Received June 24, 2005
Returned for revision August 29, 2005
Accepted September 8, 2005
Arabidopsis FHY1 Protein Stability Is Regulated by Light via Phytochrome A and 26S Proteasome
Yunping Shen , Suhua Feng , Ligeng Ma , Rongcheng Lin , Li-Jia Qu , Zhangliang Chen , Haiyang Wang , and Xing Wang Deng *
Peking-Yale Joint Center of Plant Molecular Genetics and Agrobiotechnology, College of Life Sciences, Peking University, Beijing 100871, China; National Institute of Biological Sciences, Beijing 102206, China; Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8104
Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8104
Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, New York 14853
Peking-Yale Joint Center of Plant Molecular Genetics and Agrobiotechnology, College of Life Sciences, Peking University, Beijing 100871, China
Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8104; Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, New York 14853
Peking-Yale Joint Center of Plant Molecular Genetics and Agrobiotechnology, College of Life Sciences, Peking University, Beijing 100871, China; Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8104
* Corresponding author; email: xingwang.deng{at}yale.edu.
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
-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.