Multigene Coexpression (HMA9-CadWp-ZIP6) Enables Cadmium-Hyperaccumulating Transgenic Poplar for Efficient Soil Remediation

Poplar shows promise for cadmium (Cd(II)) phytoremediation due to its rapid growth and high biomass yet lacks hyperaccumulation capacity. Here, the <i>ZIP</i> and <i>HMA</i> gene families were identified in poplar. Under Cd(II) stress, <i>ZIP6</i> expression in poplar roots decreased, while <i>HMA9</i> expression increased over time. CadWp can chelate Cd(II) in vitro. Overexpression (OE) and reduced expression (RE) transgenic poplar lines of these genes were generated. OE/RE <i>ZIP6</i> lines demonstrated that this gene enhanced Cd(II) absorption in roots, while OE/RE <i>HMA9</i> lines demonstrated that this gene facilitated Cd(II) transport. OE <i>CadWp</i> in poplar largely alleviates the toxicity of Cd(II). Then, poplar lines (OE <i>9HCZ</i>) with simultaneous overexpression of <i>HMA9-CadWp-ZIP6</i> were generated and accumulated higher Cd(II) levels with a minimal growth penalty. In summary, we identified genes involved in Cd(II) absorbing, transporting, and detoxification, and coexpression of these genes in poplar enabled the development of new biomaterials for Cd(II)-contaminated soil phytoremediation.