Structural and functional studies of pattern recognition receptors βGRP1 and βGRP2 in Sogatella furcifera

Beta-1,3-glucan recognition protein (βGRP) is an important pattern recognition receptor, which induces an immune response by recognizing and binding the pathogenic bacteria. In this study, we identified two βGRP genes in S. furcifera, βGRP1 and βGRP2. Both βGRP1 and βGRP2 proteins have a glycosyl hydrolases family 16 (GH16) domain  and a concanavalin A-like lectin/glucanase domain near the C-terminal. Quantitative polymerase chain reaction (qRT-PCR) analysis showed that the transcript levels of βGRP1 and βGRP2 in the fat body and gut were higher than those in other tissues. Furthermore, both were upregulated in response to challenges with Escherichia coli and Staphylococcus aureus. Recombinant βGRP1 and βGRP2 had a strong affinity for E. coli and S. aureus and caused bacteria to agglutinate. However, the results of the CCK-8 and bacteriostatic zone methods showed that recombinant βGRP1 and βGRP2 inhibited S. aureus but did not inhibit the growth of E. coli. Moreover, the silencing of βGRP1 or βGRP2 using dsRNA significantly downregulated the expression of the Toll pathway gene Dorsal after S. aureus challenge, while it did not affect the Imd pathway gene Relish.