title: Arabidopsis SPA proteins regulate photoperiodic flowering and interact with the floral inducer CONSTANS to regulate its stability.
abstract: The four-member SPA protein family of Arabidopsis acts in concert with the E3 ubiquitin ligase COP1 to suppress photomorphogenesis in dark-grown seedlings. Here, we demonstrate that SPA proteins are, moreover, essential for photoperiodic flowering. Mutations in SPA1 cause phyA-independent early flowering under short day (SD) but not long day (LD) conditions, and this phenotype is enhanced by additional loss of SPA3 and SPA4 function. These spa1 spa3 spa4 triple mutants flower at the same time in LD and SD, indicating that the SPA gene family is essential for the inhibition of flowering under non-inductive SD. Among the four SPA genes, SPA1 is necessary and sufficient for normal photoperiodic flowering. Early flowering of SD-grown spa mutant correlates with strongly increased FT transcript levels, whereas CO transcript levels are not altered. Epistasis analysis demonstrates that both early flowering and FT induction in spa1 mutants is fully dependent on CO. Consistent with this finding, SPA proteins interact physically with CO in vitro and in vivo, suggesting that SPA proteins regulate CO protein function. Domain mapping shows that the SPA1-CO interaction requires the CCT-domain of CO, but is independent of the B-box type Zn fingers of CO. We further show that spa1 spa3 spa4 mutants exhibit strongly increased CO protein levels, which are not caused by a change in CO gene expression. Taken together, our results suggest, that SPA proteins regulate photoperiodic flowering by controlling the stability of the floral inducer CO.
authors.affiliation: Department of Plant Developmental and Molecular Biology, Geb. 26.03.02, University of Düsseldorf, D-40225 Düsseldorf, Germany.
authors.forename: Sascha
authors.initials: S
authors.lastname: Laubinger
authors.forename: Virginie
authors.initials: V
authors.lastname: Marchal
authors.forename: José
authors.initials: J
authors.lastname: Le Gourrierec
authors.forename: José
authors.initials: J
authors.lastname: Gentilhomme
authors.forename: Stephan
authors.initials: S
authors.lastname: Wenkel
authors.forename: Jessika
authors.initials: J
authors.lastname: Adrian
authors.forename: Seonghoe
authors.initials: S
authors.lastname: Jang
authors.forename: Carmen
authors.initials: C
authors.lastname: Kulajta
authors.forename: Helen
authors.initials: H
authors.lastname: Braun
authors.forename: George
authors.initials: G
authors.lastname: Coupland
authors.forename: Ute
authors.initials: U
authors.lastname: Hoecker
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D035264:Flowers / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D017343:Genes, Plant; D009154:Mutation; D017440:Photoperiod; D051942:Phytochrome A / Q000378:metabolism; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; C092776:CONSTANS protein, Arabidopsis; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C497973:PHYA protein, Arabidopsis; D051942:Phytochrome A; C118571:SPA1 protein, Arabidopsis; D014157:Transcription Factors