Poster: Photomorphogenesis
Abs #
510: Functional interactions of COP1 and SPA1 in repressing photomorphogenic development of Arabidopsis.
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Presenter: |
Saijo, Yusuke , yusuke.saijo@yale.edu | Authors | Saijo, Yusuke (A) Wang, Haiyang (A) (B) Sullivan, James A (A) Ma, Ligeng (A) Rubio, Vicente (A) Shen, Yunping (A) Deng, Xing Wang (A) | | Affiliations: |
(A): Dept of Molecular, Cellular and Developmental Biology, Yale University
(B): Boyce Thompson Institute for Plant Research, Cornell University
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| Web Site: | http://www.yale.edu/denglab/ | |
Arabidopsis COP1 is a negative regulator of photomorphogenesis. The WD40 domain of COP1 is responsible for the direct interaction with photomorphogenesis-promoting factors such as HY5 (a bZIP transcription factor), and subsequent proteasome-mediated degradation. SPA1, a negative regulator of phytochrome A (PHYA) signaling, has a WD40 domain highly homologous to that of COP1 and physically interacts with COP1 in vitro, suggesting the possibility that these two proteins work together in targeted destabilization of the substrate proteins. Here we show that SPA1 also interacts with HY5 in yeast two-hybrid assays and that HY5 protein accumulates to high levels in spa1-3 mutant seedlings under the continuous far-red light (cFR). In addition, genetic studies indicate a closer functional relationship than simply additive one between COP1 and SPA1. The spa1-3 mutation enhances the weak cop1-6 mutant phenotype under cFR as well as dark conditions, where no obvious phenotype is observed in dark-grown spa1-3 mutant plants. The genomic expression profiles obtained by microarray analyses focusing on the far-red light regulated genes are also consistent with these genetic observations. Using the epitope-tagged SPA1 transgenic plants, we found that the SPA1 fusion protein interacts with COP1 in vivo. Gel filtration analyses of plant protein extracts show that COP1 exists as a part of an approximately 700 kDa protein complex. Taken together, our data supports the hypothesis that SPA1 acts in concert with COP1 in repressing the PHYA-mediated photomorphogenic responses, by helping COP1 to capture the substrates and/or modulating the proposed ubiquitin E3 ligase activity of COP1.
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