Involvement of NF-κB transcription factors in antimicrobial peptide gene induction in the red flour beetle, Tribolium castaneum

► IMD-dependent antimicrobial peptide genes were revealed to be Rel-dependent. ► Toll-dependent antimicrobial peptide genes were shown to be Dif-dependent. ► Rel knockdown impaired host defense against two model bacterial pathogens. We previously demonstrated that Tribolium castaneum antimicrobical peptide (AMP) genes can be classified to IMD-dependent group I, Toll-dependent group III and co-dependent group II genes besides non-inducible group IV. Here, we focused on NF-κB transcription factor genes, Dif1, Dif2 and Rel, and examined their functions in AMP gene induction as well as linkages to the Toll or IMD pathway. IMD-dependent group I and Toll-dependent group III genes were revealed to be Rel- and Dif-dependent respectively through knockdown experiments, indicating that the pathway specificity of NF-κB classes found in Drosophila is also conserved in T. castaneum. The Toll–Dif and IMD–Rel pathways of T. castaneum were activated concomitantly by single microbe species, which may represent a distinctive feature of its immune responses. In addition, Rel knockdown impaired host defense against two model bacterial pathogens. Finally, potential κB motifs were searched in the regulatory regions of AMP genes, and relevance to respective NF-κB transcription factors was discussed.