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Gating of the rapid shade-avoidance response by the circadian clock in plants


The phytochromes are a family of plant photoreceptor proteins that control several adaptive developmental strategies1,2. For example, the phytochromes perceive far-red light (wavelengths between 700 and 800 nm) reflected or scattered from the leaves of nearby vegetation. This provides an early warning of potential shading, and triggers a series of ‘shade-avoidance’ responses, such as a rapid increase in elongation3, by which the plant attempts to overgrow its neighbours3. Other, less immediate, responses include accelerated flowering and early production of seeds. However, little is known about the molecular events that connect light perception with increased growth in shade avoidance. Here we show that the circadian clock gates this rapid shade-avoidance response. It is most apparent around dusk and is accompanied by altered expression of several genes. One of these rapidly responsive genes encodes a basic helix–loop–helix protein, PIL1, previously shown to interact with the clock protein TOC1 (ref. 4). Furthermore PIL1 and TOC1 are both required for the accelerated growth associated with the shade-avoidance response.

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Figure 1: Quantitative PCR of PIL1 transcript in response to low R/FR in La-er.
Figure 2: Quantitative PCR of changes in PIL1 transcript abundance in phy mutants in response to low R/FR (grey bars), compared with control (black bars).
Figure 3: Circadian gating of low-R/FR-induced hypocotyl elongation in wild-type La-er (diamonds) and mutant (squares) seedlings.
Figure 4: Hypocotyl elongation responses in pil1, PIL1ox and toc1-2 seedlings.


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We thank E. Halligan, D. Lowes and J. Lunec for assistance with the Affymetrix microarrays, T. Ingles for assistance in creating transgenic lines, and A. Millar for providing toc1 alleles. This work was supported by grants from the Biotechnology and Biological Research Council, UK.

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Correspondence to Garry C. Whitelam.

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Salter, M., Franklin, K. & Whitelam, G. Gating of the rapid shade-avoidance response by the circadian clock in plants. Nature 426, 680–683 (2003).

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