Wheat (Triticum aestivum L.) stands as a significant cereal crop within the Poaceae family, playing a vital role in contributing to around 30% of the global food production (Akter et al., 2017). It is widely regarded as the "king of cereals" and serves as a staple crop for one-third of the world's population. Wheat grains are rich in essential nutrients, including 8–17% protein, 60–80% carbohydrates (primarily starch), 1.5-2% lipids,1.5-2% minerals, 2.2% crude fibers, and vitamins (B-complex and E), as well as all essential amino acids (Ahmed et al. 2020; Shewry et al. 2015). In response to the rapidly growing global population, it is necessary to achieve a twofold increase in wheat production by 2050 (FAO, 2021).
Various abiotic stresses including drought stress, heat stress, chilling injury, and salinity stress, exert a significant influence on the global wheat yield and grain quality (Kumar et al. 2021). Among these stresses, drought stress and heat stress pose major challenges to wheat production and global food security. Drought stress has detrimental effects on wheat growth, such as reduced leaf surface area, decreased mobilization of reserves, kernel abortion and a decreased quantity of amyloplasts in grains (Qaseem et al. 2019). Heat stress negatively affects the crop cycle, resulting in abortion of pollen, kernel shrinkage, reduced seed reserves, anther indehiscence and impaired pollen tube development, all of which contribute to decreased crop yield (Kumar et al. 2021). Drought stress and heat stresses significantly diminish leaf area, photosynthetic efficiency, stomatal conductance and water-use efficiency. Heat stress can lead to increased evapotranspiration, ultimately causing plants to experience drought stress, thereby severely affecting the water relations of the crops (Lamaoui et al. 2018). The reproductive phases of wheat display increased vulnerability when exposed to the simultaneous impacts of heat and drought stress. It has been predicted that the global production of wheat may decrease by 5.5% due to the impact of these two stresses (Lobell et al. 2015). Furthermore, it is approximated that a rise of 1°C in temperature leads to a 6% drop in worldwide wheat production (Ahmad et al. 2020)
Transcription factors (TFs) play pivotal roles in regulating gene expression and coordinating complex physiological and biochemical responses to environmental stresses. One such important TF family involved in response to drought stress is the Dehydration-Responsive Element-Binding Protein (DREB) family. DREB TFs belong to the AP2/ERF (APETALA2/Ethylene Response Factor) superfamily and specifically bind to the conserved cis-acting DRE/CRT (Dehydration-Responsive Element/C-Repeat) motif present in the promoter regions of drought-responsive genes (Cao et al. 2020). The binding of DREB proteins to DREs results in the initiation of downstream genes i.e., regulation of stomatal closure to mitigate water loss through transpiration, the production of osmoprotectants such as proline and sugars to uphold cellular osmotic balance and the triggering of genes linked to antioxidant defense systems for countering oxidative stress induced by drought conditions (Singh et al. 2021). As a result, DREB proteins play a pivotal role in enhancing a plant's tolerance to drought stress by enabling water conservation, maintaining cellular homeostasis, and mitigating the adverse effects of drought on growth and development, as supported by studies conducted by (Usman et al. 2023). DREB transcription factors (TFs) have been identified in various plant species, such as Arabidopsis (Sharoni et al., 2011), barley (Xue, 2002), soybean (Mizoi et al., 2013), Rice (Nakano et al., 2006), maize (Qin et al., 2007), potato (Bouaziz et al., 2013) and others.
DREB TFs were categorized into six distinct subgroups (A1-A6) or DREB1 to DREB6 and members within distinct subgroups are involved in addressing diverse abiotic stress conditions (Niu et al., 2020). Among these groups, the transcription factors (TFs) falling under A-1 and A-2 have been extensively studied in terms of their functionality. DREB1 TFs primarily play a role in regulating cold stress. DREB2 genes play crucial roles in reacting to both drought and elevated salt stresses (Chen et al., 2016). While wheat stands as a predominant cereal crop globally, there is a limited number of functionally characterized wheat DREBs at present.
In present investigation, we identified, cloned and characterized putative DREB TF and studied the expression patterns of the identified DREB TF in different wheat genotypes and evaluated the effect of drought and heat stress on physiological parameters related to carbon assimilation and defense responses in wheat.