Organic Cation Transporter Mediates the Uptake of Quaternary Ammonium Compounds in Arabidopsis

Quaternary ammonium compounds (QACs), widely used in consumer products and pharmaceuticals, are increasingly released into soils and can accumulate in plants, posing significant ecological and health risks. While plant uptake mechanisms for QACs remain poorly characterized, this study identifies organic cation transporter 1 (OCT1) as a potential mediator of QAC absorption in Arabidopsis. Root uptake experiments demonstrated reduced QAC accumulation under treatments with metabolic and OCT inhibitors. Transcriptional upregulation of AtOCT1 in QAC-exposed wild-type plants, along with functional validation through yeast heterologous expression systems, implicated this transporter in cationic pollutant absorption. Comparative analysis revealed 12%-42% lower root QAC concentrations in AtOCT1 mutants compared to wild-type plants, while overexpression lines exhibited 9.4%-43% increases in accumulation alongside enhanced sensitivity. Molecular docking simulations demonstrated stronger binding affinities between AtOCT1 and QACs compared to its native substrate L-carnitine, with microscale thermophoresis confirming direct interactions. Quantitative structure-activity relationship analysis identified electronic energy, molecular weight, and polarizability as critical determinants of AtOCT1-mediated transport efficiency. These findings establish the biological and structural role of AtOCT1 in cationic pollutant uptake, advancing mechanistic understanding of transporter-mediated plant accumulation of ionizable organic pollutants.