The bHLH3 and bHLH17 antagonize TT8/MYB75 and MYC2 to negatively regulate their downstream target genes.

<p>(A) The schematic diagram shows the constructs used in the transient transcriptional activity assays of (B) and (C). (B) Transient transcriptional activity assays show that activation of <i>DFR</i> promoter by TT8/MYB75 is repressed by bHLH17 in dosage-dependent manner. The <i>P_DFR-LUC</i> reporter was cotransformed with the indicated constructs. The 0.2, 1, 5 or 10 µg bHLH17 (H17) plasmid DNA were respectively used for co-transformation with TT8 (T8) and MYB75 (M75). Numbers on the brackets indicate the relative values of the LUC/REN ratio of TT8/MYB75 with bHLH17 to that of TT8/MYB75. The LUC/REN ratio represents the <i>P_DFR-LUC</i> activity relative to the internal control (<i>REN</i> driven by 35S promoter). Error bars represent SE (n = 3). Asterisks represent Student's t-test significance between pairs indicated with brackets (*, P<0.05; **, P<0.01). (C) Transient transcriptional activity assays show that activation of <i>DFR</i> promoter by TT8/MYB75 is repressed by bHLH3 and bHLH17. The <i>P_DFR-LUC</i> reporter was cotransformed with the indicated constructs (10 µg for each construct). Error bars represent SE (n = 3). Asterisks represent Student's t-test significance (**, P<0.01). (D) The schematic diagrams show the constructs used in the transcriptional activity assays of (E). (E) Transient transcriptional activity assays show that activation of <i>TAT1</i> promoter by MYC2 is repressed by bHLH3 and bHLH17. The <i>P_TAT1-LUC</i> reporter was cotransformed with the indicated constructs (10 µg for each construct). Error bars represent SE (n = 3). Asterisks represent Student's t-test significance (*, P<0.05; **, P<0.01).