Multifaceted role of SOS3 in regulating plant development and salinity tolerance

Salt stress is a major abiotic factor that limits plant productivity. Plants have evolved sophisticated signaling networks to resist salinity, with the salt overly sensitive (SOS) pathway playing a central role in maintaining ion homeostasis. In this pathway, the calcium-binding protein SOS3 (CBL4) acts as a primary calcium sensor, translating transient cytosolic Ca²⁺ signals into phosphorylation cascades that regulate Na⁺ extrusion and K⁺ retention. In addition to its role in salt stress, SOS3 influences diverse developmental processes, including root and shoot architecture, flowering time, and seed germination, through crosstalk with several signaling pathways, such as abscisic acid, reactive oxygen species, and MAPKs. SOS3 also promotes the activation of SOS1 and negatively regulates the protein stability of HKT1, two key Na⁺ transport systems in roots and shoots. Recent advances in Arabidopsis and major crops, such as rice, tomato, and cotton, have deepened our understanding of the SOS3 regulatory network, paving the way for the engineering of salt-tolerant cultivars. In this review, we summarize current insights into SOS3-mediated signaling, emphasizing its dual roles in plant development and adaptive stress responses, and discuss future directions for enhancing crop resilience through manipulation of SOS3 signaling.