DE1, a 12-Base Pair cis-Regulatory Element Sufficient to Confer Dark-inducible and Light Down-regulated Expression to a Minimal Promoter in Pea

We found a cis-regulatory element of 12 base pairs (bp) (GGATTTTACAGT) capable of conferring light responsiveness to a minimal promoter, CaMV 35S46, in pea. The 12-bp sequence is located in the 5' upstream region of the light down-regulated gene pra2, which encodes a small GTPase belonging to the YPT/rab family. Here we examined gain-of-function analyses using synthetic promoter-luciferase constructs in a transient assay and found that the 12-bp element alone was sufficient to confer dark induction, as well as light down- regulation on the minimal promoter. We named this dark inducible element DE1. Effects of various light conditions on the reporter gene activity showed that DE1 received signals from phytochrome A, phytochrome B, and blue light photoreceptors. Using phytochrome-deficient mutants, we showed that the pra2 protein level in seedlings was also regulated by these photoreceptors. The changes in the immunoblotting pattern of the pra2 protein in these mutants were correlated with the changes in epicotyl elongation. Results from transient assays using these mutants showed that the DE1 received signals from phytochromes A and B, demonstrating that this element is indeed a light- responsive element. To our knowledge, this is the first cis-element that by itself confers light responsiveness to a minimal promoter.