Abstract
Peptidoglycans (PGNs) are major bacterial components recognized by the immune systems of insects and mammals. PGN recognition proteins (PGRPs) are widely distributed and highly conserved in vertebrates and invertebrates. PGRPs are a family of pattern recognition receptors that recognize peptidoglycan and regulate immune responses. In this study, we cloned two PGRP genes (BdPGRP-SA and BdPGRP-SD) from Bactrocera dorsalis (Hendel), which encode 192 and 196 amino acid residues, respectively. Both genes were highly expressed in adults, especially in the fat body and midgut. These two genes were up-regulated when challenged by the immune triggers, PGN-EB (Escherichia coli O111:B4) and PGN-SA (Staphylococcus aureus). The suppression of transcriptional expression of either gene by RNA interference (RNAi) resulted in increased sensitivities to Gram-negative E. coli and Gram-positive S. aureus PGNs. Suppression of BdPGRP-SA and -SD expression by RNAi resulted in weak expressions of four antimicrobial peptides (AMPs) upon injected with E. coli or S. aureus. BdPGRP-SA and -SD are involved in recognizing both Gram-negative and Gram-positive bacteria independently to activate the downstream AMP’s response to bacterial infection.
Highlights
Insects have an evolutionary conserved innate immune system that protects against pathogen infection [1,2]
The cDNA sequences of BdPGRP-SA and BdPGRP-SD were cloned from adult female B. dorsalis
We cloned the transcripts of BdPGRP-SA and BdPGRP-SD found in B. dorsalis
Summary
Insects have an evolutionary conserved innate immune system that protects against pathogen infection [1,2]. The humoral immune reaction is involved in the production of antimicrobial peptides (AMPs), which are mainly synthesized in the fat body and released into the hemolymph [3]. The expression of AMP genes is regulated by the Toll and immune deficiency (Imd) signal transduction pathways. The Toll pathway is activated by Gram-positive bacteria and fungi, while the Imd pathway is triggered by Gram-negative bacteria [4,5]. Microbial recognition represents the first step of the immune response. Innate immunity functions with receptors that recognize the conserved motifs of pathogens (peptidoglycan = PGN) but that are absent in the host [6]. PGN is recognized by conserved host PGN recognition proteins (PGRPs).
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