Abstract:

【Aim】 To explore the molecular characteristics and biological function of the glutathione S-transferase (GST) gene LsGSTe1 from the cigarette beetle, Lasioderma serricorne. 【Methods】 Based on the transcriptome database of L. serricorne, the full-length cDNA of LsGSTe1 was cloned using RT-PCR and then subjected to bioinformatics analysis. The expression levels of LsGSTe1 in different developmental stages (early instar larva, late instar larva, pupa, callow adult, and mature adult) and different tissues (integument, midgut, fat body, and Malpighian tubules) of the late instar larvae of L. serricorne, and the changes in the expression level of LsGSTe1 in the 5th instar larvae after exposure to ethyl formate fumigation were detected via qPCR. The target gene LsGSTe1 in the 5th instar larvae of L. serricorne was further knocked down by RNAi, and the changes in the susceptibility of the larvae to ethyl formate fumigation were determined by insecticide bioassay. 【Results】 The full-length cDNA sequence of LsGSTe1 in L. serricorne was cloned and deposited at GenBank under the accession number MN480468. The open reading frame of LsGSTe1 is 684 bp in length encoding a 227-amino-acid protein. LsGSTe1 has the conserved catalytic sites at the N-terminal domain and C-terminal domain. Phylogenetic analysis revealed that LsGSTe1 belongs to the Epsilon family of GSTs. The qPCR results showed that LsGSTe1 was constitutively expressed in the tested developmental stages and had a relatively higher expression level in the late instar larva. Tissue-specific expression profiles showed that the expression level of LsGSTe1 was the highest in the fat body, followed by in the midgut and integument, and the lowest in Malpighian tubules. The expression level of LsGSTe1 in the 5th instar larvae subjected to fumigation treatment with LC₃₀ (10 μL/L) and LC₅₀ (20 μL/L) of ethyl formate was significantly increased by 2.96 and 5.80 times as high as that of the control, respectively. RNAi results showed that the expression levels of LsGSTe1 were significantly reduced by 79.9% and 83.0% at 48 and 72 h after RNAi, respectively. The mortality of the 5th instar larvae treated with the LC₅₀ of ethyl formate in the dsLsGSTe1 injection group at 72 h after RNAi increased by 32.4% as compared with that of the control group (dsGFP injection group). 【Conclusion】 It is inferred that LsGSTe1 may be involved in the detoxification of ethyl formate in L. serricorne. 

Key words: Lasioderma serricorne, glutathione S-transferase, gene expression, ethyl formate, RNA interference