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Plant Cell Advance Online Publication
Published on October 26, 2007; 10.1105/tpc.107.053017

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Received May 31, 2007
Returned for revision August 28, 2007
Accepted October 4, 2007

Arabidopsis Cryptochrome 2 Completes Its Posttranslational Life Cycle in the Nucleus

Xuhong Yu 1, John Klejnot 1, Xiaoying Zhao 2, Dror Shalitin 1, Maskit Maymon 1, Hongyun Yang 1, Janet Lee 1, Xuanming Liu 2, Javier Lopez 1, and Chentao Lin 1*

1 Department of Molecular, Cell, and Developmental Biology, University of California, Los Angeles, California 90095
2 Bioenergy and Biomaterial Research Center, Hunan University, Changsha 410082, China

* To whom correspondence should be addressed. E-mail: clin{at}mcdb.ucla.edu.

CRY2 is a blue light receptor regulating light inhibition of hypocotyl elongation and photoperiodic flowering in Arabidopsis thaliana. The CRY2 protein is found primarily in the nucleus, and it is known to undergo blue light–dependent phosphorylation and degradation. However, the subcellular location where CRY2 exerts its function or undergoes blue light–dependent phosphorylation and degradation remains unclear. In this study, we analyzed the function and regulation of conditionally nuclear-localized CRY2. Our results show that CRY2 mediates blue light inhibition of hypocotyl elongation and photoperiodic promotion of floral initiation in the nucleus. Consistent with this result and a hypothesis that blue light–dependent phosphorylation is associated with CRY2 function, we demonstrate that CRY2 undergoes blue light–dependent phosphorylation in the nucleus. CRY2 phosphorylation is required for blue light–dependent CRY2 degradation, but only a limited quantity of CRY2 is phosphorylated at any given moment in seedlings exposed to blue light, which explains why continuous blue light illumination is required for CRY2 degradation. Finally, we showed that CRY2 is ubiquitinated in response to blue light and that ubiquitinated CRY2 is degraded by the 26S proteasome in the nucleus. These findings demonstrate that a photoreceptor can complete its posttranslational life cycle (from protein modification, to function, to degradation) inside the nucleus.






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