Drought stress induces morphophysiological adaptations and upregulates group A bZIP transcription factors in Triticum aestivum cultivar Excalibur

Abstract The basic leucine zipper domain (bZIP) transcription factor (TF) family is the largest TF family that plays a crucial role in plant stress responses. This family has been further classified into ten groups (A to I and S). Group A members predominantly play an important role in biotic and abiotic stress tolerance. In this study, we characterized the tolerant wheat cultivar Excalibur for drought stress response through morphological, biochemical, and molecular indices. Different traits like plant height, primary root length, root and shoot biomass, and photosynthetic pigments were determined. After a seven-day drought stress, cultivar Excalibur exhibited a decrease in plant height and shoot biomass. In contrast, primary root length and root dry biomass were significantly increased under drought stress. Moreover, drought stress induced a significant reduction in chlorophyll content; however, carotenoid contents were significantly higher compared with the control. Analysis of promoter cis-regulatory elements revealed a predominance of ABA- and drought/dehydration-responsive motifs, supporting the involvement of TabZIP genes in ABA-mediated abiotic stress responses. PPI network analysis indicated that all selected TabZIP proteins interact with SnRK2 and other serine/threonine kinases, suggesting their participation in phosphorylation-dependent stress signaling. GO and KEGG analyses consistently enriched these proteins in ABA-activated signaling, MAPK, and plant hormone signal transduction pathways. The expression of four bZIP genes ( TabZIP46 , TabZIP60 , TabZIP111 , TabZIP174 ) was significantly up-regulated under drought stress, demonstrating their functional significance under water deficiency in wheat. Overall, this study establishes Group A TabZIP transcription factors as key regulators of drought stress tolerance in wheat, offering valuable targets for the development of stress-resilient wheat varieties.