ß-1,3-Glucan recognition protein 3 activates the prophenoloxidase system in response to bacterial infection in Ostrinia furnacalis Guenée.

ABSTRACT

Pattern recognition receptors (PRRs) are biosensor proteins that bind to non-self pathogen associated molecular patterns (PAMPs). ß-1,3-glucan recognition proteins (ßGRPs) play an essential role in immune recognition and signaling pathway of insect innate immunity. Here, we report the cloning and characterization of cDNA of OfßGRP3 from Ostrinia furnacalis larvae. The OfßGRP3 contains 1455 bp open reading frame, encoding a predicted 484 amino acid residue protein. In hemocytes, the expression levels of OfßGRP3 in Escherichia coli-challenged group were higher than those of Bacillus subtilis-challenged group at 2, 4, 8, 10 and 12 h post injection (HPI). In fat body, OfßGRP3 expression in both B. subtilis and E. coli-challenged group was significantly higher than that in untreated group from 4 to 10 HPI, and then the expression continuously dropped from 12 to 36 HPI. The OfßGRP3 expression in laminarin-injected group was higher than that in lipopolysaccharides (LPS)-injected group in various test tissues from 4 to 24 HPI. The LT50 of E. coli-infected OfßGRP3-RNAi larvae (1.0 days) was significantly lower compared with that of E. coli infected wild-type larvae (3.0 days) (p < 0.01). Only 10.2% Sephadex G50 beads (degree 3) were completely melanized in the larvae inoculated with OfßGRP3 dsRNA, as compared to 48.8% in control larvae (p < 0.01). A notable reduction in the PO activity and IEARase activity in hemolymph was also detected in the OfßGRP3 knockdown larvae. Our study demonstrates that OfßGRP3 is one of PRR members involved the PPO-activating system in O. furnacalis larvae.