title: GeBP and GeBP-like proteins are noncanonical leucine-zipper transcription factors that regulate cytokinin response in Arabidopsis.
abstract: Understanding the role of transcription factors (TFs) is essential in reconstructing developmental regulatory networks. The plant-specific GeBP TF family of Arabidopsis thaliana (Arabidopsis) comprises 21 members, all of unknown function. A subset of four members, the founding member GeBP and GeBP-like proteins (GPL) 1, 2, and 3, shares a conserved C-terminal domain. Here we report that GeBP/GPL genes represent a newly defined class of leucine-zipper (Leu-zipper) TFs and that they play a redundant role in cytokinin hormone pathway regulation. Specifically, we demonstrate using yeast, in vitro, and split-yellow fluorescent protein in planta assays that GeBP/GPL proteins form homo- and heterodimers through a noncanonical Leu-zipper motif located in the C-terminal domain. A triple loss-of-function mutant of the three most closely related genes gebp gpl1 gpl2 shows a reduced sensitivity to exogenous cytokinins in a subset of cytokinin responses such as senescence and growth, whereas root inhibition is not affected. We find that transcript levels of type-A cytokinin response genes, which are involved in the negative feedback regulation of cytokinin signaling, are higher in the triple mutant. Using a GPL version that acts as a constitutive transcriptional activator, we show that the regulation of Arabidopsis response regulators (ARRs) is mediated by at least one additional, as yet unknown, repressor acting genetically downstream in the GeBP/GPL pathway. Our results indicate that GeBP/GPL genes encode a new class of unconventional Leu-zipper TF proteins and suggest that their role in the cytokinin pathway is to antagonize the negative feedback regulation on ARR genes to trigger the cytokinin response.
authors.affiliation: Laboratoire Plastes et Différenciation Cellulaire, CNRS, Université Joseph Fourier, Grenoble, France.
authors.forename: Florian
authors.initials: F
authors.lastname: Chevalier
authors.forename: Daniel
authors.initials: D
authors.lastname: Perazza
authors.forename: Frédéric
authors.initials: F
authors.lastname: Laporte
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Le Hénanff
authors.forename: Patricia
authors.initials: P
authors.lastname: Hornitschek
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Bonneville
authors.forename: Michel
authors.initials: M
authors.lastname: Herzog
authors.forename: Gilles
authors.initials: G
authors.lastname: Vachon
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003583:Cytokinins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D025461:Feedback, Physiological / Q000502:physiology; D018506:Gene Expression Regulation, Plant; D016350:Leucine Zippers; D005810:Multigene Family; D009154:Mutation; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
chemical_list: C117138:ARR1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D003583:Cytokinins; D004268:DNA-Binding Proteins; C000629467:STKR1 protein, Arabidopsis; D014157:Transcription Factors