Figure 3.

ATypical bHLH Transcription Factor in BR-Regulated Growth.

(A) All six members of the PRE family of atypical bHLH transcription factors rescue the dwarf phenotype, altered leaf shape, and shortened petioles of the weak bri1-301 mutant allele when overexpressed, indicating a positive role in BR signaling.

(B) Overexpression of the AIF1 bHLH transcription factor in wild-type Arabidopsis results in an extreme dwarf phenotype, suggesting that AIF1 is a negative regulator of BR signaling. The extent of the phenotype is correlated with the level of transgene expression. (Adapted with permission from Figures 4 and 7 of Wang et al. [2009].)