Metal-tolerance protein PCR2 enhances Cd tolerance by root efflux of Cd ions in poplar

Abstract Cadmium (Cd) is a non-essential, toxic metal that affects plant growth. Plant cadmium-resistance (PCR) proteins play key roles in responding to heavy metal stress. In this study, we isolated the PCR gene PePCR2 from Populus euphratica. PePCR2 gene transcription was induced by Cd and peaked at 24 h after exposure; the PePCR2 protein was localized to the plasma membrane. Expressing PePCR2 in yeast enhanced the tolerance of yeast cells to Cd and decreased Cd content. Overexpression of PePCR2 in poplar conferred higher Cd resistance than in wild-type plants. Net Cd2+ efflux measurements showed increasing Cd2+ efflux in transgenic roots compared with wild-type plants. Furthermore, the overexpression of PePCR2 in poplar increased the transcription levels of ABCG29, HMA5, PDR2, YSL7, and ZIP1 and decreased that of NRAMP6 upon exposure to Cd. These data showed that PePCR2 increased Cd resistance by acting as a Cd extrusion pump or by regulating other Cd2+ transporters to decrease Cd toxicity in the cytosol. Our study provides an effective genetic resource for reducing Cd accumulation in plants.