PmHMA3 enhances cadmium tolerance via transport and sequestration in Phytolacca americana

Soil cadmium (Cd) pollution poses a serious threat to agricultural product safety and ecosystem health. Using heavy metal hyperaccumulator plants for remediation is a promising strategy to alleviate Cd toxicity. The Heavy Metal ATPase (HMA) gene family plays a key role in plant heavy metal transport and tolerance. However, systematic studies of this gene family in the cadmium hyperaccumulator Phytolacca americana are still limited. In this study, we performed the first genome-wide identification of the HMA family in P. americana, uncovering 37 PmHMA genes. Our systematic analysis revealed their phylogenetic relationships, conserved motifs, and promoter architecture. Notably, promoter analysis showed an enrichment of stress-responsive elements (e.g., STRE, ARE), indicating a potential broad role in heavy metal stress responses. Further investigations demonstrated that PmHMA3 is localized to both the plasma membrane and the endoplasmic reticulum (ER). Its expression in roots was strongly induced by Cd stress, peaking at 24 h. Heterologous expression in yeast confirmed that PmHMA3 promotes cadmium uptake. Overexpression of PmHMA3 in Arabidopsis thaliana or complementation of the hma4 mutant significantly enhanced Cd tolerance. Preliminary mechanistic studies suggested that PmHMA3 may reduce cytoplasmic Cd concentration by sequestering Cd into the endoplasmic reticulum. These findings demonstrate that PmHMA3 mediates cadmium transport and compartmentalization through dual subcellular localization, thereby enhancing plant Cd tolerance and accumulation capacity. This study provides a key genetic resource for cultivating Cd-tolerant plants using PmHMA3, and lays the foundation for its application in phytoremediation, offering new strategies for the green management of Cd-contaminated soils.