Genome-wide analysis of the DREB gene family and functional characterization of HaDREB1D in the drought stress response in sunflower (Helianthus annuus L.)

Sunflower (Helianthus annuus L.), an important global oilseed crop, demonstrates remarkable tolerance to drought and salinity. Among transcription factors, dehydration-responsive element-binding (DREB) proteins are broadly distributed in plants and play pivotal roles in regulating abiotic stress responses. In this study, a total of 62 DREB genes were identified in sunflower and classified into five subgroups based on phylogenetic relationships, with 59 genes mapped to 16 chromosomes. Cis-acting element analysis indicated that HaDREB genes are primarily associated with stress responsiveness, phytohormone signaling, and light-regulated pathways, underscoring their functions in environmental adaptation and abiotic stress tolerance. Transcriptome analysis revealed that numerous HaDREB genes exhibited differential expression under drought, salinity, and cold stress, suggesting diverse and condition-specific regulatory roles. Furthermore, expression profiling across seed developmental stages demonstrated that most of the 31 detectable HaDREB genes were highly expressed during the middle and late stages of seed development, implying potential regulatory contributions to seed formation and maturation. Functional validation of HaDREB1D through overexpression in transgenic Arabidopsis thaliana confirmed its role in enhancing drought tolerance. Compared with wild-type plants, transgenic lines showed significantly higher survival rates and improved physiological performance after 14 days of drought treatment followed by 4 days of rewatering. This study provides the first experimental evidence that HaDREB1D contributes to drought stress tolerance in sunflower, establishing a foundation for future functional investigations of HaDREB genes in abiotic stress adaptation.