Integrative Network Analysis of Physiological, Transcriptomic, and Metabolomic Profiles Reveals the Mechanism of Propionic Acid-Mediated Alleviation of Cadmium Toxicity in Wheat ( <i>Triticum aestivum</i> L.)

Cadmium (Cd), a pervasive toxic metal, poses significant detrimental effects on plant development and yield. Exogenous propionic acid (PA) application significantly alleviated Cd toxicity in wheat seedlings. Based on physiological analysis, exogenous 10 μM PA treatment significantly reduced Cd accumulation by 36.29% in the shoot and 25.79% in the root under 20 μM Cd treatment. Integrative transcriptomic and metabolomic analyses revealed that PA enhances the antioxidant capacity via activation of branched-chain amino acid (BCAA) metabolism and salicylic acid (SA) signaling. Furthermore, PA upregulates <i>TaHSP20</i> expression through H₂O₂ signaling, promoting pectin synthesis and demethylation to improve Cd chelation in the cell wall. Additionally, PA activates abscisic acid (ABA) signaling, inducing the expression of <i>TaHSP20</i> and <i>TaHSP70</i> to reinforce cell wall biosynthesis and Cd sequestration. Key metabolites such as sedoheptulose and rhamnose may further facilitate Cd²⁺ immobilization within the cell wall. These findings elucidate a systemic mechanism underlying PA-mediated alleviation of Cd toxicity, offering new strategies for improving agroecological sustainability.