The effect of Polyethylene Terephthalate (PET) Microplastic stress on the composition and gene regulatory network of amino acid in Capsicum annuum

Polyethylene Terephthalate (PET) is a widely used plastic in daily life. The extensive accumulation of PET microplastics (PET-MPs) in the environment adversely affects plant growth in multiple ways. However, the impact of PET-MPs exposure on the plant metabolism and the underlying molecular mechanisms are largely unexplored. To address this gap, we employed metabolomics and transcriptomics combination analyses to investigate the effects of PET-MPs exposure, varying in particle size and concentration, on the amino acid content and composition in pepper, as well as the underlying genes regulatory network. A total of 282 amino acids and their derivatives were identified, including 8 essential amino acids. Significant changes in differentially accumulated amino acids (DAAs) and differentially expressed genes (DEGs) were observed across different treatments, indicating that PET-MPs exposure affects amino acid metabolism in peppers, with these effects closely related to the size and concentration of PET-MPs. Ten DAAs with significant variable importance were identified through OPLS-DA. Weighted gene co-expression network analysis (WGCNA) revealed that the red module was significantly correlated with most of the DAAs indicators, highlighting the essential roles of HMSI, BCAT, and 12 transcription factor (TF) genes in regulating amino acid synthesis under PET-MPs exposure. Furthermore, correlation and redundancy analysis (RDA) identified three candidate genes, HSMI, PROC, and FHM, involved in amino acid biosynthesis pathways. This study enhances our understanding of MPs pollution and provides novel insights into the impact of MPs on crop growth and nutrition.