title: Distinct roles of GIGANTEA in promoting flowering and regulating circadian rhythms in Arabidopsis.
abstract: The circadian clock acts as the timekeeping mechanism in photoperiodism. In Arabidopsis thaliana, a circadian clock-controlled flowering pathway comprising the genes GIGANTEA (GI), CONSTANS (CO), and FLOWERING LOCUS T (FT) promotes flowering specifically under long days. Within this pathway, GI regulates circadian rhythms and flowering and acts earlier in the hierarchy than CO and FT, suggesting that GI might regulate flowering indirectly by affecting the control of circadian rhythms. We studied the relationship between the roles of GI in flowering and the circadian clock using late elongated hypocotyl circadian clock associated1 double mutants, which are impaired in circadian clock function, plants overexpressing GI (35S:GI), and gi mutants. These experiments demonstrated that GI acts between the circadian oscillator and CO to promote flowering by increasing CO and FT mRNA abundance. In addition, circadian rhythms in expression of genes that do not control flowering are altered in 35S:GI and gi mutant plants under continuous light and continuous darkness, and the phase of expression of these genes is changed under diurnal cycles. Therefore, GI plays a general role in controlling circadian rhythms, and this is different from its effect on the amplitude of expression of CO and FT. Functional GI:green fluorescent protein is localized to the nucleus in transgenic Arabidopsis plants, supporting the idea that GI regulates flowering in the nucleus. We propose that the effect of GI on flowering is not an indirect effect of its role in circadian clock regulation, but rather that GI also acts in the nucleus to more directly promote the expression of flowering-time genes.
authors: Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
authors: Tsuyoshi
authors: T
authors: Mizoguchi
authors: Louisa
authors: L
authors: Wright
authors: Sumire
authors: S
authors: Fujiwara
authors: Frédéric
authors: F
authors: Cremer
authors: Karen
authors: K
authors: Lee
authors: Hitoshi
authors: H
authors: Onouchi
authors: Aidyn
authors: A
authors: Mouradov
authors: Sarah
authors: S
authors: Fowler
authors: Hiroshi
authors: H
authors: Kamada
authors: Joanna
authors: J
authors: Putterill
authors: George
authors: G
authors: Coupland
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics*; D002940:Circadian Rhythm / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D003624:Darkness; D035264:Flowers / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D018546:Hypocotyl / Q000235:genetics; D008027:Light; D026161:MADS Domain Proteins / Q000235:genetics*; D008954:Models, Biological; D017440:Photoperiod; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D029681:Arabidopsis Proteins; C092776:CONSTANS protein, Arabidopsis; D004268:DNA-Binding Proteins; C418902:At5g10140 protein, Arabidopsis; C121183:GI protein, Arabidopsis; D026161:MADS Domain Proteins; D014157:Transcription Factors