Genome-wide Identification, Evolution and Expression Analysis of Basic Helix-loop-helix (bHLH) Gene Family in Barley ( Hordeum vulgare L .).

Background The basic helix-loop-helix (bHLH) transcription factor is one of the most important gene families in plants, playing a key role in diverse metabolic, physiological, and developmental processes. Although it has been well characterized in many plants, the significance of the bHLH family in barley is not well understood at present. Methods Through a genome-wide search against the updated barley reference genome, the genomic organization, evolution and expression of the bHLH family in barley were systematically analyzed. Results We identified 141 bHLHs in the barley genome (HvbHLHs) and further classified them into 24 subfamilies based on phylogenetic analysis. It was found that HvbHLHs in the same subfamily shared a similar conserved motif composition and exon-intron structures. Chromosome distribution and gene duplication analysis revealed that segmental duplication mainly contributed to the expansion of HvbHLHs and the duplicated genes were subjected to strong purifying selection. Furthermore, expression analysis revealed that HvbHLHs were widely expressed in different tissues and also involved in response to diverse abiotic stresses. The co-expression network was further analyzed to underpin the regulatory function of HvbHLHs. Finally, 25 genes were selected for qRT-PCR validation, the expression profiles of HvbHLHs showed diverse patterns, demonstrating their potential roles in relation to stress tolerance regulation. Conclusion This study reported the genome organization, evolutionary characteristics and expression profile of the bHLH family in barley, which not only provide the targets for further functional analysis, but also facilitate better understanding of the regulatory network bHLH genes involved in stress tolerance in barley.