INTEGRATIVE PHYSIOLOGICAL AND TRANSCRIPTOMIC ANALYSIS REVEALS DROUGHT ADAPTATION MECHANISMS IN WHEAT UNDER CLIMATE STRESS

Abstract

Drought is a major constraint on wheat productivity, yet drought tolerance is an emergent trait generated by coordinated changes in water status, photosynthetic regulation, osmotic adjustment, redox homeostasis, and gene expression. This study used an integrative physiological–transcriptomic framework to compare two contrasting bread-wheat lines under progressive water deficit. Plants of a drought-tolerant line (DT-01) and a drought-sensitive line (DS-01) were maintained at 80% field capacity (well-watered), 50% field capacity (moderate drought), or 30% field capacity (severe drought). Leaf relative water content, chlorophyll status, gas exchange, biomass, compatible solutes, oxidative-damage markers, and antioxidant enzymes were quantified. RNA sequencing was conducted on control and severe-drought leaf samples. Severe drought reduced relative water content, net photosynthesis, and biomass in both genotypes, but DT-01 retained 81%, 59%, and 71% of its well-watered values, respectively, compared with 67%, 35%, and 55% in DS-01. DT-01 accumulated more proline and soluble sugars and showed stronger superoxide dismutase, catalase, and peroxidase activities, while maintaining lower malondialdehyde and hydrogen peroxide. Transcriptome profiling identified 3,842 drought-responsive genes in DT-01 and 5,967 in DS-01. The tolerant line preferentially activated ABA signaling, dehydrins, osmoprotectant biosynthesis, membrane transport, and reactive-oxygen-species detoxification, whereas the sensitive line displayed broader suppression of photosynthetic and growth-related programs together with stronger stress-injury signatures. Multivariate integration separated genotype-by-water-regime combinations and linked physiological resilience to coordinated expression of TaNCED1, TaSnRK2.4, TaDREB2, TaDHN4, TaP5CS1, and antioxidant genes. The results support a model in which drought adaptation in wheat depends less on the magnitude of stress-induced transcription alone than on targeted transcriptional reprogramming that preserves water balance, limits oxidative injury, and sustains photosynthetic function.