Characteristics of bHLH transcription factors and their roles in the abiotic stress responses of horticultural crops

Abiotic stresses are major environmental factors that affect crop growth, productivity and quality. The bHLH family is one of the largest transcription factor (TF) families in plants, playing important roles in many different response pathways of diverse abiotic stresses, such as water deficit, high salinity, low temperature, and nutrient deficiencies. Since the discovery of the bHLH family in plants, many studies in model plants have explored the roles and regulatory mechanisms of bHLH family members in abiotic stress response. In recent years, the bHLH TFs have been extensively studied in the regulation of abiotic stress response and resistance in horticultural crops. A review of these studies can provide insights and directions for the study of abiotic stress response in horticultural crops. Here, we summarize the structure, classification and regulation of bHLH TFs, and focused on the function and regulatory mechanisms of key bHLH TFs in the abiotic stress response of horticultural crops. Several key bHLH proteins that bridge different signaling pathways in abiotic stress response were described in detail, such as ICE1, FER, PIFs, and several Ib and IVc bHLHs. This review will provide a theoretical basis for further studies on the regulation of bHLH TFs in the abiotic stress response and the yield and quality of horticultural crops under stressed conditions. It will also provide resources for stress-resistant breeding of horticultural crops using transgenic technology.