Physiological and transcriptomic insights into the molecular mechanisms of salt stress adaptation in Gardenia jasminoides

Salt stress is a major environmental factor limiting plant growth and productivity. Plants have developed diverse physiological and molecular strategies to adapt to saline conditions. Gardenia jasminoides, a dual-purpose plant with significant economic value in medicine and landscaping, exhibits notable salt tolerance, but the underlying molecular mechanisms remain largely unexplored. Our study aims to elucidate the physiological and molecular adaptive strategies of this plant to salt stress by integrating physiological measurements and transcriptomic analysis. RNA-seq profiling of G. jasminoides leaves, which were subjected to four NaCl concentrations (0, 50, 100, and 200 mmol·L⁻¹) for 15 days, identified 3,883 differentially expressed genes (DEGs). These DEGs were mainly associated with calcium signaling, MAPK–WRKY cascades, antioxidant defense, and phytohormone regulation. Physiological analysis revealed that prolonged stress caused structural damage to the photosynthetic apparatus, evidenced by a significant decline in Fv/Fm and an increase in Fo at Day 15. These changes mirrored transcriptional reprogramming: peroxidase (POD) activity and related genes were strongly induced, catalase (CAT) activity was repressed, and malondialdehyde (MDA) levels increased under severe stress. Osmotic adjustment displayed stress-dependent patterns, with proline accumulation peaking under moderate stress and soluble proteins under severe stress. Network analysis highlighted a hierarchical regulatory system, where calcium signaling and MAPK cascades coordinated antioxidant defense and ion homeostasis. Key salt-responsive regulators, including CaM/CML, CDPK, WRKY22/29, and glutathione S-transferase (GST) family members, were proposed as central nodes integrating Ca²⁺ influx, reactive oxygen species (ROS) production, MAPK activation, and abscisic acid (ABA) signaling. Our findings reveal a hierarchical regulatory network that fine-tunes ROS homeostasis, osmotic balance, and stress signaling in G. jasminoides. Salt-responsive regulators such as WRKY transcription factors and GST family members represent promising targets for functional studies and molecular breeding aimed at enhancing salt tolerance in woody plants for ecological restoration and agricultural production.