title: Distinct roles of FKF1, Gigantea, and Zeitlupe proteins in the regulation of Constans stability in Arabidopsis photoperiodic flowering.
abstract: Many plants measure changes in day length to synchronize their flowering time with appropriate seasons for maximum reproductive success. In Arabidopsis, the day-length-dependent regulation of Constans (CO) protein stability is crucial to induce flowering locus T (FT) expression for flowering in long days. The flavin-binding, KELCH repeat, F-box1 (FKF1) protein binds to CO protein specifically in the long-day afternoon and stabilizes it, although the mechanism remains unknown. Here we demonstrated that the FKF1-interacting proteins Gigantea (GI) and Zeitlupe (ZTL) are involved in CO stability regulation. First, our immunoprecipitation-mass spectrometry analysis of FKF1 revealed that FKF1 forms an S-phase kinase-associated protein 1 (Skp1)/Cullin(CUL)/F-box complex through interactions with Arabidopsis Skp1-like 1 (ASK1), ASK2, and CUL1 proteins and mainly interacts with GI protein in vivo. GI interacts with CO directly and indirectly through FKF1. Unexpectedly, the gi mutation increases the CO protein levels in the morning in long days. This gi-dependent destabilization of CO protein was cancelled by the fkf1 mutation. These results suggest that there are other factors likely influenced by both gi and fkf1 mutations that also control CO stability. We found that ZTL, which interacts with GI and FKF1, may be one such factor. ZTL also interacts with CO in vivo. The CO protein profile in the ztl mutant resembles that in the gi mutant, indicating that ZTL activity also may be changed in the gi mutant. Our findings suggest the presence of balanced regulation among FKF1, GI, and ZTL on CO stability regulation for the precise control of flowering time.
authors.affiliation: Departments of Biology and Department of Life Sciences, Ajou University, Suwon 443-749, Korea; and.
authors.forename: Young Hun
authors.initials: YH
authors.lastname: Song
authors.affiliation: Departments of Biology and.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Estrada
authors.affiliation: Genome Sciences, University of Washington, Seattle, WA 98195;
authors.forename: Richard S
authors.initials: RS
authors.lastname: Johnson
authors.affiliation: Departments of Biology and.
authors.forename: Somi K
authors.initials: SK
authors.lastname: Kim
authors.affiliation: Plant Molecular Biology and Biotechnology Research Center (Post-BK21 Program), Gyeongsang National University, Jinju 660-701, Korea.
authors.forename: Sang Yeol
authors.initials: SY
authors.lastname: Lee
authors.affiliation: Genome Sciences, University of Washington, Seattle, WA 98195;
authors.forename: Michael J
authors.initials: MJ
authors.lastname: MacCoss
authors.affiliation: Departments of Biology and takato@u.washington.edu.
authors.forename: Takato
authors.initials: T
authors.lastname: Imaizumi
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology*; D035264:Flowers / Q000235:genetics / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D008027:Light; D009154:Mutation; D017440:Photoperiod; D011401:Promoter Regions, Genetic; D012621:Seasons; D015398:Signal Transduction; D014157:Transcription Factors / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; C092776:CONSTANS protein, Arabidopsis; D004268:DNA-Binding Proteins; C410504:FKF1 protein, Arabidopsis; C121183:GI protein, Arabidopsis; D014157:Transcription Factors; C410503:ZTL protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases
keywords: E3 ubiquitin ligase; blue-light photoreceptor; photoperiodic flowering; protein degradation