PROSiCAPE14 regulates salt tolerance through ROS and ion homeostasis in foxtail millet

Soil salinization is a major abiotic stress threatening global agricultural sustainability, making the utilization of saline-alkaline land critical for food security. Foxtail millet (Setaria italica), an ancient crop adaptable to arid and marginal soils with a robust root system, serves as both a strategic reserve crop for harsh climates and a model plant for C4 functional genomics research. However, the molecular mechanisms underlying foxtail millet's salt tolerance remain poorly understood, limiting its genetic improvement. This study investigated the CAPE gene family and identified PROSiCAPE14 as a key salt-responsive gene, which is downregulated under salt stress. Both exogenous application of its encoded peptide and transgenic overexpression led to compromised growth under salt stress compared to wild-type plants. Under salt stress, overexpression lines exhibited significantly reduced plant height and root length along with elevated sodium ion accumulation compared to controls. Furthermore, DAB and NBT staining indicated a deeper coloration in the overexpression lines, suggesting higher reactive oxygen species accumulation. Subsequent yeast one-hybrid assays and dual-luciferase reporter assay further verified that the transcription factors SibHLH49 and SiMYBS1, which play important roles in salt stress response, can interact with the promoter of the PROSiCAPE14 gene, regulating its expression. This further supports the hypothesis that PROSiCAPE14 plays a significant role in the salt stress response of foxtail millet. This research provides a foundation for further investigation into the roles of CAPE genes in abiotic stress adaptation and other potential biological functions in foxtail millet.