| Red palm weevil(RPW),Rhynchophorus ferrugineus Olivier,is a destructive alien stem-boring insect pest for palm trees in China.Previous evidence confirmed that RPW has established the symbiotic interactions with its intestinal microbiota which profoundly affect its physiological traits.However,it is still unknown how RPW maintain an immune balance between tolerating a beneficial microbiome and protecting against enterophathogens.Peptidoglycan recognition proteins(PGRPs)are a family of immune regulators that conserved from insects to mammals.Here,we show that RPW PGRP-S1 is a secreted protein with amidase activity which can degrade bacteria-derived peptidoglycan(PGN).RT-qPCR showed that the expression of RfPGRP-S1 in gut was significantly higher than those in other tissues.The expression of RfPGRP-S1 could be significantly induced by bacteria challenge.These results suggest that RfPGRP-S1 may be involved in RPW immune response.In vitro functional assays revealed that rRfPGRP-S1 caused significant agglutination of E.coli and S.aureus,and the addition of Zn2+caused stronger bacteria agglutination.Moreover,rRfPGRP-S 1 obviously inhibited the growth of S.aureus.These results indicate that RfPGRP-S1 is a pathogen recognition receptor with bactericidal activity.RfPGRP-S1 knockdown reduced the persistence of E.coli in gut,hemolymph and load of indigenous gut microbiota significantly.Furthermore,ANOSIM analysisuncovered RfPGRP-S1 knockdown intensively altered the community structure of RPW gut microbiota.Higher levels of the antimicrobial peptide,Defensin,were detected in guts of RfPGRP-Sl silenced larvae than controls.Collectively,our data demonstrated that RfPGRP-S1 do not only prevent excessive activation of intestinal immunity by degrading peptidoglycan to maintain the healthy homeostasis of intestinal flora,but also as a bactericidal effector to control proliferation of commensals and persistence of noncommensals. |
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