A Cytosolic Heat Shock Protein Expressed in Carrot (Daucus carota L.) Enhances Cell Viability under Oxidative and Osmotic Stress Conditions

The expression and function of DcHsp17.7, a small heat shock protein expressed in carrot (Daucus carota L), was examined under oxidative and osmotic stress conditions. Comparative analysis revealed that DcHsp17.7 is a cytosolic Class 1 protein. Sequence alignment showed that DcHsp17.7 has the characteristic a-crystalline domain-containing consensus regions 1 and II. Under oxidative [hydrogen peroxide (11202)1 and osmotic (polyethylene glycol) stress conditions, DcHsp17.7 accumulated in carrot leaf tissue. To examine its function under these abiotic stress conditions, the coding sequence of DcHsp17.7 was introduced into Escherichia coli and expressed by isopropyl beta-D-1-thiogalactopyranoside treatment. Under both oxidative and osmotic stress conditions, heterologously expressed DcHsp17.7 enhanced bacterial cell viability. The expression level of soluble proteins was higher in transgenic cells expressing DcHsp17.7 when compared with controls under these stress conditions. These results suggest that DcHsp17.7 confers tolerance to both oxidative and osmotic stresses and thereby functions as a molecular chaperone during the stresses examined.