A Rice WRKY Gene Encodes a Transcriptional Repressor of the Gibberellin Signaling Pathway in Aleurone Cells

Abstract

The molecular mechanism by which GA regulates plant growth and development has been a subject of active research. Analyses of the rice (Oryza sativa) genomic sequences identified 77 WRKY genes, among which OsWRKY71 is highly expressed in aleurone cells. Transient expression of OsWRKY71 by particle bombardment specifically represses GA-induced Amy32b α-amylase promoter but not abscisic acid-induced HVA22 or HVA1 promoter activity in aleurone cells. Moreover, OsWRKY71 blocks the activation of the Amy32b promoter by the GA-inducible transcriptional activator OsGAMYB. Consistent with its role as a transcriptional repressor, OsWRKY71 is localized to nuclei of aleurone cells and binds specifically to functionally defined TGAC-containing W boxes of the Amy32b promoter in vitro. Mutation of the two W boxes prevents the binding of OsWRKY71 to the mutated promoter, and releases the suppression of the OsGAMYB-activated Amy32b expression by OsWRKY71, suggesting that OsWRKY71 blocks GA signaling by functionally interfering with OsGAMYB. Exogenous GA treatment decreases the steady-state mRNA level of OsWRKY71 and destabilizes the GFP:OsWRKY71 fusion protein. These findings suggest that OsWRKY71 encodes a transcriptional repressor of GA signaling in aleurone cells.

WRKY transcription factors: from DNA binding towards biological function

“…In roots, numerous Arabidopsis WRKY genes are expressed in a specifically localised domain, hinting that they have a specialised role in cell maturation [42 ]. A role in hormone signaling was observed for the rice WRKY factor OsWRKY71, which acts as a transcriptional repressor of gibberellin-responsive genes [43]. In pepper, CaWRKY1 expression is strongly upregulated in red fruit and may play an important role in fruit maturation (CH Harn, pers.…”

Global Analysis of DELLA Direct Targets in Early Gibberellin Signaling inArabidopsis

“…aleurone cells, act as transcriptional repressors of GA signaling that interfere with GAMYB and block a-amylase gene expression (Zhang et al, 2004;Xie et al, 2006). DELLA-induced WRKY27 may play a similar role in regulating GA signaling in Arabidopsis.…”

Characterization of an Elicitor-Induced Rice WRKY Gene,OsWRKY71

“…14) Recently, we reported that OsWRKY53 functions as a transcriptional activator in the defense responses in rice. 15) With regard to OsWRKY71, when we started this study, its involvement in the regulation ofamylase gene expression in aleurone cells had been reported, 16) but the role of OsWRKY71 in defense responses was almost unknown. In this study, we found that OsWRKY71 has features characteristic of a transcriptional repressor, and that overexpression of OsWR-KY71 in rice causes up-regulation of several elicitorinduced defense-related genes.…”