An immune-responsive PGRP-S1 regulates the expression of antibacterial peptide genes in diamondback moth, Plutella xylostella (L.)

Peptidoglycan recognition proteins (PGRPs) are family of pattern recognition receptors (PRRs) and triggers the innate immune system (IIS) against the microbial infection. Although PGRPs have been intensively studied in model insects, they remain uncharacterized in most of the non-model insects. Here, we cloned and characterized a full-length cDNA of PGRP, from P. xylostella (PxPGRP-S1), which encodes a protein of 239 amino acids with PGRP domain, Ami2 domain and transmembrane region. The phylogenetic analysis revealed that the PxPGRP-S1 was closely related to the unigene of Plutella xylostella. Quantitative real-time PCR and immunohistochemistry revealed that PxPGRP-S1 is mainly expressed in the fat body of the healthy larva. The expression of PxPGRP-S1 was significantly upregulated in the midgut at 24 h postinfection by Bacillus thuringiensis. Silencing of the PxPGRP-S1 expression by RNAi, significantly decrease the expression of the antimicrobial peptides (AMPs) in the 4th instar larvae of P. xylostella. Similarly injection of an anti-PxPGRP-S1 serum caused the low expression of the AMPs in P. xylostella. Additionally, PxPGRP-S1 depleted P. xylostella by oral administration of bacterial expressed dsRNA decreased the resistance against B. thuringiensis challenge, leads to high mortality. Together, our result indicates that PxPGRP-S1, served as a bacterial pattern recognition receptor (PRR) and triggers the expression of AMPs in P. xylostella.