Minisymposium 4: Signaling

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Abs # M0402: 14-3-3 proteins bind to Brassinazole Resistant 1 (BZR1) to regulate its activity

Presenter:	Gampala, Satyalinga Srinivas       Contact Presenter
Authors	Gampala, Satyalinga Srinivas  (A)   He, Jun-Xian  (A)   Bai, Mingyi  (B)   Guan, Shenheng  (C)   Sun, Ying  (A)   Gendron, Joshua M. (A)   Chen, Jasmine J. (A)   Peck, Scott  (D)   Burlingame, Alma L. (C)   Chong, Kang  (B)   Wang, Zhi-Yong  (A)
Affiliations:	(A): Department of Plant Biology, Carnegie Institution (B): Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, The Chinese Academy of Sciences (C): Department of Pharmaceutical Chemistry, University of California-San Francisco (D): Department of Biochemistry, University of Missouri-Columbia

Brassinosteroids (BR) play important roles in regulation of plant growth and development. The BR signaling pathway in Arabidopsis is well-defined and includes cell-surface receptor kinases BRI1 and BAK1, a GSK3 kinase BIN2, and the nuclear-localized transcription factors BZR1 and BZR2/BES1. We have previously shown that BZR1 is a transcription factor with dual roles in BR homeostasis and growth responses, and that BZR1 is negatively regulated through phosphorylation by BIN2. How BZR1 activity is regulated at the molecular level and the proteins involved in the process remain largely unknown. In the current study, several 14-3-3 proteins were identified in both Arabidopsis and rice as BZR1-interacting proteins using yeast two-hybrid screens. In vivo interaction between BZR1 and 14-3-3 was detected using Bi-Molecular Fluorescence Complementation, and in vitro overlay assays demonstrated that 14-3-3 proteins specifically interact with phosphorylated BZR1. BZR1 peptides containing the phosphorylated 14-3-3 binding site were detected by mass spectrometry in plant nuclear extracts as well as in vitro after BIN2 phosphorylation. Deletion of the 14-3-3 binding site altered the subcellular localization pattern of BZR1, and expression of this mutated BZR1 in transgenic plants caused bzr1-1D phenotypes, including curled and twisted leaves, kinks in floral stems, and long hypocotyls on brassinazole. These results suggest that the activity of BZR1 is inhibited by phosphorylation-dependent binding to 14-3-3 proteins and disruption of such binding by BR-induced BZR1 dephosphorylation would lead to increased BZR1 activity, which appears to be a mechanism conserved in Arabidopsis and rice.