Ectopic expression of HvbHLH132 from hulless barley reduces cold tolerance in transgenic Arabidopsis thaliana

Key messageOverexpression of HvbHLH132 from hulless barley impairs in chilling and freezing tolerance at the seedlings stage in Arabidopsis thalianaAbstractThe basic helix-loop-helix (bHLH) transcription factors (TF) are ubiquitously existed in eukaryote and play crucial roles in numerous biological processes. However, the characterization of their members and functions in hulless barley remains limited. Here, we conducted a genome-wide identification of the HvbHLH gene family and assessed the role of HvbHLH132 in cold stress tolerance. We identified 141 HvbHLH genes, which were categorized into twelve subfamilies. Subcellular localization predictions indicated that the majority of HvbHLH proteins were localized in the nucleus. cis-Acting element analysis revealed that the promoter regions of the HvbHLH family contain diverse elements associated with various biological processes. Expression profiling of the 141 HvbHLH genes in two extreme varieties revealed that HvbHLH132 was significantly induced and exhibited substantial differential expression under cold stress. Analyses of subcellular localization and transactivation activity confirmed that HvbHLH132 specifically localized in the nucleus and contributed to transcriptional activation. Furthermore, overexpression of HvbHLH132 in Arabidopsis resulted in impaired chilling and freezing tolerance at the seedling stage, leading to biochemical changes unfavorable for freezing stress. Additionally, the expression of some cold-responsive genes (COR) genes was significantly less induced compared to wild type under freezing stress. This study provides comprehensive insight into the HvbHLH gene family and reveals a critical role of HvbHLH132 in regulating cold tolerance in plants.