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Published on July 11, 2008; 10.1104/pp.108.123653

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Received May 29, 2008
Accepted June 18, 2008

Interactions of Two Transcriptional Repressors and Two Transcriptional Activators in Modulating Gibberellin Signaling in Aleurone Cells

Xiaolu Zou , Dawn Neuman , and Qingxi J. Shen *

School of Life Sciences, University of Nevada, Las Vegas, Nevada 89154

* Corresponding author; email: jeffery.shen{at}unlv.edu.

Gibberellins (GAs) regulate many aspects of plant development such as germination, growth, and flowering. The barley Amy32b {alpha}-amylase promoter contains at least five cis-acting elements that govern its GA-induced expression. Our previous studies indicates that a barley WRKY gene, HvWRKY38 and its rice ortholog, OsWRKY71, blocks GA induced expression of Amy32b-GUS. In this work, we investigated the functional and physical interactions of HvWRKY38 with another repressor and two activators in barley. HvWRKY38 blocks the inductive activities of SAD (a DOF protein) and HvGAMYB (a R2R3 MYB protein) when either of these proteins is present individually. However, SAD and HvGAMYB together overcome the inhibitory effect of HvWRKY38. Yet combination of HvWRKY38 and BPBF (another DOF protein) almost diminishes the synergistic effect of SAD and HvGAMYB transcriptional activators. Electrophoretic mobility shift assays indicate that HvWRKY38 blocks GA-induced expression of Amy32b by interfering with the binding of HvGAMYB to the cis-acting elements in the {alpha}-amylase promoter. The physical interaction of HvWRKY38 and BPBF repressors is demonstrated via Bimolecular Fluorescence Complementation (BiFC) assays. These data suggest that the expression of Amy32b is modulated by protein complexes that contain either activators (e.g. HvGAMYB and SAD) or repressors (e.g. HvWRKY38 and BPBF). The relative amounts of the repressor or activator complexes binding to the Amy32b promoter regulate its expression level in barley aleurone cells.






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