Foliar Silicon Nanoparticles Induce Coordinated Defense against Cadmium in Rice via Jasmonate-Mediated Metabolic Reprogramming

Foliar application of silicon nanoparticles (SiNPs) is a promising strategy for mitigating cadmium (Cd) contamination in rice; however, the systemic mechanisms remain poorly understood. Here, we reveal that foliar SiNPs activate a coordinated defense orchestrated by jasmonate (JA) signaling. 100 mg/L SiNPs reduced grain Cd by 66.58% and increased yield by 38.14%. Driven by this systemic regulation, the defense manifests in two dimensions: (1) internally, SiNP-activated JA signaling promoted Cd sequestration in leaf hemicellulose 2 fraction by 8.94% and regulated key transporter genes (upregulation of OsHMA3; downregulation of OsNramp1, OsZIP1, and OsZIP7); and (2) externally, this shoot-to-root signaling induced rhizosphere metabolic reprogramming (accumulation of secondary metabolites, lipids, and fatty acids) and recruited functional microbes (Desulfovibrio, Gallionellaceae, and Bacillus), resulting in a 17.02% reduction in bioavailable Cd via enriched oxygen-containing functional groups in soil. This work elucidates a novel biogeochemical framework for developing nanotechnology-based strategies for safe rice production in Cd-contaminated fields.