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Proc Natl Acad Sci U S A. 2012 Aug 14;109(33):13446-51. doi: 10.1073/pnas.1119992109. Epub 2012 Jul 30.

Molecular mechanism for the interaction between gibberellin and brassinosteroid signaling pathways in Arabidopsis.

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1
Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain.

Abstract

Plant development is modulated by the convergence of multiple environmental and endogenous signals, and the mechanisms that allow the integration of different signaling pathways is currently being unveiled. A paradigmatic case is the concurrence of brassinosteroid (BR) and gibberellin (GA) signaling in the control of cell expansion during photomorphogenesis, which is supported by physiological observations in several plants but for which no molecular mechanism has been proposed. In this work, we show that the integration of these two signaling pathways occurs through the physical interaction between the DELLA protein GAI, which is a major negative regulator of the GA pathway, and BRASSINAZOLE RESISTANT1 (BZR1), a transcription factor that broadly regulates gene expression in response to BRs. We provide biochemical evidence, both in vitro and in vivo, indicating that GAI inactivates the transcriptional regulatory activity of BZR1 upon their interaction by inhibiting the ability of BZR1 to bind to target promoters. The physiological relevance of this interaction was confirmed by the observation that the dominant gai-1 allele interferes with BR-regulated gene expression, whereas the bzr1-1D allele displays enhanced resistance to DELLA accumulation during hypocotyl elongation. Because DELLA proteins mediate the response to multiple environmental signals, our results provide an initial molecular framework for the integration with BRs of additional pathways that control plant development.

PMID:
22847438
PMCID:
PMC3421204
DOI:
10.1073/pnas.1119992109
[Indexed for MEDLINE]
Free PMC Article
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