The Sedum plumbizincicola defensin gene, SpPDF, conferred cadmium accumulation via its chelation

Heavy metal pollution, particularly cadmium (Cd), is a significant environmental and health concern due to its high mobility and bioaccumulation potential. Our study identifies a novel Cd-responsive chelation protein gene, SpPDF, from the hyperaccumulator plant Sedum plumbizincicola, which enhances Cd tolerance through chelation. The SpPDF, belonging to the Knot1 superfamily and lacking a signal peptide, is primarily expressed in roots and is significantly induced by Cd treatment. Subcellular localization studies revealed a cytoplasmic distribution of the SpPDF protein. Heterologous expression in yeast demonstrated that SpPDF improves Cd tolerance and in vitro Cd-binding experiments confirmed SpPDF's chelation activity. Overexpression of SpPDF in plants significantly increased Cd accumulation in roots and decreased it in shoots, attributed to enhanced root chelation capacity and reduced translocation to above-ground parts. This study provides a new molecular approach for improving plant remediation of Cd pollution, challenging the view that defensins are exclusively secreted proteins. Our findings offer valuable insights for the molecular breeding of plants for the phytoremediation of Cd-contaminated soil.