Identification of the conserved serine/threonine residues important for gibberellin‐sensitivity of Arabidopsis RGL2 protein
Open Access
- 6 September 2005
- journal article
- Published by Wiley in The Plant Journal
- Vol. 44 (1) , 88-99
- https://doi.org/10.1111/j.1365-313x.2005.02512.x
Abstract
Summary: The DELLA proteins GAI, RGA, RGL1 and RGL2 in Arabidopsis are plant growth repressors, repressing diverse developmental processes. Studies have shown that gibberellin (GA) attenuates the repressive function of DELLA proteins by triggering their degradation via the proteasome pathway. However, it is not known if GA‐induced protein degradation is the only pathway for regulating the bioactivity of DELLA proteins. We show here that tobacco BY2 cells represent a suitable system for studying GA signaling. RGL2 exists in a phosphorylated form in BY2 cells. RGL2 undergoes GA‐induced degradation, and this process is blocked by proteasome inhibitors and serine/threonine phosphatase inhibitors; however, serine/threonine kinase inhibitors had no detectable effect, suggesting that dephosphorylation of serine/threonine is probably a prerequisite for degradation of RGL2 via the proteasome pathway. Site‐directed substitution of all 17 conserved serine and threonine residues showed that six mutants (RGL2S441D, RGL2S542D, RGL2T271E, RGL2T319E, RGL2T411E and RGL2T535E) mimicking the status of constitutive phosphorylation are resistant to GA‐induced degradation. This suggests that these sites are potential phosphorylation sites. A functional assay based on the expression of GA 20‐oxidase revealed that RGL2T271E is probably a null mutant, RGL2S441D, RGL2S542D, RGL2T319E and RGL2T411E only retained about 4–17% of the activity of the wild type RGL2, whereas RGL2T535E retained about 66% of the activity of the wild type RGL2. However, expression of GA 20‐oxidase in BY2 cells expressing these mutant proteins is still responsive to GA, suggesting that the stabilization of RGL2 protein is not the only pathway for regulating its bioactivity.Keywords
This publication has 44 references indexed in Scilit:
- Mitotic Cyclins Stimulate the Activity of c-Myb-like Factors for Transactivation of G2/M Phase-specific Genes in TobaccoJournal of Biological Chemistry, 2004
- Mutation of a CK2 phosphorylation site in cdc25C impairs importin α/β binding and results in cytoplasmic retentionOncogene, 2004
- Phosphorylation of Bim-EL by Erk1/2 on serine 69 promotes its degradation via the proteasome pathway and regulates its proapoptotic functionOncogene, 2003
- A role for the ubiquitin–26S-proteasome pathway in gibberellin signalingTrends in Plant Science, 2003
- The ArabidopsisSLEEPY1Gene Encodes a Putative F-Box Subunit of an SCF E3 Ubiquitin Ligase[W]Plant Cell, 2003
- Relieving DELLA RestraintScience, 2003
- Gibberellin-Mediated Proteasome-Dependent Degradation of the Barley DELLA Protein SLN1 RepressorPlant Cell, 2002
- Expression of Arabidopsis GAI in Transgenic Rice Represses Multiple Gibberellin ResponsesPlant Cell, 2001
- Gibberellins Signal Nuclear Import of PHOR1, a Photoperiod-Responsive Protein with Homology to Drosophila armadilloCell, 2001
- Feedback Regulation of GA5 Expression and Metabolic Engineering of Gibberellin Levels in ArabidopsisPlant Cell, 1999