A heat shock cognate 70 gene in the endoparasitoid, Pteromalus puparum, and its expression in relation to thermal stress

The Pphsc70 (heat shock cognate 70) gene was isolated from the endoparasitoid Pleromalus puparum and then characterized. The full-length cDNA was 2204 base pair (bp) and contained a single 1968 bp ORF that encoded a polypeptide of 656 amino acids with a predicted molecular mass of 71.28 kDa. Phylogenetic analysis based on Hsc70 amino acid sequences from fifteen insect species agreed with the present phylogeny. In addition, genomic DNA confirmed the presence of three introns located at the coding region as well as the 5'UTR. A significant elevation of Pphsc70 expression was observed following heat treatment, however, continued exposure to heat shock or recovery caused the expression of induced mRNA to gradually decline to levels that were significantly lower than those of control pupae (P < 0.05). In addition, a significant increase was observed in the emergence rate of pupae that were preheated at 40 degrees C and then exposed to 50 degrees C for I h when compared with the pupae that were not preheated, but instead directly exposed to 50 degrees C. Taken together, these results revealed that exposure to gradually increasing temperatures can enhance an insects thermo-tolerance.