title: The clock protein CCA1 and the bZIP transcription factor HY5 physically interact to regulate gene expression in Arabidopsis.
abstract: The circadian clock regulates the expression of an array of Arabidopsis genes such as those encoding the LIGHT-HARVESTING CHLOROPHYLL A/B (Lhcb) proteins. We have previously studied the promoters of two of these Arabidopsis genes--Lhcb1*1 and Lhcb1*3--and identified a sequence that binds the clock protein CIRCADIAN CLOCK ASSOCIATED 1 (CCA1). This sequence, designated CCA1-binding site (CBS), is necessary for phytochrome and circadian responsiveness of these genes. In close proximity to this sequence, there exists a G-box core element that has been shown to bind the bZIP transcription factor HY5 in other light-regulated plant promoters. In the present study, we examined the importance of the interaction of transcription factors binding the CBS and the G-box core element in the control of normal circadian rhythmic expression of Lhcb genes. Our results show that HY5 is able to specifically bind the G-box element in the Lhcb promoters and that CCA1 can alter the binding activity of HY5. We further show that CCA1 and HY5 can physically interact and that they can act synergistically on transcription in a yeast reporter gene assay. An absence of HY5 leads to a shorter period of Lhcb1*1 circadian expression but does not affect the circadian expression of CATALASE3 (CAT3), whose promoter lacks a G-box element. Our results suggest that interaction of the HY5 and CCA1 proteins on Lhcb promoters is necessary for normal circadian expression of the Lhcb genes.
authors.affiliation: Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, CA 90095-1606, USA.
authors.forename: Christos
authors.initials: C
authors.lastname: Andronis
authors.forename: Simon
authors.initials: S
authors.lastname: Barak
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Knowles
authors.forename: Shoji
authors.initials: S
authors.lastname: Sugano
authors.forename: Elaine M
authors.initials: EM
authors.lastname: Tobin
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000187:drug effects / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D015152:Blotting, Northern; D055864:Droughts; D005030:Ethylenes / Q000494:pharmacology; D035264:Flowers / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000528:radiation effects; D018546:Hypocotyl / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D008027:Light; D009154:Mutation; D010641:Phenotype; D010750:Phosphoproteins / Q000502:physiology; D010937:Plant Growth Regulators / Q000494:pharmacology; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000528:radiation effects; D011523:Protoplasts / Q000187:drug effects / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D014157:Transcription Factors / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; C114425:CCA1 protein, Arabidopsis; D005030:Ethylenes; D010750:Phosphoproteins; D010937:Plant Growth Regulators; D014157:Transcription Factors; C036216:ethylene