Foxtail millet (Setaria italica L.) enhances leaf potassium content and promotes trehalose accumulation through the auxin signaling pathway to cope with PET nanoplastic stress

Foxtail millet, a C4 crop, exhibits high tolerance to abiotic stress. Our preliminary studies demonstrated that foxtail millet alleviates polyethylene terephthalate (PET) nanoplastic-induced oxidative stress by increasing leaf potassium (K⁺) content and promoting trehalose accumulation. In this study, exogenous application assays confirmed that elevated K⁺ levels drive trehalose biosynthesis, rather than the converse. Phytohormone analysis revealed significant changes in hormone levels, including auxin (IAA), abscisic acid (ABA), and 12-oxo-phytodienoic acid (12-OPDA), after exposure to PET nanoplastics, indicating their important roles in regulating plant responses to nanoplastic treatment. Mechanistic validation showed that auxin mitigates PET-triggered oxidative damage through dual pathways: transcriptional activation of potassium channel proteins and enhancement of trehalose-metabolizing enzyme activities, collectively elevating intracellular trehalose concentrations. Consistent with these findings, pretreatment with PET nanoplastics conferred cross-tolerance to salt stress in foxtail millet seedlings. Together, these results establish a novel molecular framework linking nanoplastic sensing to adaptive nutrient signaling, highlighting key regulatory nodes for engineering stress-resilient crops amid escalating environmental contamination. This study provides critical insights into sustainable agricultural strategies confronting combined plastic pollution and climate extremes.