Comprehensive analysis of salt tolerance mechanisms in forage maize: physiological adaptation, transcriptional regulation, and key gene identification

Soil salinization severely restricts the growth of forage maize (Zea mays L.), yet the physiological and molecular mechanisms underlying salt tolerance in domestic forage maize varieties remain unclear. This study aimed to identify salt-tolerant germplasm and reveal key regulatory pathways associated with salt stress responses. Thirty forage maize varieties were evaluated under gradient salt stress treatments during germination. Based on comprehensive membership function analysis, two contrasting varieties were identified: the salt-tolerant Jinling Silage 377 and the salt-sensitive Tieyan 53. Physiological assays showed that the tolerant variety maintained higher SOD and POD activities and greater accumulation of soluble proteins and sugars under high salt stress, suggesting enhanced osmotic adjustment and antioxidant defense. Transcriptome analysis revealed 3,168 and 5,211 differentially expressed genes (DEGs) in the tolerant and sensitive varieties, with 2,061 DEGs shared between them. Key salt-responsive genes (PYR/PYL, SnRK2, CAT1, MPK4, MPK6) were significantly upregulated in the tolerant genotype, mainly in hormone signaling and MAPK pathways. Several transcription factor families—especially AP2/ERF-ERF, bHLH, and WRKY—were enriched, and qRT-PCR validated their expression patterns. Notably, the common differentially expressed genes AP2/EREBP-143 and ZmWRKY93 were significantly upregulated in salt-tolerant varieties and under salt stress, suggesting their potential role in salt tolerance through synergistic actions and network regulation.