First published online September 14, 2007; 10.1105/tpc.107.053728
The Plant Cell 19:2749-2762 (2007)
© 2007 American Society of Plant Biologists
OPEN ACCESS ARTICLE
Nucleocytoplasmic Shuttling of BZR1 Mediated by Phosphorylation Is Essential in Arabidopsis Brassinosteroid Signaling[W],[OA]
Hojin Ryua,1,
Kangmin Kima,1,
Hyunwoo Choa,
Joonghyuk Parka,
Sunghwa Choeb and
Ildoo Hwanga,2
a Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
b Department of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea
2 Address correspondence to ihwang{at}postech.ac.kr.
Phytohormone brassinosteroids (BRs) play critical roles in plant growth and development. BR acts by modulating the phosphorylation status of two key transcriptional factors, BRI1 EMS SUPPRESSOR1 and BRASSINAZOLE RESISTANT1 (BZR1), through the action of BRASSINOSTEROID INSENSITIVE1/BRI1 ASSOCIATED RECEPTOR KINASE1 receptors and a GSK3 kinase, BRASSINOSTEROID INSENSITIVE2 (BIN2). It is still unknown how the perception of BR at the plasma membrane connects to the expression of BR target genes in the nucleus. We show here that BZR1 functions as a nucleocytoplasmic shuttling protein and GSK3-like kinases induce the nuclear export of BZR1 by modulating BZR1 interaction with the 14-3-3 proteins. BR-activated phosphatase mediates rapid nuclear localization of BZR1. Besides the phosphorylation domain for 14-3-3 binding, another phosphorylation domain in BZR1 is required for the BIN2-induced nuclear export of BZR1. Mutations of putative phosphorylation sites in two distinct domains enhance the nuclear retention of BZR1 and BR responses in transgenic plants. We propose that the spatial redistribution of BZR1 is critical for proper BR signaling in plant growth and development.
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