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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
Plant Physiology
Vol. 139, No. 3 (Nov., 2005), pp. 1234-1243
Stable URL: http://www.jstor.org/stable/4281952
Page Count: 10
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Arabidopsis FHY1 Protein Stability Is Regulated by Light via Phytochrome a and 26s Proteasome
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Abstract

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 β-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.

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