Expression profile of two HSP70 chaperone proteins in response to extreme thermal acclimation in Xestia c-nigrum (Lepidoptera: Noctuidae)

Heat shock proteins 70 (HSP70s) are highly evolutionarily conserved and play important roles in helping insects survive under extreme temperatures. In this study, Xestia c-nigrum (L.) (Lepidoptera: Noctuidae) was stressed at various temperatures, and the impacts on thermotolerance and cold endurance were examined. Two complementary deoxyribonucleic acid (cDNA) clones encoding heat shock cognate 70 (HSC70) and inducible heat shock protein 70 (HSP70), named Xc-HSC70 and Xc-HSP70, respectively, were isolated from X. c-nigrum using reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). Amino acid sequence analysis indicated that Xc-HSC70 and Xc-HSP70 contained the signature sequences of the HSP70 family, and phylogenetic analysis showed that Xc-HSP70s were consistent with the known insect classification. Genomic DNA structure analysis revealed that the Xc-HSC70 gene contained 8 introns that all conformed to the GT/AG rule, whereas the Xc-HSP70 gene did not contain any introns in the coding region. Fluorescent real-time quantitative RT-PCR revealed that both genes were significantly up-regulated under thermal stress and cold stress. The expression patterns indicated that Xc-HSP70 was heat inducible and Xc-HSC70 was constitutively expressed. The temperature response was more intense for Xc-HSP70 than for Xc-HSC70, regardless of the temperature or developmental stage; however, the expression of Xc-HSC70 and Xc-HSP70 was not altered in the pupa. Taken together, the expression profiles of both genes (Xc-HSP70s) provide good support to the insect for coping with adverse conditions.