Stress-Inducible Expression of HvABF2 Transcription Factor Improves Water Deficit Tolerance in Transgenic Barley Plants

Barley (<i>Hordeum vulgare</i> 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 <i>HvABF2</i> gene, encoding an ABA-dependent transcription factor, was cloned using specific primers from water deficit-stressed barley seedlings. Gene expression analysis revealed high <i>HvABF2</i> expression in developing caryopses and inflorescences, with significant induction under stress conditions. The <i>HvABF2</i> coding sequence was utilized to generate transgenic barley plants with both stress-inducible and constitutive expression, driven by the rice <i>SNAC1</i> and maize <i>Ubiquitin</i> 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 <i>HvABF2</i> 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 <i>HvABF2</i>, using the <i>SNAC1</i> promoter, effectively improves drought tolerance while avoiding the negative pleiotropic effects observed with constitutive expression.