Distinct functional roles of HaPCS1and HaPCS2 in Helianthus annuus: Complementary phytochelatin synthases for heavy...

This study elucidates the distinct roles of two phytochelatin synthase (PCS) isoforms, HaPCS1and HaPCS2, from the hyperaccumulator Helianthus annuus (sunflower) in heavy metal detoxification. Gene expression analysis revealed pronounced functional divergence: HaPCS1 exhibited broad responsiveness, with significant upregulation across leaves, stems, and roots under NaCl, H₂O₂, and heavy metal (Cd²⁺, Ni²⁺, Pb²⁺, As³⁺) stress, peaking at 24 h, indicating a systemic role in stress mitigation. Conversely, HaPCS2 displayed leaf-specific expression, with robust induction primarily by heavy metals, suggesting a specialized role in aerial tissue detoxification. Heterologous expression of GST-HaPCS1and GST-HaPCS2 in Escherichia coli confirmed their distinct enzymatic profiles: the isoform HaPCS1 catalyzed a diverse range of phytochelatins (PC₁-PC₄), while the isoform HaPCS2 predominantly produced PC₂, with optimal solubility achieved at 30 °C with 20 μM CdCl₂. Both isoforms enhanced bacterial tolerance to Ni²⁺ and As³⁺, but HaPCS2 demonstrated superior bioaccumulation, achieving 5211 μg/g DCW for Cd²⁺ and 458 μg/g DCW for As³⁺, compared to HaPCS1's 2793 μg/g DCW and 357 μg/g DCW, respectively. These results highlight the complementary yet distinct roles of HaPCS1and HaPCS2, emphasizing their specialized contributions to metal detoxification and their significant potential for bioremediation applications.