Salvia miltiorrhiza-derived carbon dots alleviate cadmium stress in flowering Chinese cabbage by suppressing BrTCP9-mediated cadmium transport and reactive oxygen species metabolism

Abstract

Cadmium stress not only inhibits vegetable growth but also threatens food safety. Carbon dots (CDs) and TCP transcription factors play crucial roles in responding to abiotic stress. As a leafy vegetable, flowering Chinese cabbage exhibits heightened vulnerability to cadmium contamination. However, the molecular mechanism by which CDs may alleviate cadmium stress through TCP-mediated regulation of cadmium transport and reactive oxygen species (ROS) metabolism remains unclear. In this study, we found that Salvia miltiorrhiza-derived CDs (SmCDs) alleviated cadmium stress in flowering Chinese cabbage in a concentration-dependent manner. An optimal concentration of SmCDs significantly enhanced cadmium tolerance and plant growth. Furthermore, TCP transcription factor simultaneously induced by cadmium and suppressed by SmCDs was identified as BrTCP9, while the cadmium transporter and Rboh gene were identified as BrNramp1.2 and BrRbohA, respectively. Under cadmium stress, silencing BrTCP9, BrNramp1.2, or BrRbohA markedly suppressed ROS production, reduced both cadmium and malondialdehyde accumulation, and promoted plant growth, with SmCDs application further enhancing these effects. Intriguingly, BrNramp1.2 and BrRbohA were found to mutually regulate each other under cadmium stress. Y1H, LUC, GUS, and EMSA assays confirmed that BrTCP9 directly binds to the promoter of BrNramp1.2 and BrRbohA, activating their expression. These results indicated that BrTCP9, BrNramp1.2, and BrRbohA negatively regulated cadmium tolerance, whereas SmCDs mitigated cadmium stress by suppressing BrTCP9-mediated BrNramp1.2 and BrRbohA expressions. This study not only expanded the molecular network of cadmium stress response but also provided theoretical foundation for the application of carbon nanomaterials in agricultural heavy metal remediation.