Genome-Wide and Transcriptomic Analyses Reveal That HcERF37 Activates HcPDR1 to Confer Cadmium Tolerance in Kenaf

Cadmium (Cd) stress severely compromises crop growth and yields globally. The APETALA2/Ethylene-Responsive Factor (AP2/ERF) family is essential in modulating plant tolerance to Cd. However, the molecular mechanisms governing AP2/ERF-driven adaptation to Cd stress in kenaf have remained largely unexplored. This study identified 213 HcAP2/ERF members within the kenaf genome and classified them into 11 distinct groups. Notably, nuclear-localized HcERF37 was significantly induced upon CdCl₂ exposure. Overexpression of HcERF37 in Arabidopsis markedly enhanced Cd tolerance, as evidenced by improved seed germination, seedling growth, and antioxidant capacity, alongside reduced Cd accumulation. Conversely, silencing HcERF37 in kenaf exacerbated Cd toxicity, resulting in substantial transcriptional reprogramming of stress-responsive genes. Mechanistic studies revealed that HcERF37 binds to the promoter of HcPDR1, facilitating Cd²⁺ extrusion from cells and thereby improving Cd tolerance. These findings reveal a novel regulatory axis, HcERF37-HcPDR1, providing valuable genetic resources for the development of Cd stress-resilient crops.