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First published online October 21, 2005; 10.1104/pp.105.067645 Plant Physiology 139:1234-1243 (2005) © 2005 American Society of Plant Biologists Arabidopsis FHY1 Protein Stability Is Regulated by Light via Phytochrome A and 26S Proteasome1Peking-Yale Joint Center of Plant Molecular Genetics and Agrobiotechnology, College of Life Sciences, Peking University, Beijing 100871, China (Y.S., L.M., L.-J.Q., Z.C., X.W.D.); National Institute of Biological Sciences, Beijing 102206, China (Y.S., L.M.); Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520–8104 (Y.S., S.F., L.M., H.W., X.W.D.); and Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, New York 14853 (R.L., H.W.)
Phytochrome A (phyA) is the primary photoreceptor mediating responses to far-red light. Among the phyA downstream signaling components, Far-red Elongated Hypocotyl 1 (FHY1) is a genetically defined positive regulator of photomorphogenesis in far-red light. Both physiological and genomic characterization of the fhy1 mutants indicated a close functional relationship of FHY1 with phyA. Here, we showed that FHY1 is most abundant in young seedlings grown in darkness and is quickly down-regulated during further seedling development and by light exposure. By using light-insensitive 35S promoter-driven functional
1 This work was supported by the National Institutes of Health (grant no. GM47850 to X.W.D.), the National Science Foundation of China (strategic international cooperation project grant no. 30221120261), the National Institute of Biological Sciences at Beijing, and a Boyce Thompson Institute start-up fund (to H.W.). Y.S. was a Peking-Yale Center Monsanto fellow, and L.M. was a long-term fellow of the Human Frontier Science Program. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Xing Wang Deng (xingwang.deng{at}yale.edu). Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.067645. * Corresponding author; e-mail xingwang.deng{at}yale.edu; fax 203–432–5726. Received June 24, 2005; returned for revision August 29, 2005; accepted September 8, 2005. This article has been cited by other articles:
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-glucuronidase-FHY1 and green fluorescent protein-FHY1 fusion proteins, we showed that this down-regulation of FHY1 protein abundance by light is largely at posttranscriptional level and most evident in the nuclei. The light-triggered FHY1 protein reduction is primarily mediated through the 26S proteasome-dependent protein degradation. Further, phyA is directly involved in mediating the light-triggered down-regulation of FHY1, and the dark accumulation of FHY1 requires functional pleiotropic Constitutive Photomorphogenic/De-Etiolated/Fusca proteins. Our data indicate that phyA, the 26S proteasome, and the Constitutive Photomorphogenic/De-Etiolated/Fusca proteins are all involved in the light regulation of FHY1 protein abundance during Arabidopsis (Arabidopsis thaliana) seedling development. 
