A C-type lectin with dual-CRD from Tribolium castaneum is induced in response to bacterial challenge.

BACKGROUND C-type lectins (CTLs), a group of pattern recognition receptors, are involved in regulating the immune response of insects and could be used as potential targets for pest control. However, information about roles of CTLs in the innate immunity ofTribolium castaneum, a serious, worldwide pest that damages stored grain products, is relatively scarce. RESULTS Here, a CTL with dual carbohydrate recognition domains (CRDs) containing a highly conserved WHD (Trp(53)-His(54)-Asp(55)) motif was identified inT. castaneumand named as TcCTL3. Spatiotemporal analysis showed thatTcCTL3was highly expressed in all developmental stages except early eggs, and mainly distributed in central nervous system and hemolymph. The transcript levels ofTcCTL3were significantly increased after lipopolysaccharide (LPS) and peptidoglycan (PGN) stimulation. Recombinant TcCTL3 was able to bind directly to LPS, PGN and all tested bacteria and induce a broad spectrum of microbial agglutination in the presence of Ca2+. The binding was shown mainly through CRD1 domain of TcCTL3. WhenTcCTL3was knocked down by RNA interference, expression of nine antimicrobial peptides (AMPs) (attacin1,attacin2,attacin3,defensins1,defensins2,coleoptericin1,coleoptericin2,cecropins2andcecropins3) and four transcription factors (TFs) (dif1,dif2,relishandjnk) were significantly decreased under LPS and PGN stimulation, leading to increased mortality ofT. castaneumwhen infected with Gram-positiveStaphylococcus aureusor Gram-negativeEscherichia coliinfection. CONCLUSION TcCTL3 could mediate the immune response inT. castaneumvia the pattern recognition, agglutination and AMP expression. These findings indicate a potential mechanism of TcCTL3 in resisting bacteria and provide an alternative molecular target for pest control.