Arabidopsis F-box protein SLEEPY1 targets gibberellin signaling repressors for gibberellin-induced degradation

• Published in: The Plant cell 2004-06, Vol.16 (6), p.1392-1405
• Main Authors: Dill, A, Thomas, S.G, Hu, J, Steber, C.M, Sun, T.P
• Format: Article
• Language: English
• Subjects: Alkyl and Aryl Transferases; Alleles; Amino Acid Sequence; Amino acids; Arabidopsis - cytology; Arabidopsis - drug effects; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; binding proteins; Binding Sites; Cell Nucleus - metabolism; DNA; F box proteins; F-Box Proteins - chemistry; F-Box Proteins - genetics; F-Box Proteins - metabolism; Genes, Plant - genetics; Genetic mutation; Gibberellins; Gibberellins - pharmacology; Molecular Sequence Data; mutants; Mutation; Mutation - genetics; Onions - cytology; Onions - metabolism; phenotype; Phenotypes; Plant cells; Plant Proteins; Plants; Protein Binding; protein degradation; Protein Processing, Post-Translational - drug effects; Protein Structure, Tertiary; Proteins; proteolysis; regulatory proteins; signal transduction; Signal Transduction - drug effects; Transcription Factors - chemistry; Transcription Factors - genetics; Transcription Factors - metabolism; Two-Hybrid System Techniques; Yeasts
• ISSN: 1040-4651; 1532-298X; 1532-298X
• DOI: 10.1105/tpc.020958

The nuclear DELLA proteins are highly conserved repressors of hormone gibberellin (GA) signaling in plants. In Arabidopsis thaliana, GA derepresses its signaling pathway by inducing proteolysis of the DELLA protein REPRESSOR OF ga1-3 (RGA). SLEEPY1 (SLY1) encodes an F-box-containing protein, and the loss-of-function sly1 mutant has a GA-insensitive dwarf phenotype and accumulates a high level of RGA. These findings suggested that SLY1 recruits RGA to the SCF(SLY1) E3 ligase complex for ubiquitination and subsequent degradation by the 26S proteasome. In this report, we provide new insight into the molecular mechanism of how SLY1 interacts with the DELLA proteins for controlling GA response. By yeast two-hybrid and in vitro pull-down assays, we demonstrated that SLY1 interacts directly with RGA and GA INSENSITIVE (GAI, a closely related DELLA protein) via their C-terminal GRAS domain. The rga and gai null mutations additively suppressed the recessive sly1 mutant phenotype, further supporting the model that SCFSLY1 targets both RGA and GAI for degradation. The N-terminal DELLA domain of RGA previously was shown to be essential for GA-induced degradation. However, we found that this DELLA domain is not required for protein¡protein interaction with SLY1 in yeast (Saccharomyces cerevisiae), suggesting that its role is in a GA-triggered conformational change of the DELLA proteins. We also identified a novel gain-of-function sly1-d mutation that increased GA signaling by reducing the levels of the DELLA protein in plants. This effect of sly1-d appears to be caused by an enhanced interaction between sly1-d and the DELLA proteins.