Defensin proteins AtPDF1.2A and AtPDF1.2C mediate cadmium accumulation and plant growth in Arabidopsis

Cadmium is transported in xylem sap as Cd²⁺ or Cd-protein chelates, which regulates shoot Cd accumulation; however, the proteins involved in this process have remained unknown in Arabidopsis. Here, we identified eight Cd-inducible defensin proteins in xylem sap and further investigated the functions of AtPDF1.2A and AtPDF1.2C. Tissue expression analysis revealed that the expression level of AtPDF1.2A was higher than that of AtPDF1.2C. Both proteins were localized to the cytoplasm and cell wall, and their expression was strongly induced by Cd. Heterologous expression of AtPDF1.2A enhanced Cd tolerance in yeast, whereas AtPDF1.2C did not; both significantly reduced Cd content in E. coli and yeast. In vitro Cd-binding assays confirmed that both AtPDF1.2A and AtPDF1.2C possess Cd-chelating activity. Hydroponic experiments revealed that AtPDF1.2A regulates plant growth and modulates sensitivity to Cd stress. Overexpression of AtPDF1.2A increased root Cd content, while atpdf1.2a mutant lines decreased shoot Cd content. AtPDF1.2C positively regulated growth, but it did not affect Cd tolerance. Its overexpression increased shoot Cd content. In summary, AtPDF1.2A and AtPDF1.2C chelate Cd and mediate its efflux into the xylem sap for transport, thereby regulating shoot Cd accumulation. These findings enrich our understanding of the molecular regulatory mechanisms of Cd accumulation in plants.