Abstract: 【Aim】 This study aims to clarify the function of an attacin gene (LsAttacin2) in Lasioderma serricorne larvae in response to bacterial infection.【Methods】The full-length cDNA sequence of LsAttacin2 from L. serricorne was amplified by RT-PCR. The relative expression levels of LsAttacin2 in different developmental stages (egg, early larva, late larva, pupa, callow adult and mature adult) and various tissues (head, cuticle, foregut, midgut, hindgut, fat body and Malpighian tubules) of the 4th instar larvae of L. serricorne, and in the 4th instar larvae after infection with Escherichia coli and Staphylococcus aureus and treatments with their peptidoglycans were examined by RT-qPCR. After silencing the expression of LsAttacin2 by RNAi through injection, the mortalities of the 4th instar larvae of L. serricorne post infection with E. coli and S. aureus were detected.【Results】The full-length cDNA sequence of LsAttacin2 (GenBank accession number: MT635176) in L. serricorne was obtained. The open reading frame of LsAttacin2 is 504 bp in length encoding 167 amino acid residues. LsAttacin2 has a signal peptide at the N-terminus and a conserved domain of Attacin_C superfamily at the C-terminus. The RT-qPCR results showed that LsAttacin2 was expressed in the tested various developmental stages and highly expressed in the late larva and pupa. LsAttacin2 was mainly expressed in immune tissues, such as midgut, cuticle and fat body of the 4th instar larva. Both E. coli and S. aureus and their peptidoglycan induced the up-regulated expression of LsAttacin2 in the 4th instar larvae of L. serricorne. RNAi combined with bacterial bioassay results showed that the expression levels of LsAttacin2 in the 4th instar larvae in the dsLsAttacin2 injection groups were significantly reduced by 72.8% and 80.4% at 24 and 48 h, respectively, as compared to those in the control groups (injected with dsGFP). The mortalities of the 4th instar larvae at 24 h after infection with E. coli and S. aureus in the dsLsAttacin2 injection groups at 48 h after RNAi increased by 21.1% and 24.4%, respectively, as compared to those in the control groups injected with dsGFP.【Conclusion】The results of this study suggest that LsAttacin2 plays an important role in the immune response of L. serricorne against the bacterial infections.

Key words: Lasioderma serricorne, attacin, gene expression, bacterial infection, immune; RNA interference