Atypical bHLH transcription factor that acts as negative regulator of grain size. Binds the transcription factor ILI6 and forms a heterodimer of antagonistic bHLH transcription factors that regulates grain length and weight by controlling cell elongation in lemma and palea. May be involved in the control of lamina inclination through brassinosteroid signaling pathway. Homodimer and heterodimer with ILI5 or ILI6. Plants silencing APG show enhanced bending of the lamina joints and produce grains increased in size, caused by elongated cells in lemma. Belongs to the bHLH protein family. Sequencing errors.