Genome-wide characterization of the Bcl-2-associated athanogene (BAG) gene family and functional analysis of ZmBAG14 under drought stress in maize

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Drought imposes one of the most damaging constraints on maize productivity, particularly during critical developmental period such as flowering and pollination, when water deficit most severely disrupts normal plant growth. The Bcl-2-associated athanogene (BAG) proteins constitute a highly conserved co-chaperone family whose members participate in extensive biological processes, ranging from developmental regulation to adaptive responses under abiotic stress. In the present study, a comprehensive genome-wide characterization of the maize (Zea mays L.) reference genome (Zm-B73-REFERENCE-NAM-4.0) identified 24 ZmBAG genes, named ZmBAG1–24, which were classified into seven distinct phylogenetic groups. All identified proteins share a conserved BAG domain, while subsets additionally carry either a ubiquitin-like (UBL) domain or a plant-specific isoleucine-glutamine (IQ) calmodulin-binding motif positioned toward the N-terminus. Promoter analysis of ZmBAGs uncovered an abundance of stress-responsive regulatory elements were present, pointing to this gene family in ABA-mediated and drought-responsive transcriptional programs. Further transcriptional profiling under drought-stress conditions revealed divergent expression characteristics among family members, indicating that individual ZmBAGs contribute differentially to the drought stress. Among them, ZmBAG14 showed lower expression under drought stress, compared to the control (well-watered). Functional characterization using bag14 EMS mutants demonstrated that diminished ZmBAG14 expression correlated with reduced reactive oxygen species (ROS) accumulation in stomatal guard cells and water loss rate, elevated activities of peroxidase (POD) and superoxide dismutase (SOD), and ultimately enhanced drought tolerance and yield improvements. Protein interaction studies further revealed that ZmBAG14 interacts with the inward-rectifying potassium channel ZmKZM2, which influences stomatal movement by modulating K + influx in guard cells under drought stress. Together, these findings provide a new perspective for genome-wide identification and functional utilizing of ZmBAG genes to improve drought tolerance in maize.