Abstract
Barley (Hordeum vulgare L.), a major cereal crop grown in arid and semi-arid regions, faces significant yield variability due to drought and heat stresses. In this study, the HvABF2 gene, encoding an ABA-dependent transcription factor, was cloned using specific primers from water deficit-stressed barley seedlings. Gene expression analysis revealed high HvABF2 expression in developing caryopses and inflorescences, with significant induction under stress conditions. The HvABF2 coding sequence was utilized to generate transgenic barley plants with both stress-inducible and constitutive expression, driven by the rice SNAC1 and maize Ubiquitin promoters, respectively. Selected transgenic barley lines, along with control lines, were subjected to water deficit-stress experiments at seedling and flag leaf stages under controlled and greenhouse conditions. The transgenic lines exhibited higher relative water content and stomatal resistance under stress compared to control plants. However, constitutive overexpression of HvABF2 led to growth retardation under well-watered conditions, resulting in reduced plant height, grain weight, and grain number. In contrast, stress-inducible expression mitigated these effects, demonstrating improved drought tolerance without adverse growth impacts. This study highlights that the stress-inducible expression of HvABF2, using the SNAC1 promoter, effectively improves drought tolerance while avoiding the negative pleiotropic effects observed with constitutive expression.