Identification of six heat shock protein 70 genes in Lasioderma serricorne (Coleoptera: Anobiidae) and their responses to temperature stress

Heat shock proteins (HSPs) play essential roles in stress tolerance in insects, such as the cigarette beetle, Lasioderma serricorne, which is an important pest of stored products. However, the function of HSPs in environmental stress response in L. serricorne is poorly understood. In this study, six cDNAs encoding putative HSP70s were identified in L. serricorne (LsHSP70-1 to LsHSP70-6). The LsHSP70 proteins identified have signature motifs of insect HSP70s and exhibit high amino-acid identity with their respective orthologs from other insect species. Phylogenetic analysis showed that these LsHSP70s fall into three major clans: HSP70 in the cytosol (four genes), endoplasmic reticulum (one gene), and mitochondria (one gene). LsHSP70 genes are differentially expressed in different developmental stages. LsHSP70-4 and LsHSP70-5 are mainly expressed at the larval stage, while LsHSP70-3 shows the highest level at the pupal stage. The other genes are ubiquitously expressed. Furthermore, the expression levels of LsHSP70-1 and LsHSP70-4 are significantly upregulated upon exposure to temperatures of both 0 and 15 degrees C, while LsHSP70-3 is inducible at 15 degrees C and LsHSP70-6 at 0 degrees C. In addition, treatment at 0 degrees C causes significant downregulation of LsHSP70-2 and LsHSP70-3. Exposure to a temperature of 30 degrees C upregulates LsHSP70-1 expression, while 35 and 40 degrees C treatments result in significantly enhanced transcription of all the LsHSP70 genes. To the best of the authors' knowledge, this is the first report on the sequence characteristics, phylogenetic relationships, and expression profiles of HSP70 genes in L. serricorne. The cold- and heat-inducible regulation of LsHSP70s suggests that these genes are related to tolerance of abnormal temperatures.