Root-applied taurine reduces grain cadmium and improves rice yield by decreasing Cd transport and increasing Cd...

Taurine (TAU) can improve plant stress tolerance, but its effect on cadmium (Cd) accumulation in rice remains poorly understood. Here, we compared seed soaking, root application, and foliar spraying of TAU using hydroponic and full-season pot experiments with rice (Oryza sativa L. cv. Kitaake). The results showed that root application of TAU was the optimal approach, which can significantly promote rice growth and reduce Cd accumulation. In the hydroponic experiment, 10 mg L^-1 TAU increased shoot and root dry weights by 37.3% and 63.3%, respectively, and decreased shoot Cd concentration by 29.0%. In the pot experiment, root-applied TAU decreased brown-rice Cd concentration by 23.3% and increased grain yield by 14.7%. Root application of TAU reduced expression of OsNRAMP1, OsNRAMP5, OsIRT1, and OsIRT2 genes associated with Cd uptake and the OsHMA2 gene in charge of xylem loading by 29.7%, 11.4%, 48.8%, 11.1%, and 22.0%, respectively, whereas increased expression of the OsHMA3 gene involved in Cd vacuolar sequestration by 27.5%. Integrated transcriptomic, metabolomic, and physiological analyses showed that TAU activated the jasmonic acid signaling and phenylpropanoid pathway and promoted root cell-wall lignification, thereby increasing Cd retention in the cell wall by 20.2%. These results suggest that root-applied TAU decreases Cd accumulation in rice grain through coordinated changes in Cd uptake, translocation, and root retention while increasing grain production, offering a potential strategy for the safe utilization of Cd-contaminated paddy fields.