Genome wide identification, structural characterization, expression analysis, and regulatory network inferring of BAG gene family in barley.

The BAG (Bcl-2-associated athanogene) gene family plays a crucial role in plant stress responses by regulating programmed cell death, protein homeostasis and molecular chaperone interactions. While they have been extensively studied in model plants such as Arabidopsis and rice, the functional role and evolutionary dynamics of BAG genes in barley (Hordeum vulgare L.) are still largely unexplored. In this study, seven HvBAG genes were identified and characterised and their structural diversity, phylogenetic classification, chromosomal distribution and expression patterns were analysed. Comparative analyses with rice, maize, wheat and Arabidopsis revealed pedigree-specific expansions and conserved motifs underlining the functional importance of BAG proteins in stress adaptation. Our study revealed variations in protein stability, hydrophobicity and subcellular localisation, with HvBAG3 predominantly localised in the nucleus and HvBAG5 in the mitochondria, suggesting specialised cellular functions. Synteny and duplication analyses showed that segmental duplications and purifying selection have contributed to the expansion and evolutionary conservation of HvBAG genes. Expression profiling under heat stress revealed differential regulation in different tissues, with HvBAG3 significantly upregulated in roots and shoots, suggesting its role in heat stress resistance. Furthermore, miRNA-mediated regulation of HvBAG genes provides an additional level of post-transcriptional control that refines the mechanisms of stress response. This study provides a framework for understanding the functional diversity of BAG genes in barley and offers insights into their evolutionary history and regulatory mechanisms. These results have practical implications for the breeding of stress-resistant barley varieties and point to BAG genes as potential targets for genetic engineering strategies.