ZmILI1 confers salt stress tolerance by regulating genes of phytohormone response in maize

Salt stress is a major abiotic stress that has severe adverse effects on the growth, development, yield and quality of crop plants. Molecular regulatory mechanisms underlying salt stress response in maize are still elusive. Understanding salt stress tolerance mechanisms is essential for the development of high-yielding maize cultivars with improved salt tolerance. Here, we identified a gene, INCREASED LEAF INCLINATION1 (ZmILI1), encoding a bHLH transcription factor, which positively regulates maize response to salt stress. Salt stress induces the expression of ZmILI1, and the overexpression of ZmILI1 enhances catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) activities, thus enhancing salt stress tolerance. DNA affinity purification sequencing (DAP-Seq), RNA sequencing (RNA-Seq), dual-luciferase (LUC), yeast one hybrid, and Real-time polymerase chain reaction (RT-qPCR) assays revealed that ZmILI1 positively regulates salt stress response in maize by modulating the expression of the transcription factor family genes (ZmAP2-197), hormone-related genes (ZmLOX6, ZmDHN1, ZmCaDK2C) and antioxidant enzyme system-related genes (ZmPOD5), thus maintaining cellular homeostasis. Moreover, ZmILI1 is directly or indirectly implicated in maize response to salt stress by regulating the expression of genes involved in jasmonic acid (JA) biosynthesis, such as ZmLOX6, leading to elevated levels of JA hormone in maize under salt-stressed conditions. Our findings not only provide genetic evidence for the role of the bHLH protein family in agricultural production but also reveal potential regulatory mechanisms for the development of salt-tolerant genetic resources, offering new insights into the breeding of salt-tolerant maize varieties.