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Targeted destabilization of HY5 during light-regulated development of Arabidopsis


Arabidopsis seedlings display contrasting developmental patterns depending on the ambient light. Seedlings grown in the light develop photomorphogenically, characterized by short hypocotyls and expanded green cotyledons. In contrast, seedlings grown in darkness become etiolated, with elongated hypocotyls and closed cotyledons on an apical hook. Light signals, perceived by multiple photoreceptors and transduced to downstream regulators, dictate the extent of photomorphogenic development in a quantitative manner. Two key downstream components, COP1 and HY5, act antagonistically in regulating seedling development1. HY5 is a bZIP transcription factor that binds directly to the promoters of light-inducible genes, promoting their expression and photomorphogenic development2,3. COP1 is a RING-finger protein with WD-40 repeats whose nuclear abundance is negatively regulated by light4,5. COP1 interacts directly with HY5 in the nucleus to regulate its activity negatively1. Here we show that the abundance of HY5 is directly correlated with the extent of photomorphogenic development, and that the COP1–HY5 interaction may specifically target HY5 for proteasome-mediated degradation in the nucleus.

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Figure 1: HY5 expression is regulated by light at both the mRNA and protein levels.
Figure 2: HY5 degradation is mediated by the proteasome pathway.
Figure 3: The pleiotropic COP/DET/FUS genes are essential for mediating light control of HY5 protein degradation but not its mRNA accumulation.
Figure 4: Several photoreceptors mediate the accumulation of HY5 under distinct wavelengths of light.
Figure 5: The light regulation of HY5 is dependent on the nuclear abundance of COP1 and its ability to interact with COP1.

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We thank R. Fry and H. Wang for reading and commenting on this manuscript, and A. Cashmore, C. Lin, P. Quail and G. Whitelam for providing Arabidopsis photoreceptor mutant strains. Our work was supported by grants from NIH (to X.W.D.), USDA (to N.W.) and the Human Frontiers Science Program Organization. X.W.D. is an NSF Presidential Faculty Fellow, M.T.O. is an NIH and Dept of Education predoctoral trainee and C.S.H. is a Human Frontier Science Program Organization postdoctoral fellow.

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Correspondence to Xing Wang Deng.

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Osterlund, M., Hardtke, C., Wei, N. et al. Targeted destabilization of HY5 during light-regulated development of Arabidopsis. Nature 405, 462–466 (2000).

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