Physiological and molecular mechanisms of silicon and potassium on mitigating iron-toxicity stress in Panax ginseng

Iron plays a crucial role in plant chlorophyll synthesis, respiration, and plant growth. However, excessive iron content can contribute to ginseng poisoning. We previously discovered that the application of silicon (Si) and potassium (K) can mitigate the iron toxicity on ginseng. To elucidate the molecular mechanism of how Si and K alleviate iron toxicity stress in ginseng. We investigated the physiological and transcriptional effects of exogenous Si and K on Panax ginseng. The results suggested that the leaves of ginseng with Si and K addition under iron stress increased antioxidant enzyme activity or secondary metabolite content, such as phenylalanine amino-lyase, polyphenol oxidase, ascorbate peroxidase, total phenols and lignin, by 6.21%-25.94%, 30.12%-309.19%, 32.26%-38.82%, 7.81%-23.66%, and 4.68%-48.42%, respectively. Moreover, Si and K increased the expression of differentially expressed genes (DEGs) associated with resistance to both biotic and abiotic stress, including WRKY (WRKY1, WRKY5, and WRKY65), bHLH (bHLH35, bHLH66, bHLH128, and bHLH149), EREBP, ERF10 and ZIP. Additionally, the amount of DEGs of ginseng by Si and K addition was enriched in metabolic processes, single-organism process pathways, signal transduction, metabolism, synthesis and disease resistance. In conclusion, the utilization of Si and K can potentially reduce the accumulation of iron in ginseng, regulate the expression of iron tolerance genes, and enhance the antioxidant enzyme activity and secondary metabolite production in both leaves and roots, thus alleviating the iron toxicity stress in ginseng.