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 (H 2 O 2 ), 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.
Rong et al. (Tue,) studied this question.