Integrative Physiology and Transcriptomics Reveal the Adaptive Mechanisms of Foxtail Millet (Setaria italica) in Response to LiCl Stress

Abstract

With the ubiquity of lithium-ion batteries, lithium has emerged as a critical environmental contaminant, yet the mechanisms of its toxicity and tolerance in plants remain poorly understood. This study investigates the physiological and molecular responses of the C4 model crop foxtail millet (Setaria italica) to LiCl stress. Physiological analyses revealed a concentration-dependent effect: while low Li⁺ levels activated the antioxidant system, exposure to 50 mg/L LiCl triggered a severe oxidative burst, leading to the suppression of antioxidant enzyme activities (SOD, POD, CAT), lipid peroxidation, and significant growth inhibition. Transcriptomic profiling of the cultivar “Jingu 21” identified 1562 commonly regulated differentially expressed genes, indicating that Li⁺ stress disrupts Na⁺/K⁺ homeostasis and reprograms metabolic pathways, including the upregulation of branched-chain amino acid degradation and plant-pathogen interaction pathways. To validate these findings, we analyzed five additional cultivars exhibiting differential tolerance. Comparative analysis demonstrated that the robust tolerance observed in “Jigu 22” correlated with the strong induction of key genes-specifically the transcription factor SiBHLH148, the vacuolar transporter SiNHX1, and the lipid transfer protein SiDIR1-suggesting their pivotal roles in maintaining ROS homeostasis and ion compartmentalization. These results elucidate the molecular basis of LiCl adaptation in foxtail millet and provide crucial genetic targets for breeding crops resilient to lithium pollution.