Polyethylene Terephthalate Microplastics Induce More Pronounced Physiological and Molecular Responses in Pepper Plants than Polyethylene: Insights from Physiological, Transcriptomic, and Metabolomic Perspectives

Microplastics (MPs) threaten agroecosystems; however, polymer-specific phytotoxicity remains unclear. In this study, we integrated physiological, transcriptomic, and metabolomic analyses to examine the effects of polyethylene (PE) and polyethylene terephthalate (PET) on pepper (Capsicum annuum L.). MPs of both polymers inhibited growth in a dose-dependent manner, with PET inducing more severe root damage. PET upregulated photosynthesis-related genes in roots, suggesting systemic stress signaling or a compensatory response. Integrated transcriptomic and metabolomic analyses revealed that MPs inhibited the phenylpropanoid biosynthesis pathway in peppers by downregulating the expression of key enzymes, including PAL, C4H, and CCoAOMT, and reducing the production of downstream metabolites, such as chlorogenic acid, thereby disrupting plant defense mechanisms and secondary metabolic processes. Our results provide insights into the divergent phytotoxic effects of PE and PET and identify PET as a more potent stressor to crops, contributing to the risk assessment of MP pollution in agroecosystems.