title: Integration of Phytochrome and Cryptochrome Signals Determines Plant Growth during Competition for Light.
abstract: Plants in dense vegetation perceive their neighbors primarily through changes in light quality. Initially, the ratio between red (R) and far-red (FR) light decreases due to reflection of FR by plant tissue well before shading occurs. Perception of low R:FR by the phytochrome photoreceptors induces the shade avoidance response [1], of which accelerated elongation growth of leaf-bearing organs is an important feature. Low R:FR-induced phytochrome inactivation leads to the accumulation and activation of the transcription factors PHYTOCHROME-INTERACTING FACTORs (PIFs) 4, 5, and 7 and subsequent expression of their growth-mediating targets [2, 3]. When true shading occurs, transmitted light is especially depleted in red and blue (B) wavelengths, due to absorption by chlorophyll [4]. Although the reduction of blue wavelengths alone does not occur in nature, long-term exposure to low B light induces a shade avoidance-like response that is dependent on the cryptochrome photoreceptors and the transcription factors PIF4 and PIF5 [5-7]. We show in Arabidopsis thaliana that low B in combination with low R:FR enhances petiole elongation similar to vegetation shade, providing functional context for a low B response in plant competition. Low B potentiates the low R:FR response through PIF4, PIF5, and PIF7, and it involves increased PIF5 abundance and transcriptional changes. Low B attenuates a low R:FR-induced negative feedback loop through reduced gene expression of negative regulators and reduced HFR1 levels. The enhanced response to combined phytochrome and cryptochrome inactivation shows how multiple light cues can be integrated to fine-tune the plant's response to a changing environment.
authors.affiliation: Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, the Netherlands; Centre for Integrative Genomics, Lausanne University, Génopode Building, 1015 Lausanne, Switzerland.
authors.forename: Mieke
authors.initials: M
authors.lastname: de Wit
authors.affiliation: Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, the Netherlands.
authors.forename: Diederik H
authors.initials: DH
authors.lastname: Keuskamp
authors.affiliation: Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, the Netherlands.
authors.forename: Franca J
authors.initials: FJ
authors.lastname: Bongers
authors.affiliation: Centre for Integrative Genomics, Lausanne University, Génopode Building, 1015 Lausanne, Switzerland.
authors.forename: Patricia
authors.initials: P
authors.lastname: Hornitschek
authors.affiliation: Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, the Netherlands.
authors.forename: Charlotte M M
authors.initials: CMM
authors.lastname: Gommers
authors.affiliation: Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, the Netherlands.
authors.forename: Emilie
authors.initials: E
authors.lastname: Reinen
authors.affiliation: Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, the Netherlands.
authors.forename: Carmen
authors.initials: C
authors.lastname: Martínez-Cerón
authors.affiliation: Centre for Integrative Genomics, Lausanne University, Génopode Building, 1015 Lausanne, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Fankhauser
authors.affiliation: Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, the Netherlands. Electronic address: r.pierik@uu.nl.
authors.forename: Ronald
authors.initials: R
authors.lastname: Pierik
mesh_terms: D017360:Arabidopsis / Q000254:growth & development* / Q000528:radiation effects*; D029681:Arabidopsis Proteins; D056931:Cryptochromes / Q000502:physiology*; D018524:Phototropism; D010834:Phytochrome / Q000502:physiology*; D036226:Seedlings / Q000254:growth & development; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D056931:Cryptochromes; D010834:Phytochrome
keywords: COP1; HFR1; PHYTOCHROME INTERACTING FACTOR; blue light; cryptochrome; phytochrome; plant competition; red:far-red ratio; shade avoidance; signal integration