Comparative analyses of the double B-box transcription factors in wheat pinpoints candidate TaDBBs associated with...

Double B-box (DBB) proteins, a plant-specific subgroup of the B-box (BBX) transcription factors, have been implicated in light signaling and stress responses. However, their evolutionary trajectory and functional divergence remain unexplored in the common wheat (Triticum aestivum L.), hindering the identification of stress-involved TaDBB candidates and the stress-responsive gene networks. Here, we performed a genome-wide identification and comparative analysis of DBB genes across 10 Poaceae species, with a focus on wheat and its relatives. Phylogenetic and duplication analysis, and expression profiling were integrated to re-construct the evolutionary patterns and to pinpoint the stress-responsive roles of several DBB genes. Candidate TaDBBs were further validated through qRT-PCR, protein subcellular localization, and transactivation assays. A total of 136 DBB genes were identified, including 29 TaDBBs from the common wheat genome forming nine triads. Dispersed duplication was the primary driver of DBB expansion in Triticeae. Expression profiling revealed that DBB genes exhibit tissue-specific and stress-responsive expression patterns. Notably, TaDBB4.1 and TaDBB4.2, derived from segmental duplication, showed divergent regulatory roles under saline/alkaline stress. TaDBB4.1 was found to negatively regulate photosynthesis-related genes, while TaDBB4.2 targeted ion transport and redox processes. Both localized to the nucleus and exhibited distinct transactivation activities. This study provides the first comprehensive analysis of DBB genes in wheat and highlights TaDBB4 as a key regulator of saline-alkaline stress responses. Our findings offer valuable genetic resources for improving wheat stress tolerance through molecular breeding.