Sulfotransferases in Cardamine hupingshanensis: Identification, expression, and regulatory role in selenium...

Sulfotransferases (SOTs), essential enzymes in selenium metabolism, catalyze the transfer of selenate from donor molecules to hydroxyl groups of acceptor molecules such as jasmonic acid (JA). In this study, the analysis identified 32 ChSOT genes tandemly duplicated across C. hupingshanensis's 12 chromosomes, with their proteins primarily localized in the cytoplasm and cell membrane. Analysis of ChSOT gene structure and function showed conserved motifs and domains, with 35 regulatory elements in their promoters mainly linked to plant hormone responses including JA regulation, light reactions, and abiotic stress. Gene expression analysis shows that ChSOT15-1 is a major gene of the ChSOT family that responds to selenium stress, and the relative expression level was upregulated 529 and 219-fold in leaves with 100 μg Se L^-1 and 80,000 μg Se L^-1 selenite, and upregulated 12 and 152-fold in roots, respectively. Molecular docking analysis revealed two key findings: The identified substrates included 3'-phosphoadenosine-5'-phosphoselenate (PAPSe) and hydroxyl-containing small molecules (e.g., JA pathway metabolites, JA derivatives, and flavonoids). ChSOT15-1 exhibited the highest binding affinity in pocket 3, where conserved structural motifs interacted with catalytic residues Thr¹³⁷, Asn¹³⁹, and His¹⁴¹ during PAPSe binding. This study provides the first evidence that sulfotransferases participate in selenium metabolism, demonstrating how ChSOT15-1 mediates selenation of hydroxylated small molecules (e.g., JA) under selenium stress, potentially contributing to both selenium detoxification and JA homeostasis regulation.