bHLH Transcription Factors in Cereal Crops: Diverse Functions in Regulating Growth, Development and Stress Responses

Basic helix-loop-helix (bHLH) transcription factors represent one of the largest transcriptional regulator families in cereal crops such as rice, maize, and wheat. They play crucial and diverse roles in regulating key agronomic traits and essential physiological processes. This review provides a systematic synthesis of the functionally characterized bHLH genes across the three major cereals, offering a comparative perspective on their roles in growth, development, and stress responses. We comprehensively summarize their documented functions, highlighting specific regulators such as TaPGS1 for grain size, rice ILI subfamily for leaf angle, OsbHLH004 for seed dormancy and maize "Ms23-Ms32-bHLH122-bHLH51" cascade for the anther development. Their conserved and species-specific functions in iron homeostasis (e.g., IRO2) and in responses to drought, cold, salinity, and pathogens are also detailed. Additionally, we discuss the underlying molecular mechanisms, including specific binding to E-box/G-box cis-elements, protein dimerization, and integration with hormone signaling pathways. By integrating the current knowledge, this review serves as a consolidated and up-to-date reference that highlights the strategic potential of bHLH transcription factors in molecular breeding programs for improving yield, quality, and stress tolerance in cereals.