Salinity signaling networks in wheat: crosstalk among Ca2⁺, ROS, phytohormones, and metabolic signals in salt adaptation
Abstract Soil salinity limits wheat productivity by disrupting water uptake, Na⁺/K⁺ homeostasis, photosynthesis, reproductive development, and grain filling. Although wheat salinity tolerance is often discussed in terms of individual traits such as Na⁺ exclusion, antioxidant defense, osmolyte accumulation, or abscisic acid signaling, these responses operate as interconnected signaling networks. This review reframes wheat salinity adaptation as a crosstalk-driven process linking early root perception with whole-plant acclimation and yield-related outcomes. At the root-soil interface, salinity rapidly lowers external water potential, alters membrane potential, disturbs ion fluxes, and induces early Ca2⁺, reactive oxygen species (ROS), pH, nitric oxide, electrical, and phosphorylation signals. Ca2⁺ sensors and decoders, including CaM/CMLs, CDPKs, and CBL-CIPK modules, connect these early signals with ROS regulation, ion-transporter activity, kinase cascades, and transcriptional reprogramming. ABA integrates osmotic stress with stomatal closure, hydraulic adjustment, compatible-solute accumulation, and water-use regulation, whereas additional hormonal and metabolic signals shape root architecture, growth restraint, senescence, source-sink balance, and reproductive protection. Wheat-specific evidence strongly supports the importance of HKT1;5-mediated Na⁺ retrieval, SOS-like ion regulation, K⁺ retention, antioxidant capacity, ABA-associated water regulation, osmotic adjustment, and genotype-dependent transcriptional responses. However, several important signaling models, including precise Ca2⁺ signatures, real-time Ca2⁺-ROS feedback dynamics, guard-cell ABA-ROS-Ca2⁺ signaling, systemic Ca2⁺/ROS waves, and salinity-specific sugar-redox-hormone control of grain filling, remain incompletely validated in wheat. By distinguishing wheat-supported mechanisms from conserved model-plant frameworks, this review identifies key signaling hubs and physiological trade-offs that may guide breeding, genome editing, priming, and agronomic strategies for improving wheat performance under saline environments.