Silicon accumulation in shoots suppresses cobalt uptake in rice through cobalt transporter gene downregulation

Cobalt (Co) enrichment in agricultural soils presents growing concerns for food security and human well-being. Although silicon (Si) is known to mitigate the toxicity of several heavy metals in plants, its specific role in regulating Co behavior in rice remains insufficiently characterized. Here, Si-Co interactions were examined with a silicon-deficient rice mutant (lsi1) alongside its wild-type (WT) control. Increasing Co levels inhibited primary root elongation in both genotypes, yet the presence of Si did not directly abolish this toxicity. Instead, Si addition significantly reduced Co concentrations in the shoots, roots, root cell sap, and xylem sap of WT plants, whereas the lsi1 mutant showed no comparable response. Si pretreatment likewise constrained Co accumulation only in the WT. A split-root system further demonstrated Si accumulation in shoots, instead of in roots alone, is essential for limiting Co uptake. At the transcriptional level, Si supplementation suppressed essential Co influx-mediating transporter OsNramp5 expression in WT roots but had no effect in the lsi1 mutant. Collectively, Si accumulation in shoots appears to reduce Co uptake through the downregulation of the expression of a key Co transporter gene in rice.