The cigarette beetle, Lasioderma serricorne (Fabricius) (Coleoptera: Anobiidae), is a destructive stored pest distributed worldwide. Females typically oviposit in the stored materials, and the developing larvae tunnel through the stored food products on which they feed, resulting in tremendous damages to stored grains and seeds, tobacco, pet food, and dried flowers. Currently, excessive use of fumigation with insecticides has developed resistance to commonly insecticides in this insect, leading to environmental risk and its resurgence.
Controlled atmosphere (CA) treatments using low oxygen (O₂) and high carbon dioxide (CO₂) have been used commercially to control stored pests. The application of CA is a safe alternative way to chemical pesticides, and has been used to control the cigarette beetles. Our earlier studies showed that L. serricorne displayed a great capacity to withstand CO₂ stress. The activities of glutathione S-transferases (GSTs) in L. serricorne were significantly increased after exposed to CO₂ enriched atmosphere, implying that GSTs might be critical for tolerating to CO₂ stress. However, little is known about the molecular mechanism of GSTs in response to CO₂ exposure in L. serricorne.
In this study, three full-length cDNAs of GSTs in L. serricorne were cloned by reverse transcription-polymerase chain reaction (RT- PCR). The deduced amino acid sequence analysis of the three genes was performed by bioinformatics methods. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to establish expression profiles for those genes from different developmental stages and in response to CO₂ exposure. According to the predicted GST sequences from the transcriptome datesets of L. serricorne, the full-length cDNAs of three novel genes were obtained and named LsGSTt1, LsGSTd1 and LsGSTs1 (GenBank accession numbers: KY549655, KY549656, KY549657), respectively. The LsGSTt1 cDNA contained an open reading frame (ORF) of 564 nucleotides, encoding a polypeptide of 187 amino acids with an estimated molecular mass of 22.4 kDa and an isoelectric point (pI) of 8.54. The LsGSTd1 cDNA contained an ORF of 651 nucleotides, encoding a polypeptide of 216 amino acids with an estimated molecular mass of 24.5 kDa and a pI of 5.95. The LsGSTs1 cDNA contained an ORF of 696 nucleotides, encoding a polypeptide of 231 amino acids with an estimated molecular mass of 26.2 kDa and a pI of 5.06. Homology analysis indicated that the predicted amino acid sequences of the three genes had typical features of GSTs, including an N-terminal domain and a C-terminal domain. Phylogenetic analysis revealed that the three genes belonged to three different cytosolic classes, including Theta (LsGSTt1), Delta (LsGSTd1) and Sigma (LsGSTs1). Temporal expression profile revealed that all the three GSTs genes were constitutively expressed in the testing stages, exhibited similar developmental expression patterns, with the highest expression level measured in the early larval stage. Compared with the control, the mRNA levels of LsGSTd1 did not change significantly following exposure to CO₂ stress. However, when exposed to 50% lethal concentration (LC50) of CO₂, the expression levels of LsGSTt1 and LsGSTs1 were significantly increased.
In conclusion, the results suggest that LsGSTt1 and LsGSTs1 in L. serricorne might play important roles in defense responses challenged by CO₂ stress. This study provides the basis for clarifying the response mechanism of insects to CO₂ stress.