ABSTRACT
G-BOX BINDING FACTOR 1 (GBF1) influences light-regulated seedling development in Arabidopsis, and inhibits CATALASE 2 (CAT2) expression during senescence. CAT2 functions as a scavenger of hydrogen peroxide. The role of GBF1 in the defense response is not known. We report here that GBF1 positively influences the defense against virulent and avirulent strains of Pseudomonas syringae. The gbf1 mutants are susceptible, whereas GBF1 over-expresser transgenic plants are resistant to bacterial pathogens. GBF1 negatively regulates pathogen-induced CAT2 expression and thereby positively regulates the hypersensitive response. In addition to CAT2 promoter, GBF1 binds to the G-box-like element present in the intron of PHYTOALEXIN DEFICIENT 4 (PAD4). This association of GBF1 with PAD4 intron is enhanced upon pathogenesis. GBF1 positively regulates PAD4 transcription in an intron-dependent manner. GBF1-mediated positive regulation of PAD4 expression is also evident in gbf1 mutant and GBF1 over-expression lines. Similar to pad4 mutants, pathogen-induced camalexin and salicylic acid (SA) accumulation, and expression of SA-inducible PATHOGENESIS RELATED1 (PR1) gene are compromised in the gbf1 mutant. Exogenous application of SA rescues the loss-of-defense phenotypes of gbf1 mutant. Thus, altogether, our results demonstrate that GBF1 is an important component of the plant defense response that functions upstream of SA accumulation and, by oppositely regulating CAT2 and PAD4, promotes disease resistance in Arabidopsis.
Subject(s)
Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Arabidopsis/genetics , Carboxylic Ester Hydrolases/genetics , Disease Resistance , Plant Diseases/immunology , Pseudomonas syringae/immunology , Transcription Factors/metabolism , Arabidopsis/immunology , Arabidopsis/microbiology , Carboxylic Ester Hydrolases/metabolism , Gene Expression Regulation, Plant , Indoles/metabolism , Introns/genetics , Mutation , Plant Diseases/microbiology , Plants, Genetically Modified , Salicylic Acid/metabolism , Thiazoles/metabolism , Transcription Factors/geneticsABSTRACT
A defining feature of plant leaves is their flattened shape. This shape depends on an antagonism between the genes that specify adaxial (top) and abaxial (bottom) tissue identity; however, the molecular nature of this antagonism remains poorly understood. Class III homeodomain leucine zipper (HD-ZIP) transcription factors are key mediators in the regulation of adaxial-abaxial patterning. Their expression is restricted adaxially during early development by the abaxially expressed microRNA (MIR)165/166, yet the mechanism that restricts MIR165/166 expression to abaxial leaf tissues remains unknown. Here, we show that class III and class II HD-ZIP proteins act together to repress MIR165/166 via a conserved cis-element in their promoters. Organ morphology and tissue patterning in plants, therefore, depend on a bidirectional repressive circuit involving a set of miRNAs and its targets.
Subject(s)
Homeodomain Proteins/genetics , Leucine Zippers/genetics , MicroRNAs/genetics , Plant Development/genetics , Plant Leaves/genetics , Arabidopsis/genetics , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Biomarkers , Conserved Sequence , Gene Expression Regulation, Plant , Homeodomain Proteins/chemistry , Homeodomain Proteins/metabolism , Models, Biological , Protein Binding , Quantitative Trait, Heritable , Response ElementsSubject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/metabolism , Basic-Leucine Zipper Transcription Factors/metabolism , Carrier Proteins/metabolism , DNA, Plant/metabolism , Nuclear Proteins/metabolism , Transcription Factors/metabolism , Arabidopsis/genetics , Arabidopsis Proteins/genetics , Basic-Leucine Zipper Transcription Factors/genetics , Carrier Proteins/genetics , DNA, Plant/genetics , DNA-Binding Proteins , Dimerization , Genome, Plant , Nuclear Proteins/genetics , Protein Binding , Transcription Factors/geneticsABSTRACT
One set of genes encoding diverse groups of transcription factors that interact with the Z-box (ATACGTGT; a potential Z-DNA forming sequence) is called ZBFs (Z-box Binding Factors). ZBFs include ZBF1, ZBF2, and ZBF3, which encode ZBF1/MYC2 (bHLH), ZBF2/GBF1 (bZIP), and ZBF3/CAM7 (Calmodulin) proteins, respectively. With several recent reports, it is becoming increasingly evident that ZBFs play crucial roles in Arabidopsis seedling photomorphogenesis. ZBFs integrate signals from various wavelengths of light to coordinate the regulation of transcriptional networks that affect multiple facets of plant growth and development. The function of each ZBF is qualitatively and quantitatively distinct. The zbf mutants display pleiotropic effects including altered hypocotyl elongation, cotyledon expansion, lateral root development, and flowering time. In this inaugural review, we discuss the identification, molecular functions, and interacting partners of ZBFs in light-mediated Arabidopsis seedling development.
Subject(s)
Arabidopsis Proteins/physiology , Arabidopsis/growth & development , Transcription Factors/physiology , Anthocyanins/metabolism , Arabidopsis/metabolism , Chlorophyll/metabolism , Etiolation , Flowers/growth & development , Light , Plant Roots/growth & development , Protein Stability , Signal Transduction , Transcription, GeneticABSTRACT
The bZIP proteins, GBF1, HY5 and HYH, play important regulatory roles in Arabidopsis seedling development. Whereas GBF1 plays a dual regulatory role, HY5 and HYH act as positive regulators of photomorphogenesis. The molecular and functional relations of GBF1 with HY5 and HYH in photomorphogenesis have recently been demonstrated. However, the possible interaction of bZIP domain of each of these proteins remains to be investigated. In this study, our results suggest that bZIP domains of HY5 and HYH are able to interact with the bZIP domain of GBF1. Taken together with the earlier study, (9) these results suggest that the N-terminal domain of GBF1 has an inhibitory effect on its interaction with HY5 and HYH.
Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/metabolism , Basic-Leucine Zipper Transcription Factors/metabolism , Carrier Proteins/metabolism , Gene Expression Regulation, Plant , Nuclear Proteins/metabolism , Seedlings/metabolism , Transcription Factors/metabolism , Arabidopsis/genetics , Arabidopsis/growth & development , DNA-Binding Proteins , Light , Seedlings/growth & developmentABSTRACT
Arabidopsis bZIP transcription factor, GBF1, acts as a differential regulator of cryptochrome-mediated blue light signaling. Whereas the bZIP proteins, HY5 (elongated hypocotyl 5) and HYH (HY5 homologue), are degraded by COP1-mediated proteasomal pathways, GBF1 is degraded by a proteasomal pathway independent of COP1. In this study, we have investigated the functional interrelations of GBF1 with HY5 and HYH in Arabidopsis seedling development. The genetic studies using double and triple mutants reveal that GBF1 largely acts antagonistically with HY5 and HYH in Arabidopsis seedling development. Further, GBF1 and HY5 play more important roles than HYH in blue light-mediated photomorphogenic growth. This study reveals that GBF1 is able to form a G-box-binding heterodimer with HY5 but not with HYH. The in vitro and in vivo studies demonstrate that GBF1 co-localizes with HY5 or HYH in the nucleus and physically interacts with both of the proteins. The protein-protein interaction studies further reveal that the bZIP domain of GBF1 is essential and sufficient for the interaction with HY5 or HYH. Taken together, these data demonstrate the functional interrelations of GBF1 with HY5 and HYH in Arabidopsis seedling development.
Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/growth & development , Basic-Leucine Zipper Transcription Factors/metabolism , Carrier Proteins/metabolism , Hypocotyl/growth & development , Nuclear Proteins/metabolism , Transcription Factors/metabolism , Arabidopsis/genetics , Arabidopsis/metabolism , Arabidopsis Proteins/chemistry , Arabidopsis Proteins/genetics , Basic-Leucine Zipper Transcription Factors/genetics , Carrier Proteins/genetics , DNA-Binding Proteins , Epistasis, Genetic , Gene Expression Regulation, Plant/radiation effects , Hypocotyl/genetics , Hypocotyl/metabolism , Light , Mutation , Nuclear Proteins/genetics , Onions/cytology , Onions/metabolism , Phenotype , Plants, Genetically Modified/growth & development , Plants, Genetically Modified/metabolism , Promoter Regions, Genetic , Protein Binding , Protein Interaction Domains and Motifs , Protein Multimerization , Protein Structure, Quaternary , Protein Transport , Transcription Factors/chemistry , Transcription Factors/geneticsABSTRACT
Arabidopsis GBF1/ZBF2 is a bZIP transcription factor that plays dual but opposite regulatory roles in cryptochrome-mediated blue light signaling. Here, we show the genetic and molecular interrelation of GBF1 with two well characterized negative regulators of light signaling, COP1 and SPA1, in photomorphogenic growth and light-regulated gene expression. Our results further reveal that GBF1 protein is less abundant in the dark-grown seedlings and is degraded by a proteasome-mediated pathway independent of COP1 and SPA1. Furthermore, COP1 physically interacts with GBF1 and is required for the optimum accumulation of GBF1 protein in light-grown seedlings. Taken together, this study provides a mechanistic view of concerted function of three important regulators in Arabidopsis seedling development.
