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 ZIP and HMA gene families were identified in poplar. Under Cd(II) stress, ZIP6 expression in poplar roots decreased, while HMA9 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 ZIP6 lines demonstrated that this gene enhanced Cd(II) absorption in roots, while OE/RE HMA9 lines demonstrated that this gene facilitated Cd(II) transport. OE CadWp in poplar largely alleviates the toxicity of Cd(II). Then, poplar lines (OE 9HCZ) with simultaneous overexpression of HMA9-CadWp-ZIP6 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.