Comprehensive analysis of TGA genes in barley: structure, evolution, and stress-responsive expression

TGA transcription factors (bZIP family) are central to hormone signalling and stress responses in plants. However, their genomic organization and regulatory potential in barley (Hordeum vulgare L.) remain insufficiently characterised.

A total of 49 HvTGA genes were identified, which are unevenly distributed across the barley genome, with the most prominent clusters located on chromosomes 3 H and 5 H. Phylogenetic reconstruction divided the family into four clades supported by conserved bZIP domains, clade-specific motifs, and distinct exon-intron structures, suggesting both evolutionary conservation and functional diversification. Gene duplication analysis revealed that segmental and dispersed duplications are the dominant drivers of expansion, while Ka/Ks ratios < 1 indicate strong purifying selection maintaining functional stability. Promoter analysis revealed numerous cis-regulatory elements associated with ABA, SA, JA, osmotic stress, and light responses, with HvTGA-18, HvTGA-24, and HvTGA-35 carrying particularly dense clusters. Post-transcriptional regulation was supported by the prediction of 31 miRNAs targeting 29 HvTGAs, with hvu-miR6192 emerging as a key regulator of eight members. Protein-protein interaction networks based on Arabidopsis orthologues identified HvTGA-13, HvTGA-26, and HvTGA-28 as putative components of predicted regulatory interaction networks, interacting with NPR and GRX proteins, along with other stress-responsive transcription factors. Functional enrichment analysis further indicated that HvTGAs are involved in transcriptional regulation, hormone-mediated signalling cascades, MAPK signalling pathways, and carotenoid biosynthesis. Expression analysis of HvTGA genes across multiple abiotic stress conditions and tissues revealed distinct and dynamic transcriptional responses to heat, salt, and osmotic stress. Under heat stress, several HvTGA genes, including HvTGA-29, HvTGA-43, HvTGA-41, and HvTGA-38, were significantly up-regulated in both shoot and root tissues. In response to salt stress, HvTGA-29, HvTGA-12, HvTGA-14, HvTGA-21, and HvTGA-33 showed strong induction in root tissue, particularly at later time points. Notably, HvTGA-29, HvTGA-43, and HvTGA-41 exhibited consistent and robust induction across multiple abiotic stress conditions and tissues, supported by functional enrichment analysis, indicating their potential roles as central regulators within stress-responsive transcriptional networks in barley.

This first genome-wide characterisation of HvTGAs uncovers their structural diversity, evolutionary origins, and regulatory complexity, while highlighting HvTGA-29, HvTGA-43, and HvTGA-41 as key candidate regulators likely contributing to stress- and hormone-responsive networks in barley.