Functional interaction of phytochrome B and cryptochrome 2

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Abstract

Light is a crucial environmental signal that controls many photomorphogenic and circadian responses in plants1. Perception and transduction of light is achieved by at least two principal groups of photoreceptors, phytochromes and cryptochromes2,3. Phytochromes are red/far-red light-absorbing receptors encoded by a gene family of five members (phyA to phyE)2,4 in Arabidopsis. Cryptochrome 1 (cry1), cryptochrome 2 (cry2) and phototropin are the blue/ultraviolet-A light receptors that have been characterized in Arabidopsis5. Previous studies showed that modulation of many physiological responses in plants is achieved by genetic interactions between different photoreceptors6; however, little is known about the nature of these interactions and their roles in the signal transduction pathway. Here we show the genetic interaction that occurs between the Arabidopsis photoreceptors phyB and cry2 in the control of flowering time, hypocotyl elongation and circadian period by the clock. PhyB interacts directly with cry2 as observed in co-immunoprecipitation experiments with transgenic Arabidopsis plants overexpressing cry2. Using fluorescent resonance energy transfer microscopy, we show that phyB and cry2 interact in nuclear speckles that are formed in a light-dependent fashion.

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Figure 1: Physiological and biochemical evidence for interaction between cry2 and phyB.
Figure 2: Effects of light on cry2–RFP subcellular distribution and colocalization with phyB–GFP in BY-2 cells.
Figure 3: FRET analysis of phyB–GFP and cry2–RFP interaction.
Figure 4: FRET microscopy by acceptor photobleaching.

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Acknowledgements

We thank S. L. Harmer, T. F. Schultz and M. J. Yanovsky for critical comments of the manuscript. We are grateful to C. Lin for providing cry2 cDNA, the cry2 overexpression line and cry2 antibody. We also thank A. Nagatani for the phyB–GFP construct and anti-phyB antibody. We thank G. Patterson and D. Piston for GFP spectra data, and Clontech for DsRFP spectra data. We are grateful to D. Millar and T. K. Nomanbhoy for helpful discussion on FRET analysis. Research support came from the NIH. P.M. was supported by a Novartis Agricultural Discovery Institute and P.F.D. was supported by an European Molecular Biology Organization long-term fellowship and the NSF. S.P. was supported by TSRI graduate program.

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Correspondence to Steve A. Kay.

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