title: The role of SPY and its TPR domain in the regulation of gibberellin action throughout the life cycle of Petunia hybrida plants.
abstract: SPY acts as a negative regulator of gibberellin (GA) action in Arabidopsis, but its mode of action and regulation are still unknown. SPY over-expression in transgenic petunia plants affected various GA-regulated processes, including seed germination, shoot elongation, flower initiation, flower development and the expression of a GA-induced gene, GIP. A similar phenotype was obtained when wild-type petunia plants were treated with the GA-biosynthesis inhibitor, paclobutrazol. The N-terminus of SPY contains tetratricopeptide repeats (TPR). TPR motifs participate in protein-protein interactions, suggesting that SPY is part of a multiprotein complex. To test this hypothesis, we over-expressed the SPY's TPR region without the catalytic domain in transgenic petunia and generated a dominant-negative SPY mutant. The transgenic seeds were able to germinate on paclobutrazol, suggesting an enhanced GA signal. We cloned the petunia SPY homologue, PhSPY, and showed that its mRNA level is not affected by GA or ABA. The results of this study support the role of SPY as a negative regulator of GA action, suggest that the TPR domain is required for the interaction with other proteins to form an active complex and indicate that different plants use similar mechanisms to transduce the GA signal.
authors.affiliation: The Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, PO Box 12, Rehovot 76100, Israel.
authors.forename: A
authors.initials: A
authors.lastname: Izhaki
authors.forename: S M
authors.initials: SM
authors.lastname: Swain
authors.forename: T S
authors.initials: TS
authors.lastname: Tseng
authors.forename: A
authors.initials: A
authors.lastname: Borochov
authors.forename: N E
authors.initials: NE
authors.lastname: Olszewski
authors.forename: D
authors.initials: D
authors.lastname: Weiss
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins; D017124:Conserved Sequence; D005875:Gibberellins / Q000378:metabolism*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000254:growth & development; D020449:Repetitive Sequences, Amino Acid; D012097:Repressor Proteins; D015398:Signal Transduction / Q000502:physiology; D019657:Solanaceae / Q000254:growth & development*
chemical_list: D029681:Arabidopsis Proteins; D005875:Gibberellins; D010940:Plant Proteins; D012097:Repressor Proteins; C101465:SPY protein, Arabidopsis