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Plant Cell. 2015 Jan;27(1):189-201. doi: 10.1105/tpc.114.134775. Epub 2015 Jan 27.

Light-activated phytochrome A and B interact with members of the SPA family to promote photomorphogenesis in Arabidopsis by reorganizing the COP1/SPA complex.

Author information

1
Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany.
2
Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany Center for Plant Molecular Biology, University of Tübingen, 72076 Tübingen, Germany.
3
Center for Plant Molecular Biology, University of Tübingen, 72076 Tübingen, Germany Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany.
4
Department of Molecular Biosciences and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
5
Center for Plant Molecular Biology, University of Tübingen, 72076 Tübingen, Germany.
6
Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany andreas.hiltbrunner@biologie.uni-freiburg.de.

Abstract

Phytochromes function as red/far-red photoreceptors in plants and are essential for light-regulated growth and development. Photomorphogenesis, the developmental program in light, is the default program in seed plants. In dark-grown seedlings, photomorphogenic growth is suppressed by the action of the CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1)/SUPPRESSOR OF phyA-105 (SPA) complex, which targets positive regulators of photomorphogenic growth for degradation by the proteasome. Phytochromes inhibit the COP1/SPA complex, leading to the accumulation of transcription factors promoting photomorphogenesis; yet, the mechanism by which they inactivate COP1/SPA is still unknown. Here, we show that light-activated phytochrome A (phyA) and phytochrome B (phyB) interact with SPA1 and other SPA proteins. Fluorescence resonance energy transfer-fluorescence lifetime imaging microscopy analyses show that SPAs and phytochromes colocalize and interact in nuclear bodies. Furthermore, light-activated phyA and phyB disrupt the interaction between COP1 and SPAs, resulting in reorganization of the COP1/SPA complex in planta. The light-induced stabilization of HFR1, a photomorphogenic factor targeted for degradation by COP1/SPA, correlates temporally with the accumulation of phyA in the nucleus and localization of phyA to nuclear bodies. Overall, these data provide a molecular mechanism for the inactivation of the COP1/SPA complex by phyA- and phyB-mediated light perception.

PMID:
25627066
PMCID:
PMC4330587
DOI:
10.1105/tpc.114.134775
[Indexed for MEDLINE]
Free PMC Article

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