A Transcriptomic Study on the Toxic Effects of Iodide (I^-) Wet Deposition on Pepper (Capsicum annuum) Leaves

Radioactive iodine (¹²⁹I), released into the environment from human nuclear activities, poses significant health risks to the biosphere due to its long half-life and mobility. This study investigates the toxic effects of wet-deposited iodine on the growth of chili pepper seedlings (Capsicum annuum L.) under soil cultivation conditions. Using sodium iodide (NaI) as the exposure agent, transcriptomic analysis was conducted to evaluate the molecular responses of chili pepper leaves to iodine at concentrations of 2, 4, and 8 ppm. The study identified 2440 and 1543 differentially expressed genes (DEGs) in leaves exposed to 2 ppm vs. 4 ppm iodine and 2 ppm vs. 8 ppm iodine, respectively. GO enrichment analysis showed that DEGs at 4 ppm were significantly associated with protein-chromophore linkage, extracellular region, and iron ion binding, while those at 8 ppm were enriched in defense response, cell wall components, and iron ion binding. Iodine stress disrupted key pathways associated with photosynthesis, antioxidant defense, and cuticle biosynthesis. In particular, the downregulation of key genes related to protein-chromophore binding, lipid metabolism, and cell wall organization indicated reduced photosynthetic efficiency and weakened stress resistance. This study provides molecular-level insights into the ecological risks of iodine stress in plants and offers a scientific basis for managing iodine contamination and breeding iodine-tolerant chili pepper cultivars.