DcHsp17.7, a small heat shock protein from carrot, is upregulated under cold stress and enhances cold tolerance by functioning as a molecular chaperone

Abstract

The expression profile and functional properties of DcHsp17.7, a small heat shock protein from carrot (Daucus carota L.), were examined under cold stress. Immunoblot analysis showed that low temperature (2 °C) induced DcHsp17.7 in vegetative tissues. Differential accumulation of the transcript and protein under the cold suggests that expression of DcHsp17.7 might be controlled at the transcriptional and/or translational levels. To examine the functional properties of DcHsp17.7, the gene was expressed in Escherichia coli. When exposed to 2 °C for 10 days, transformed cells expressing DcHsp17.7 showed 115% cell viability, whereas control cells recorded 24%, suggesting that DcHsp17.7 can confer cold tolerance. The amount of soluble protein under the cold was 83% in transformed cells expressing DcHsp17.7, whereas the control cells showed only 52%, suggesting that DcHsp17.7 functions as a molecular chaperone preventing cold-induced protein degradation. Native-polyacrylamide analysis revealed that DcHsp17.7 was found in two oligomeric complexes ('160 and 240 kDa) and possibly multiple complexes (from 300 to 450 kDa) in cold-stressed carrot and transformed E. coli, respectively. During prolonged cold stress, these complexes disappeared and then reappeared, suggesting that the dissociation and reassociation of DcHsp17.7 complexes might be important for the function of the protein.