title: Repressing a repressor: gibberellin-induced rapid reduction of the RGA protein in Arabidopsis.
abstract: RGA (for repressor of ga1-3) and SPINDLY (SPY) are likely repressors of gibberellin (GA) signaling in Arabidopsis because the recessive rga and spy mutations partially suppressed the phenotype of the GA-deficient mutant ga1-3. We found that neither rga nor spy altered the GA levels in the wild-type or the ga1-3 background. However, expression of the GA biosynthetic gene GA4 was reduced 26% by the rga mutation, suggesting that partial derepression of the GA response pathway by rga resulted in the feedback inhibition of GA4 expression. The green fluorescent protein (GFP)-RGA fusion protein was localized to nuclei in transgenic Arabidopsis. This result supports the predicted function of RGA as a transcriptional regulator based on sequence analysis. Confocal microscopy and immunoblot analyses demonstrated that the levels of both the GFP-RGA fusion protein and endogenous RGA were reduced rapidly by GA treatment. Therefore, the GA signal appears to derepress the GA signaling pathway by degrading the repressor protein RGA. The effect of rga on GA4 gene expression and the effect of GA on RGA protein level allow us to identify part of the mechanism by which GA homeostasis is achieved.
authors.affiliation: Department of Biology, Box 91000, Duke University, Durham, NC 27708-1000, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Silverstone
authors.forename: H S
authors.initials: HS
authors.lastname: Jung
authors.forename: A
authors.initials: A
authors.lastname: Dill
authors.forename: H
authors.initials: H
authors.lastname: Kawaide
authors.forename: Y
authors.initials: Y
authors.lastname: Kamiya
authors.forename: T P
authors.initials: TP
authors.lastname: Sun
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins; D015152:Blotting, Northern; D002467:Cell Nucleus / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005809:Genes, Regulator; D005875:Gibberellins / Q000378:metabolism* / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D007553:Isotope Labeling; D008164:Luminescent Proteins / Q000235:genetics; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D010937:Plant Growth Regulators / Q000378:metabolism* / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D030821:Plants, Genetically Modified; D018749:RNA, Plant; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology*; D016415:Sequence Alignment; D015398:Signal Transduction; D013489:Suppression, Genetic; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D029681:Arabidopsis Proteins; D005875:Gibberellins; D008164:Luminescent Proteins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D018749:RNA, Plant; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; C101465:SPY protein, Arabidopsis; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D006899:Mixed Function Oxygenases; C108186:gibberellin 3beta-hydroxylase