Over-expression of the poplar expansin gene PtoEXPA12 in tobacco plants enhanced cadmium accumulation

As important cell wall proteins in plants, expansins are involved in a serious of abiotic stress resistance such as drought, heat, salt, even heavy metals. To understand the role of expansins in cadmium (Cd) stress, we analyzed the expression patterns of 36 expansin genes in Populus tomentosa. A Cd-induced expansin gene, PtoEXPA12, was identified, cloned, and transformed into tobacco plants. After treatment with Cd, the transgenic plants showed stronger symptoms of Cd toxicity as to the wild-type tobacco plants. Further physiological tests showed that the transformants had higher relative electrolyte leakage and superoxide dismutase activity, more malondialdehyde and H2O2 content, and lower chlorophyll content in Cd stress. Cd content measurement showed it is 1.40-2.07-fold higher and 1.29-1.38-fold higher separately in roots and shoots of transgenic plants than those in wild-type plants, while the transfer coefficient value kept invariably even decreased. Therefore, PtoEXPA12 was really involved in Cd uptake and accumulation, and led to Cd toxicity of cells. It would be a potentially applicable part in phytoremediation system.