Atypical and probable non DNA-binding bHLH transcription factor that acts as negative regulator of cell elongation and plant development. Binds the transcription factor ILI1 and forms a heterodimer of antagonistic bHLH transcription factors that function downstream of BZR1 to mediate brassinosteroid regulation of cell elongation and lamina inclination (By similarity). Interacts with ILI1. Belongs to the bHLH protein family. Truncated N-terminus.