Functional Characterization of TaSnRK2.8-5A Reveals the Central Role of Its Signal Module in Enhancing Drought Tolerance Through Coordinated Molecular and Physiological Response of Wheat

Sucrose non-fermenting-1 (SNF1)-related protein kinase 2 (SnRK2) members are central regulators in the abscisic acid signaling pathway and orchestrate plant drought stress responses. However, the functional diversity and mechanistic specificity among SnRK2 family members in wheat remain underexplored. This study reports TaSnRK2.8-5A, a nucleus-localized SnRK2 member in wheat ( Triticum aestivum L.), whose transcription level was significantly upregulated under 12-hour drought stress, with a 2.6-fold increase in leaves and 3.6-fold increase in roots compared with control conditions ( P < 0.05), indicating its prominent role in stress signaling. Protein-protein interaction analysis revealed that TaSnRK2.8-5A interacts with TaPP2C53-1A and TabZIP23-6D, forming a novel ABA signaling module that distinguishes it from previously characterized SnRK2 members in wheat, which typically function through distinct or broader partners. Overexpression of TaSnRK2.8-5A or TabZIP23-6D alleviated drought-induced growth inhibition, whereas TaPP2C53-1A acted as a negative regulator. Under drought treatment, TaSnRK2.8-5A -OE, TabZIP23-6D -OE, and TaPP2C53-1A -KO lines displayed plant biomass increases of 32-42% compared with wild type plants. Physiological analyses demonstrated that these transgenic lines showed improved photosynthetic efficiency (net photosynthetic rate increased by 41%), enhanced osmolyte accumulation (proline increased by 14-25%; soluble sugars increased by 20-40%; soluble protein increased by 12-25%), and maintained ROS homeostasis (MDA reduced by 10-19%; SOD activity increased by 16.7-22%) under drought conditions ( P < 0.05). These results indicated that the TaPP2C53-1A/TaSnRK2.8-5A/TabZIP23-6D module integrates multiple physiological processes to coordinately enhance drought tolerance in wheat. Mechanistically, yeast one-hybrid and transcriptional activation assays indicated that TabZIP23-6D binds to the promoters of TaPIN1 , TaP5CS4 , and TaPOD2 , thereby activating their expression under drought stress. This regulation enhances root activity, proline biosynthesis, and ROS scavenging, respectively. Through the screening of a large wheat germplasm collection, the specific haplotype TaSnRK2.8-5A-Hap1 was identified as conferring superior drought tolerance. Collectively, these findings establish that a signal module centered on TaSnRK2.8-5A enhances the response of wheat to drought stress in coordination with physiological processes, providing both mechanistic insights into SnRK2-mediated drought adaptation and valuable gene resources for molecular breeding of drought-tolerant wheat cultivars. • TaSnRK2.8-5A is rapidly induced by drought stress, and its overexpression significantly enhances drought resistance in wheat. • TaSnRK2.8-5A interacts with TaPP2C53-1A and TabZIP23-6D to form a regulatory module (TaPP2C53-1A/TaSnRK2.8-5A/TabZIP23-6D) that coordinates the drought response by integrating key osmotic stress-related physiological pathways. • TabZIP23-6D enhances drought adaptation in wheat by binding to the promoters of downstream genes, thereby promoting root development, proline accumulation, and reactive oxygen species scavenging capacity.