title: Factorial combinations of protein interactions generate a multiplicity of florigen activation complexes in wheat and barley.
abstract: 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.
authors.affiliation: Department Plant Sciences, University of California, Davis, CA, USA.|Howard Hughes Medical Institute, Chevy Chase, MD, USA.
authors.forename: Chengxia
authors.initials: C
authors.lastname: Li
authors.affiliation: Department Plant Sciences, University of California, Davis, CA, USA.
authors.forename: Huiqiong
authors.initials: H
authors.lastname: Lin
authors.affiliation: Department Plant Sciences, University of California, Davis, CA, USA.|Howard Hughes Medical Institute, Chevy Chase, MD, USA.|Gordon and Betty Moore Foundation, Palo Alto, CA, USA.
authors.forename: Jorge
authors.initials: J
authors.lastname: Dubcovsky
mesh_terms: D060405:Florigen / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D001467:Hordeum / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D011485:Protein Binding; D014908:Triticum / Q000378:metabolism*
chemical_list: D060405:Florigen; D010940:Plant Proteins
keywords: 14-3-3; FDL; FLOWERING LOCUS T; Hordeum vulgare; Triticum aestivum; VRN1; florigen activation complex; flowering