Regulation of cadmium tolerance and accumulation by miR156 in Arabidopsis.

Plants have evolved effective strategies to cope with heavy metals Cd toxicity, but the regulatory mechanism underlying Cd tolerance and accumulation are still poorly understood. miR156 has been shown to be the master regulator of development and stress response in plants. However, whether miR156 is also involved in plant Cd stress response remains unknown. Here, we show that plants overexpressing miR156 (miR156OE) accumulated significantly less Cd in the shoot, and conferred enhanced tolerance to Cd stress. Plants with a knocked-down level of miR156 (MIM156) were sensitive to Cd stress, and accumulated significantly higher Cd. Under Cd stress, miR156OE had significantly longer primary root length, higher biomass and chlorophyll content, increased activities of antioxidative enzymes and lower levels of endogenous reactive oxygen species (ROS), while MIM156 had the opposite phenotype. To investigate the underlying mechanism of miR156-mediated Cd stress response in Arabidopsis, we profiled the expression of several Cd transporter genes. The expression of Cd uptake transporter of AtZIP1、AtZIP2 and vacuole segregated transporter AtABCC1 was significantly elevated in miR156OE, whereas it was significantly reduced in MIM156. MIM156 also led to an elevated level of AtHMA4 responsible for transporting Cd from the root to the shoot. Our results indicate that miR156 acts as a positive regulator of plant tolerance to Cd stress by modulating ROS levels and Cd uptake/transport genes expression. Therefore, our study adds a new layer of regulatory mechanism for Cd transport and tolerance in plants, and provides a perspective to regulate Cd transport artificially by modulating plant vegetative growth and development using miR156.