Functional Analysis Of A Transmembrane Peptidoglycan Recognition Protein RfPGRP-L1 In The Maintainence Of Rhynchophorus Ferrugineus-gut Microbiota Symbiosis

Red palm weevil(RPW),Rhynchophorus ferrugineus Olivier,is a destructive invasive pest that seriously threats the biosafty of urban and coastal ecosystem in China.Recent studies have shown that there exists a large number of bacterial species in the intestine of RPW larva,and these bacterial species play some important roles in its nutrition metabolism,growth and development.RPW larva often lives in the environment containing huge quantity of different microbial species.Thus,RPW should discriminate pathogens quickly and effectively to maintain the homeostasis of the intestinal flora.Peptidoglycan recognition proteins(PGRPs)can recognize peptidoglycan(PGN),an important component of bacterial cell wall,to activate the insect immune responses.Therefore,PGRPs may play some key roles in the maintenance of the intestinal bacterial communities of insects.RfPGRP-L1 is a long transmembrane peptidoglycan recognition protein without conservative amidase sites.RT-qPCR revealed that RfPGRP-L1 mainly expressed in the foregut and hemolymph.The expression level of RfPGRP-L1 in fat body was significantly increased after the injection challenge of Staphylococcus aureus,indicating that RfPGRP-L1 might participate in the activation of systemic immunity.After feeding Escherichia coli,RfPGRP-L1 was significantly increased in gut,suggesting that RfPGRP-L1 might mediate RPW gut immunity.When RfPGRP-L1 was silenced,the expression level of antibacterial peptides,containing RfDefensin ? RfCecropin and RfAttacin,were significantly decreased.The ability of RPW larvae to clear the invaded eGFP-tagged E.coli was dramatically reduced.Additionally,the number of gut bacterial CFUs was significantly increased in RfPGRP-L1-silenced larvae.16 S rRNA high-throughout sequencing revealed that RfPGRP-L1 silencing caused some significant changes in community structure of RPW gut microbiota.Totally,our data suggest that RfPGRP-L1 can mediate the systemic immunity and gut immune responses by regulating the expression of the antimicrobial peptides and maintain the homeostasis of intestinal bacterial communities.