Li Chengxia, Lin Huiqiong, Dubcovsky Jorge
Department Plant Sciences, University of California, Davis, CA, USA.
Howard Hughes Medical Institute, Chevy Chase, MD, USA.
Plant J. 2015 Oct;84(1):70-82. doi: 10.1111/tpj.12960. Epub 2015 Sep 6.
The FLOWERING LOCUS T (FT) protein is a central component of a mobile flowering signal (florigen) that is transported from leaves to the shoot apical meristem (SAM). Two FT monomers and two DNA-binding bZIP transcription factors interact with a dimeric 14-3-3 protein bridge to form a hexameric protein complex. This complex, designated as the 'florigen activation complex' (FAC), plays a critical role in flowering. The wheat homologue of FT, designated FT1 (= VRN3), activates expression of VRN1 in the leaves and the SAM, promoting flowering under inductive long days. In this study, we show that FT1, other FT-like proteins, and different FD-like proteins, can interact with multiple wheat and barley 14-3-3 proteins. We also identify the critical amino acid residues in FT1 and FD-like proteins required for their interactions, and demonstrate that 14-3-3 proteins are necessary bridges to mediate the FT1-TaFDL2 interaction. Using in vivo bimolecular fluorescent complementation (BiFC) assays, we demonstrate that the interaction between FT1 and 14-3-3 occurs in the cytoplasm, and that this complex is then translocated to the nucleus, where it interacts with TaFDL2 to form a FAC. We also demonstrate that a FAC including FT1, TaFDL2 and Ta14-3-3C can bind to the VRN1 promoter in vitro. Finally, we show that relative transcript levels of FD-like and 14-3-3 genes vary among tissues and developmental stages. Since FD-like proteins determine the DNA specificity of the FACs, variation in FD-like gene expression can result in spatial and temporal modulation of the effects of mobile FT-like signals.
成花素基因座T（FT）蛋白是一种可移动的成花信号（成花素）的核心成分，该信号从叶片运输至茎尖分生组织（SAM）。两个FT单体和两个DNA结合bZIP转录因子与一个二聚体14-3-3蛋白桥相互作用，形成一个六聚体蛋白复合物。这个复合物被称为“成花素激活复合物”（FAC），在开花过程中起关键作用。FT的小麦同源物，命名为FT1（=VRN3），激活叶片和SAM中VRN1的表达，在诱导性长日照条件下促进开花。在本研究中，我们表明FT1、其他FT样蛋白以及不同的FD样蛋白能够与多种小麦和大麦14-3-3蛋白相互作用。我们还确定了FT1和FD样蛋白相互作用所需的关键氨基酸残基，并证明14-3-3蛋白是介导FT1-TaFDL2相互作用的必要桥梁。通过体内双分子荧光互补（BiFC）分析，我们证明FT1与14-3-3之间的相互作用发生在细胞质中，然后这个复合物转移到细胞核，在那里它与TaFDL2相互作用形成FAC。我们还证明包含FT1、TaFDL2和Ta14-3-3C的FAC能够在体外与VRN1启动子结合。最后，我们表明FD样和14-3-3基因的相对转录水平在不同组织和发育阶段有所不同。由于FD样蛋白决定了FAC的DNA特异性，FD样基因表达的变化会导致可移动FT样信号效应的时空调节。
