Microplastic-Derived Dissolved Organic Matter Inhibits Plant Root Growth by Disrupting Polar Auxin Transport via Specific Molecular Fractions

The adverse effects of microplastic particles on plant growth have been extensively studied, but the ecological risks caused by microplastic-derived dissolved organic matter (MP-DOM), which is substance continuously released from microplastics and highly bioavailable, still remain largely unexplored, especially its toxic effects and underlying mechanisms on plant growth. Here, we employed multiomics combined with transgenic materials to investigate the effects of different MP-DOM types, including PP-DOM, PS-DOM, and PBAT-DOM, on Arabidopsis root growth. The results indicated that PS-DOM and PBAT-DOM, but not PP-DOM, significantly inhibit root elongation in a dose-dependent manner by impairing the meristem zone and stem cell activity. Integrated transcriptomic and metabolomic analyses revealed that MP-DOM altered gene expression related to phenylpropanoid biosynthesis and the plant hormone signal transduction pathway. Molecular transformation network analysis revealed that low-polarity saturated molecules enriched in PS-DOM and PBAT-DOM perturbed the phenylpropanoid biosynthesis, thereby indirectly impairing auxin homeostasis. Phenotypic analysis of auxin reporter lines confirmed that PS-DOM and PBAT-DOM disrupt polar auxin transport by downregulating the expression of auxin transporters, leading to abnormal auxin accumulation and inhibition of root growth. This study elucidates the molecular mechanism underlying MP-DOM-induced phytotoxicity, providing insight into the ecological risk assessment of microplastics in agricultural production.