Heterologous Expression of a Carrot Small Heat Shock Protein Increased Escherichia coli Viability under Lead and Arsenic Stresses

The expression and function of DcHsp17.7, a small heat shock protein (sHSP), in carrot (Daucus carota L.) was examined under lead [Pb(II)] and arsenic (arsenate) stresses. In a time course experiment, the level of DcHsp17.7 increased in carrot leaf tissue treated with lead ions or arsenate. To examine the function of DcHsp17.7, the DcHsp17.7 gene was cloned and introduced into Escherichia coli. Heterologous expression of DcHsp17.7 was confirmed by immunoblot analysis using a polyclonal antibody raised against DcHsp17.7. Lead ion and arsenate reduced bacterial cell viability. However, transgenic E. coli with accumulated DcHsp17.7 showed higher levels of survival under both lead ion and arsenate conditions compared with the vector control. Immunoblot analysis showed that the level of heterologously expressed DcHsp17.7 decreased under lead ion conditions, but remained the same under arsenate conditions. Our results suggest that DcHsp17.7 can confer tolerances to lead and arsenic stresses.