BZS1, a B-box protein, promotes photomorphogenesis downstream of both brassinosteroid and light signaling pathways.
ABSTRACT Photomorphogenesis is controlled by multiple signaling pathways, including the light and brassinosteroid (BR) pathways. BR signaling activates the BZR1 transcription factor, which is required for suppressing photomorphogenesis in the dark. We identified a suppressor of the BR hypersensitive mutant bzr1-1D and named it bzr1-1D suppressor1-Dominant (bzs1-D). The bzs1-D mutation was caused by overexpression of a B-box zinc finger protein BZS1, which is transcriptionally repressed by BZR1. Overexpression of BZS1 causes de-etiolation in the dark, short hypocotyls in the light, reduced sensitivity to BR treatment, and repression of many BR-activated genes. Knockdown of BZS1 by co-suppression partly suppressed the short hypocotyl phenotypes of BR-deficient or insensitive mutants. These results support that BZS1 is a negative regulator of BR response. BZS1 overexpressors are hypersensitive to different wavelengths of light and loss of function of BZS1 reduces plant sensitivity to light and partly suppresses the constitutive photomorphogenesis 1 (cop1) mutant in the dark, suggesting a positive role in light response. BZS1 protein accumulates at an increased level after light treatment of dark-grown BZS1-OX plants and in the cop1 mutants, and BZS1 interacts with COP1 in vitro, suggesting that light regulates BZS1 through COP1-mediated ubiquitination and proteasomal degradation. These results demonstrate that BZS1 mediates the crosstalk between BR and light pathways.
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ABSTRACT: Many hormonal and environmental signals regulate common cellular and developmental processes in plants. While the molecular pathways that transduce these signals have each been studied in detail, how these pathways are wired into regulatory networks to provide the coordinated responses has remained an outstanding question. Recent studies of the brassinosteroid signaling network have revealed extensive signal integration through direct interactions between components of different signaling pathways. In particular, a circuit of interacting transcription regulators integrates many signaling pathways to enable coordinated and coherent regulation of seedling morphogenesis by hormonal and environmental signals. The recent studies support an emerging theme that complex networks of highly integrated signaling pathways underlie the high levels of developmental plasticity and environmental adaptability of plants.Current Opinion in Plant Biology 10/2014; 21:147–153. · 9.39 Impact Factor
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ABSTRACT: Brassinosteroids are plant steroid hormones that regulate plant organs and chloroplast development. The detailed molecular mechanism for plant development by BR signaling is yet to be revealed, and many points regarding the relationship between BR signaling and chloroplast development remain unknown. We identify here the dominant mutant Brz-insensitive-pale green3-1D (bpg3-1D) from the Arabidopsis FOX lines that show reduced sensitivity to the chlorophyll accumulation promoted by the BR biosynthesis inhibitor, Brassinazole (Brz), in the light. BPG3 encodes a novel chloroplast protein that is evolutionally conserved in bacteria, algae, and higher plants. The expression of BPG3 was induced by light and Brz. The inhibition of electron transport in photosystem II of the chloroplasts was detected in bpg3-1D. These results suggest that BPG3 played an important role in regulating photosynthesis in the chloroplast under BR signaling.Bioscience Biotechnology and Biochemistry 03/2014; 78(3):420-9. · 1.27 Impact Factor
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ABSTRACT: Light is a pivotal environmental stimulus that promotes plant photomorphogenesis. Substantial progress has been achieved in defining the central repressors of photomorphogenesis, the CONSTITUTIVE PHOTOMORPHOGENIC/DE-ETIOLATED/FUSCA (COP/DET/FUS) loci, in the past 20 years. COP/DET/FUS proteins are well-conserved, and regulate a variety of biological processes in plants and animals. The fact that these proteins contribute to the repression of plant photomorphogenesis by regulating the ubiquitin-proteasome-dependent pathway has been well established. Recently, molecular insight has been gained into the functional diversity of COP/DET/FUS. Here, we review the current research on the roles of COP/DET/FUS, with a focus on the functional conversion of COP1 in photomorphogenesis.Current Opinion in Plant Biology. 01/2014; 21:96–103.