WUSCHEL-Related Homeobox Gene-Mediated Regulation of Salt Tolerance in Sour Jujube: Role of the ZjWOX6–ZjCKX8 Module

Sour jujube originates from China and is highly valued for its economic and medicinal importance. However, its growth and cultivation are frequently constrained by salt stress, which severely limits productivity. The WUSCHEL-related homeobox (WOX) gene family plays crucial roles in plant development and responses to environmental stresses. Despite their importance, the functions of sour jujube WOX genes (ZjWOXs) under salt stress remain largely unexplored. Here, transcriptome analysis revealed that ZjWOX6 was significantly induced by salt stress compared with other ZjWOXs family members. Subcellular localization analysis indicated that ZjWOX6 was localized to both the cell membrane and the nucleus. To investigate its biological function, a stable genetic transformation system based on a leaf shoot regeneration method was established in sour jujube. Overexpression of ZjWOX6 markedly enhanced salt tolerance, whereas transient silencing of ZjWOX6 increased salt sensitivity. Further analyses showed that ZjWOX6 directly bound to the promoter region of cytokinin oxidase/dehydrogenase 8 (ZjCKX8), a key gene involved in cytokinin metabolism, and negatively regulated its expression, thereby modulating salt tolerance in sour jujube. Collectively, these findings provide important molecular insights into the role of ZjWOX6 in the salt stress response and offer a valuable foundation for the development of salt-tolerant sour jujube cultivars through genetic and biotechnological breeding strategies.