】 The expression vector pET-28a-ApPGRP was constructed and transformed into Escherichia coli BL21 (DE3). The recombinant protein His-ApPGRP was expressed and purified, and its binding capabilities with Staphylococcus aureus and peptidoglycan (PGN) were detected, respectively. The expression levels of immune-related genes including ApPGRP, antimicrobial peptide genes ApAttacin2 and ApAttacin1, defensin gene ApDefensin, serine protease gene ApSP and serine protease inhibitor gene ApSerpin in the 6th instar larva of A. polita infected by S. aureus were determined by qRT-PCR. The expression levels of the immune-related genes in the 6th instar larvae of A. polita after RNAi of ApPGRP and S. aureus stimulation following RNAi of ApPGRP were also detected by qRT-PCR, respectively. 【Results】 The purified recombinant protein His-ApPGRP had the binding capability with both S. aureus and PGN. Except for ApSP, the expression of the other tested immune-related genes in the 6th instar larva of A. polita was significantly up-regulated after S. aureus injection. When ApPGRP was knocked down by RNAi, the expression of all the other tested immune-related genes in the 6th instar larva of A. polita was significantly downregulated and the expression levels of these genes in response to subsequent S. aureus challenge in the RNAi-treated larva were also significantly lower than those of the control group. 【Conclusion】 These results show that ApPGRP plays an important role in recognizing exogenous microorganisms, activating signaling pathways and regulating the expression of antimicrobial peptides in the immune defense of A. polita.

Key words: Anatolica polita; peptidoglycan recognition proteins, prokaryotic expression, Staphylococcus aureus, peptidoglycan, RNAi