title: The Elucidation of the Interactome of 16 Arabidopsis bZIP Factors Reveals Three Independent Functional Networks.
abstract: The function of the bZIP transcription factors is strictly dependent on their ability to dimerize. Heterodimerization has proven to be highly specific and is postulated to operate as a combinatorial mechanism allowing the generation of a large variety of dimers with unique qualities by specifically combining a small set of monomers; an assumption that has not yet been tested systematically. Here, the interaction pattern and the transactivation properties of 16 Arabidopsis thaliana bZIPs are examined in transiently transformed Arabidopsis protoplasts to deliver a perspective on the relationship between bZIP dimerization and function. An interaction matrix of bZIPs belonging to the C, G, H, and S1 bZIP groups was resolved by Bimolecular Fluorescent Complementation (BiFC) coupled to quantitative flow cytometric analysis, while an extensive GUS reporter gene assay was carried out to determine the effect of different bZIP pairs on the expression of four different known bZIP-targeted promoters. Statistical data treatment and complementary bioinformatic analysis were performed to substantiate the biological findings. According to these results, the 16 bZIPs interact in three isolated networks, within which their members dimerize non-specifically and exhibit a significant level of functional redundancy. A coherent explanation for these results is supported by in silico analysis of differences in the length, structure and composition of their leucine zippers and appears to explain their dimerization specificity and dynamics observed in vivo quite well. A model in which the bZIP networks act as functional units is proposed.
authors.affiliation: Center for Plant Molecular Biology (ZMBP), University of Tübingen, Tübingen, Germany.
authors.forename: Carles Marco
authors.initials: CM
authors.lastname: Llorca
authors.affiliation: Center for Plant Molecular Biology (ZMBP), University of Tübingen, Tübingen, Germany.
authors.forename: Kenneth Wayne
authors.initials: KW
authors.lastname: Berendzen
authors.affiliation: Biostatistics Unit, Institute of Crop Science, University of Hohenheim, Stuttgart, Germany.
authors.forename: Waqas Ahmed
authors.initials: WA
authors.lastname: Malik
authors.affiliation: Center for Plant Molecular Biology (ZMBP), University of Tübingen, Tübingen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mahn
authors.affiliation: Biostatistics Unit, Institute of Crop Science, University of Hohenheim, Stuttgart, Germany.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Piepho
authors.affiliation: Center for Plant Molecular Biology (ZMBP), University of Tübingen, Tübingen, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Zentgraf
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050976:Basic-Leucine Zipper Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D053263:Gene Regulatory Networks / Q000502:physiology*; D016350:Leucine Zippers; D056004:Molecular Dynamics Simulation
chemical_list: D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors