SpHMA3: A Genetic Boost for Cadmium Tolerance and Bioremediation in Arabidopsis thaliana and Zea mays

In China, soil contamination by heavy metals is a widespread issue, with substantial increases in lead(Pb), cadmium(Cd), copper(Cu), and zinc(Zn) levels observed across various regions. Particularly, the concentrations of Pb and Cd significantly exceed their natural background levels. P-ATPases, a group of proteins, utilize energy from ATP hydrolysis to support the transmembrane movement of metal ions. This group encompasses several Heavy Metal Associated Transporter (HMA) ATPases. Studies on hyperaccumulators have shown the critical role of HMAs in the movement and reduction in Zn and Cd toxicity in plant systems. This research identifies a protein encoded by the <i>SpHMA</i> gene from Sedum <i>plumbizincicola</i>, a species noted for aiding Zn/Cd hyperaccumulators, which enhances tolerance to Cd and Zn. We detail a protein encoded by SpH/A within the HMA family that enhances Cd tolerance. Real-time fluorescence quantification (RT-PCR) indicates that <i>SpHMA3</i> expression in <i>Arabidopsis thaliana</i> and Zea mays <i>KN5585</i> correlates with high Cd tolerance, linked to Cd accumulation in Zea mays. In addition, homozygous <i>Arabidopsis thaliana AtHMA3</i> mutants exhibited increased Cd sensitivity compared to the wild type (<i>WT</i>). Notably, plants of <i>Arabidopsis thaliana</i> and <i>maize</i> overexpressing <i>SpHMA3</i> showed enhanced Cd stress tolerance compared to <i>WT</i>. Enhanced Cd accumulation in tissues was observed when <i>SpHMA3</i> was overexpressed, as revealed by subcellular distribution analysis. We propose that <i>SpHMA3</i> augments <i>maize</i> tolerance to Cd and Zn stresses through enhanced cellular uptake and translocation of Cd ions. This investigation clarifies the gene function of <i>SpHMA3</i> in Cd and Zn stress response, offering insights for enhancing heavy metal absorption traits in <i>maize</i> varieties and phytoremediation methods for soils contaminated with heavy metals.