Comparative Analysis of PGRP Family in Polymorphic Worker Castes of Solenopsis invicta

Peptidoglycan recognition proteins (PGRPs) are a class of pattern recognition receptors (PRRs) that activate the innate immune system in response to microbial infection by detection of peptidoglycan, a distinct component of bacterial cell walls. Bioinformatic studies have revealed four PGRPs in the red imported fire ant <i>Solenopsis invicta</i>; nonetheless, the mechanism of the immune response of <i>S. invicta</i> induced by pathogens is still poorly understood. The peptidoglycan recognition protein full-length cDNA (designated as <i>SiPGRP</i>-<i>S1/S2/S3/L</i>) from <i>S. invicta</i> was used in this investigation. According to the sequencing analysis, there was a significant degree of homology between the anticipated amino acid sequence of SiPGRPs and other members of the PGRPs superfamily. Molecular docking studies demonstrated that SiPGRPs show strong binding affinity for a variety of PGN substrates. Additionally, tissue distribution analysis indicated that <i>SiPGRPs</i> are primarily expressed in several tissues of naïve larvae, including fat body, hemocytes, head, and thorax, as detected by quantitative real-time PCR (RT-qPCR). Microbial challenges resulted in variable changes in mRNA levels across different tissues. Furthermore, the antibacterial effects of antimicrobial peptides (AMPs) produced by major ants infected with <i>Metarhizium anisopliae</i> were assessed. These AMPs demonstrated inhibitory effects against <i>M. anisopliae</i>, <i>Staphylococcus aureus</i>, and <i>Escherichia coli</i>, with the most pronounced effect observed against <i>E. coli</i>. In conclusion, SiPGRPs act as pattern recognition receptors (PRRs) that identify pathogens and initiate the expression of AMPs in <i>S. invicta</i>, this mechanism contributes to the development of biopesticides designed for the targeted control of invasive agricultural pests.