InterPro domain: IPR044549

This entry represents the bHLH domain found in a group of transcription factors from plants, including IBH1 (ILI1-BINDING BHLH 1), IBHL1 and related proteins such as UPBEAT1, PAR1 and PAR2 from Arabidopsis. IBH1 (also known as AtbHLH158) and IBHL1 are atypical and probable non DNA-binding bHLH transcription factors that act as transcriptional repressors that negatively regulate cell and organ elongation in response to gibberellin (GA) and brassinosteroid (BR) signaling [ 1 , 2 ]. IBH1 forms heterodimer with BHLH49, thus inhibiting DNA binding of BHLH49. Another atypical transcription factors included in this entry are PAR1 (also termed AtbHLH165) and PAR2 (also termed AtbHLH166) that act as negative regulators of a variety of shade avoidance syndrome (SAS) responses [ 3 , 4 ]. UPBEAT1 (also known as AtbHLH151 or EN 146), modulates the balance between cellular proliferation and differentiation in root growth [ 5 ].

1. Helix-loop-helix/basic helix-loop-helix transcription factor network represses cell elongation in Arabidopsis through an apparent incoherent feed-forward loop. Proc Natl Acad Sci U S A 111, 2824-9
2. Regulation of Arabidopsis brassinosteroid signaling by atypical basic helix-loop-helix proteins. Plant Cell 21, 3781-91
3. Interaction of shade avoidance and auxin responses: a role for two novel atypical bHLH proteins. EMBO J 26, 4756-67
4. The shade avoidance syndrome in Arabidopsis: a fundamental role for atypical basic helix-loop-helix proteins as transcriptional cofactors. Plant J 66, 258-67
5. Transcriptional regulation of ROS controls transition from proliferation to differentiation in the root. Cell 143, 606-16