Laubinger Sascha, Marchal Virginie, Le Gourrierec José, Wenkel Stephan, Adrian Jessika, Jang Seonghoe, Kulajta Carmen, Braun Helen, Coupland George, Hoecker Ute
Department of Plant Developmental and Molecular Biology, Geb. 26.03.02, University of Düsseldorf, D-40225 Düsseldorf, Germany.
Development. 2006 Aug;133(16):3213-22. doi: 10.1242/dev.02481. Epub 2006 Jul 19.
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.
拟南芥的四成员SPA蛋白家族与E3泛素连接酶COP1协同作用，抑制暗中生长幼苗的光形态建成。在此，我们进一步证明SPA蛋白对于光周期开花至关重要。SPA1的突变在短日照（SD）而非长日照（LD）条件下导致不依赖phyA的早花，并且这种表型因SPA3和SPA4功能的额外丧失而增强。这些spa1 spa3 spa4三突变体在LD和SD条件下同时开花，表明SPA基因家族对于在非诱导性SD条件下抑制开花至关重要。在四个SPA基因中，SPA1对于正常的光周期开花是必需且充分的。SD条件下生长的spa突变体早花与FT转录水平的强烈增加相关，而CO转录水平未改变。上位性分析表明，spa1突变体中的早花和FT诱导完全依赖于CO。与此发现一致，SPA蛋白在体外和体内与CO发生物理相互作用，表明SPA蛋白调节CO蛋白功能。结构域定位表明，SPA1-CO相互作用需要CO的CCT结构域，但不依赖于CO的B-box型锌指结构。我们进一步表明，spa1 spa3 spa4突变体表现出CO蛋白水平的强烈增加，这不是由CO基因表达的变化引起的。综上所述，我们的结果表明，SPA蛋白通过控制成花诱导因子CO的稳定性来调节光周期开花。
