Nanoplastics, but Not Microplastics, Enhance Plant Resistance to Herbivores Through Defence Priming

The accumulation of nano/microplastics (N/MPs) in wetlands has significant physiological effects on plants, which often simultaneously suffer herbivore attacks. However, how N/MPs interfere with interspecific interactions between wetland plants and herbivores remains poorly understood. Here, we pre-exposed Phragmites australis to N/MPs (100 nm/2 μm; 10, 50 and 100 mg/L) for 1 week, followed by co-exposure to N/MPs and Thrips sp., to determine the effect of N/MPs on the plant's insect resistance. NP exposure significantly increased P. australis biomass upon thrips attacks, while MPs exhibited no effects on reed growth. The exposure of 100 mg/L NPs alleviated root oxidative stress, feeding damage and photodamage caused by thrips and triggered stronger hormone signal transduction than MPs. In particular, 100 mg/L NPs upregulated transcription factors and DNA methylation to activate defence priming in roots, as well as histone modification in leaves. Metabolomics verified that P. australis accumulated more jasmonic acid, insect-resistant metabolites, indole-3-acetic acid, auxin and central metabolism-related metabolites, which help plants to defend against herbivores and facilitate growth. These results elucidate the molecular mechanism by which NPs mediated plant defence priming against herbivores, contributing to a better understanding of the ecological impacts of emerging contaminants and providing new insights into wetland conservation and ecological management.