Physiological and Transcriptome Analysis of Drought Tolerance in Barley

Drought stress is the major environmental constraint in crop production. As climate change increases drought frequency, enhancing drought tolerance has become a major goal in barley breeding. Hordeum vulgare ssp. spontaneum, the wild and closest relative of cultivated barley, is a valuable genetic resource for breeding and developing drought-tolerant cultivars. This study aimed to compare physiological and transcriptomic responses of a drought-tolerant wild genotype (H. vulgare ssp. spontaneum) and a drought-sensitive cultivated barley genotype (‘Mona’ cultivar) under control and drought stress conditions. The wild genotype exhibited less physiological and growth impairment than the ‘Mona’ cultivar under drought stress. Transcriptome profiling identified 2564 differentially expressed genes (DEGs) in the drought-tolerant wild genotype and 2163 DEGs in the drought-sensitive cultivar. Notably, in the tolerant genotype, most DEGs were up-regulated, whereas in the sensitive cultivar, down-regulation was more frequently induced by drought. GO enrichment analysis revealed that the DEGs were predominantly associated with key stress-related biological processes, including cellular component organization, signaling pathways, ion transport, regulatory protein activity, reactive oxygen species (ROS) scavenging, hormone biosynthesis, and osmotic homeostasis. Comparative analysis showed that the drought-tolerant genotype harbored more functionally effective drought-responsive genes and had higher transcript abundance than the sensitive genotype. Overall, the tolerant genotype consistently exhibited superior physiological and functional performance under drought stress. These findings deepened our understanding of the evolutionary basis of drought tolerance in wild barley, while the shared functional mechanisms between the two subspecies identified physiological and transcriptional traits that could be exploited to improve barley under water-limited environments.