Basic helix-loop-helix/helix-loop-helix (bHLH/HLH) transcription factors play substantial roles in plant cell elongation. In this study, two bHLH/HLH homologous proteins leaf related protein 1 and leaf-related protein 2 (AtLP1 and AtLP2) were identified in Arabidopsis thaliana. LP1 and LP2 play similar positive roles in longitudinal cell elongation. Both LP1 and LP2 overexpression plants exhibited long hypocotyls, elongated cotyledons, and particularly long leaf blades. The elongated leaves resulted from increased longitudinal cell elongation. ...
