The wheat basic helix-loop-helix (bHLH) protein TabHLH123 positively regulates the formation of crown root and associates with plant height and 1000-grain weight in wheat under various conditions.

Crown roots are the main components of the fibrous root system in cereal crops and play critical roles in plant adaptation. However, the molecular mechanisms of crown root formation in wheat (Triticum aestivum L.) have not been fully elucidated. Here, we identified a wheat basic helix-loop-helix (bHLH) protein TabHLH123, which interacts with the essential regulator of crown root initiation, MORE ROOT in wheat (TaMOR). It is expressed highly in shoot bases and roots. Ectopic expression of TabHLH123 in rice exhibits more roots compared with wild type. TabHLH123 regulates the expression of genes controlling crown root development, auxin metabolism, response and transport. Moreover, we analyzed the nucleotide sequence polymorphisms of TabHLH123s in wheat genome. The superior haplotype of TabHLH123-6B with high root dry weight (RDW) and 1000-grain weight (TGW), and short plant height (PH) was identified. Our study highlights the role of TabHLH123 in regulating the crown root formation and puts a novel insight for molecular marker assisted breeding in wheat.