Populus euphratica plant cadmium resistance 2 mediates Cd tolerance by root efflux of Cd ions in poplar.

Abstract

Populus euphratica PePCR2 increases Cd resistance by functioning as a Cd extrusion pump and by mediating the expression of genes encoding other transporters. Cadmium (Cd) is a non-essential, toxic metal that negatively affects plant growth. Plant cadmium resistance (PCR) proteins play key roles in the response to heavy metal stress. In this study, we isolated the gene PePCR2 encoding a plant PCR from Populus euphratica. PePCR2 gene transcription was induced by Cd, and its transcript level peaked at 24h after exposure, at a level approximately 18-fold higher than that at 0h. The PePCR2 protein was localized to the plasma membrane. Compared with yeast cells harboring the empty vector, yeast cells expressing PePCR2 showed enhanced Cd tolerance and a lower Cd content. Compared with wild-type (WT) plants, poplar overexpressing PePCR2 showed higher Cd resistance. Net Cd2+ efflux measurements showed that Cd2+ efflux from the roots was 1.5 times higher in the PePCR2-overexpressing plants than in WT plants. Furthermore, compared with WT plants, the PePCR2-overexpressing plants showed increased transcript levels of ABCG29, HMA5, PDR2, YSL7, and ZIP1 and decreased transcript levels of NRAMP6, YSL3, and ZIP11 upon exposure to Cd. These data show that PePCR2 increased Cd resistance by acting as a Cd extrusion pump and/or by regulating other Cd2+ transporters to decrease Cd toxicity in the cytosol. The results of this study identify a novel plant gene with potential applications in Cd removal, and provide a theoretical basis for reducing Cd toxicity and protecting food safety.