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. Author manuscript; available in PMC: 2011 Oct 1.
Published in final edited form as: Curr Opin Plant Biol. 2010 Sep 17;13(5):540–547. doi: 10.1016/j.pbi.2010.08.007

Figure 2.

Figure 2

The involvement of bHLH proteins and TFs of other families in BR signaling. (A). In Arabidopsis, BR induces AIF1 and PRE1 but inhibits ATBS1 and AtIBH1 with BZR1 binding to both PRE1 and AtIBH1 promoters. ATBS1 binds AIF1, thus inhibiting AIF1 dimerization with yet to be discovered bHLH proteins (X) that activate a subset of BR-responsive genes, while PRE1 heterodimerizes with AtIBH1 that functions as a negative regulator of BR-mediated cell elongation. BR also induces the expression of TCP1, which encodes a non-canonical bHLH protein that binds and activates the DWF4 promoter to stimulate BR biosynthesis, and stimulate the AtMYB30 gene, a directly target of BES1. BES1 was shown to interact with AtMYB30 on the promoters of some BR-responses genes to amplify BR signaling. (B). In rice, BR induces BU1 and ILI1 but suppresses IBH1 and DLT with OsBZR1 binding to the promoters of ILI1, IBH1, and DLT. ILI1 heterodimerizes with and thus inhibits IBH1 that blocks BR signaling; while DLT promotes BR signaling and plays a role in feedback regulation, likely by activating BR-upregulated genes and OsBZR1. The BR signaling in rice might also be negatively regulated by three SVP-type MADS proteins that likely localize in the cytosol [60].