miR408-5p and miR408-3p cooperatively reduce cadmium uptake and accumulation in rice

In plants, a subset of miRNA precursors can yield multiple mature miRNAs; however, how they simultaneously regulate a single biological process remains poorly understood. Cadmium (Cd) is a non-essential heavy metal toxic to plants, posing serious risks to human health via the food chain. As rice is a major dietary source of Cd, elucidating the molecular mechanisms underlying Cd accumulation is crucial for ensuring food safety. Here, we show that a pair of miRNAs derived from the MIR408 precursor cooperatively represses Cd uptake in roots by targeting distinct genes, consequently reducing Cd accumulation in rice grains. miR408-5p inhibits translation of Heavy metal-associated Isoprenylated Plant Protein 9 (HIPP19), which is specifically expressed in exodermis and endodermis cells and facilitates Cd binding. Meanwhile, miR408-3p cleaves Uclacyanin 7 (UCL7) mRNA, leading to enhance the activity of superoxide dismutases (SODs), and increase production of reactive oxygen species (ROS), particularly hydrogen peroxide (H2O2), which in turn suppresses Cd absorption and accumulation. Furthermore, knockout mutants of HIPP19 and UCL7, as well as MIR408 overexpressing lines, exhibit significantly decreased Cd content in grains, while the accumulation of other essential metals remains comparable to that of wild-type plants. These findings establish a promising strategy for producing "low-Cd rice" without compromising agronomic traits for food safety.