Effect of Exogenous STTM397 and miRNA397 on Cadmium Uptake and Accumulation in Water Spinach ( Ipomoea aquatica )

Cadmium (Cd) contamination in edible crops poses severe risks to human health and necessitates innovative, nontransgenic mitigation strategies. Here, we report a hydroponic delivery system for synthetic double-stranded RNAs (dsRNAs) targeting miRNA397 in water spinach (Ipomoea aquatica). Cy3-labeled miRNA397 and its short tandem target mimic (STTM397) were efficiently taken up by root epidermal cells and translocated via xylem to shoots. Exogenous miRNA397 suppressed LAC3 and LAC12 expression, reduced laccase activity and lignin deposition, and facilitated Cd translocation into stele and aerial tissues, resulting in increased shoot Cd accumulation and reactive oxygen species (ROS) generation. In contrast, STTM397 counteracted miRNA397, restored LAC3 and LAC12 expression and lignin biosynthesis─particularly in the epidermis and Casparian strip─enhanced Cd sequestration in the root and alleviated Cd-induced ROS. This dsRNA-mediated strategy precisely modulates Cd uptake via the miRNA397-laccase-lignin pathway, offering a transgene-free platform to reduce dietary Cd exposure.