PIF5 Directly Binds to the CCA1 Promoter and Represses Its Expression.
(A) Yeast one-hybrid assay showing that PIF3 and PIF5 directly bind to the CCA1 promoter. PIF3 and PIF5, but not PIF1 and PIF4, activated the AbAr reporter gene driven by the wild-type CCA1 promoter but not the AbAr reporter gene driven by the CCA1 promoter with a mutated G-box element. Empty vector expressing the activation domain (AD) alone was used as the negative control.
(B) EMSA showing that GST-PIF3 and GST-PIF5 bHLH (DNA binding domain) specifically bind to the biotin-labeled CCA1p-G-box (right) probe. The arrowheads indicate GST-PIF3 and GST-PIF5 bHLH proteins.
(C) Transient expression assay showing that PIF5 represses CCA1 expression in N. benthamiana leaf cells (**, P < 0.05, Student’s t test). Values are means ± sd (n = 3 technical replicates). Three independent biological replicates showed similar results.