Abstract
Higher plants possess multiple members of the phytochrome family of red, far-red light sensors to modulate plant growth and development according to competition from neighbors. The phytochrome family is composed of the light-labile phyA and several light-stable members (phyB-phyE in Arabidopsis). phyA accumulates to high levels in etiolated seedlings and is essential for young seedling establishment under a dense canopy. In photosynthetically active seedlings high levels of phyA counteract the shade avoidance response. phyA levels are maintained low in light-grown plants by a combination of light-dependent repression of PHYA transcription and light-induced proteasome-mediated degradation of the activated photoreceptor. Light-activated phyA is transported from the cytoplasm where it resides in darkness to the nucleus where it is needed for most phytochrome-induced responses. Here we show that phyA is degraded by a proteasome-dependent mechanism both in the cytoplasm and the nucleus. However, phyA degradation is significantly slower in the cytoplasm than in the nucleus. In the nucleus phyA is degraded in a proteasome-dependent mechanism even in its inactive Pr (red light absorbing) form, preventing the accumulation of high levels of nuclear phyA in darkness. Thus, light-induced degradation of phyA is in part controlled by a light-regulated import into the nucleus where the turnover is faster. Although most phyA responses require nuclear phyA it might be useful to maintain phyA in the cytoplasm in its inactive form to allow accumulation of high levels of the light sensor in etiolated seedlings.
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Acknowledgments
We thank Karin Schumacher and Akira Nagatani for providing antibodies against DET3 and phyA respectively, Sérerine Lorrain for critically reading the manuscript and Matthias Zeidler for his kind gift of the fhy1fhl double mutant. Microscopy was performed in the Cellular Imaging Facility platform (CIF) from the University of Lausanne and we wish to thank Arnaud Paradis for his help. Funding was provided by the University of Lausanne and a grant from the Swiss National Science Foundation to C. F. (Grant n° 3100A0-112638).
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Debrieux, D., Fankhauser, C. Light-induced degradation of phyA is promoted by transfer of the photoreceptor into the nucleus. Plant Mol Biol 73, 687–695 (2010). https://doi.org/10.1007/s11103-010-9649-9
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DOI: https://doi.org/10.1007/s11103-010-9649-9