title: Cross talk between gibberellin and cytokinin: the Arabidopsis GA response inhibitor SPINDLY plays a positive role in cytokinin signaling.
abstract: SPINDLY (SPY) is a negative regulator of gibberellin (GA) responses; however, spy mutants exhibit various phenotypic alterations not found in GA-treated plants. Assaying for additional roles for SPY revealed that spy mutants are resistant to exogenously applied cytokinin. GA also repressed the effects of cytokinin, suggesting that there is cross talk between the two hormone-response pathways, which may involve SPY function. Two spy alleles showing severe (spy-4) and mild (spy-3) GA-associated phenotypes exhibited similar resistance to cytokinin, suggesting that SPY enhances cytokinin responses and inhibits GA signaling through distinct mechanisms. GA and spy repressed numerous cytokinin responses, from seedling development to senescence, indicating that cross talk occurs early in the cytokinin-signaling pathway. Because GA3 and spy-4 inhibited induction of the cytokinin primary-response gene, type-A Arabidopsis response regulator 5, SPY may interact with and modify elements from the phosphorelay cascade of the cytokinin signal transduction pathway. Cytokinin, on the other hand, had no effect on GA biosynthesis or responses. Our results demonstrate that SPY acts as both a repressor of GA responses and a positive regulator of cytokinin signaling. Hence, SPY may play a central role in the regulation of GA/cytokinin cross talk during plant development.
authors.affiliation: Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel.
authors.forename: Yaarit
authors.initials: Y
authors.lastname: Greenboim-Wainberg
authors.forename: Inbar
authors.initials: I
authors.lastname: Maymon
authors.forename: Roy
authors.initials: R
authors.lastname: Borochov
authors.forename: John
authors.initials: J
authors.lastname: Alvarez
authors.forename: Neil
authors.initials: N
authors.lastname: Olszewski
authors.forename: Naomi
authors.initials: N
authors.lastname: Ori
authors.forename: Yuval
authors.initials: Y
authors.lastname: Eshed
authors.forename: David
authors.initials: D
authors.lastname: Weiss
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003583:Cytokinins / Q000378:metabolism* / Q000494:pharmacology; D004351:Drug Resistance / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D005875:Gibberellins / Q000378:metabolism* / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D036226:Seedlings / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D003583:Cytokinins; D005875:Gibberellins; D012097:Repressor Proteins; C101465:SPY protein, Arabidopsis