Identification of Primary Target Genes of Phytochrome Signaling. Early Transcriptional Control during Shade Avoidance Responses in Arabidopsis

• Published in: Plant physiology (Bethesda) Vol. 141; no. 1; pp. 85 - 96
• Main Authors: Roig-Villanova, Irma, Bou, Jordi, Sorin, Céline, Devlin, Paul F., Martínez-García, Jaime F.
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.05.2006; American Society of Plant Physiologists
• Subjects: Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis Proteins - physiology; Arabidopsis thaliana; Basic Helix-Loop-Helix Transcription Factors - genetics; Basic Helix-Loop-Helix Transcription Factors - physiology; Basic-Leucine Zipper Transcription Factors - genetics; Basic-Leucine Zipper Transcription Factors - physiology; Biological and medical sciences; Cell Biology and Signal Transduction; Cell physiology; Fundamental and applied biological sciences. Psychology; Gene expression regulation; Gene Expression Regulation, Plant; Genes; Glucuronidase - analysis; Homeodomain Proteins - genetics; Homeodomain Proteins - metabolism; Hypocotyls; Light; Molecular and cellular biology; Mutation; Nuclear Proteins - genetics; Nuclear Proteins - physiology; Phytochrome - metabolism; Plant cells; Plants; Promoter Regions, Genetic; Recombinant Fusion Proteins - metabolism; Regulator genes; Repression; Seedlings; Signal Transduction; Transcription Factors - genetics; Transcription Factors - metabolism; Transcription Factors - physiology; Transcriptional regulatory elements; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - physiology; Up regulation; β-Glucuronidase; Enzyme; Photoreceptor; Gene expression; Arabidopsis thaliana; Morphogenesis; Cycloheximide; Signal transduction; Gene; Cruciferae; Dicotyledones; Glycosidases; Angiospermae; Phytochrome; Development; Hydrolases; Spermatophyta; Mutation; O-Glycosidases; Canopy(vegetation)
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.105.076331

The phytochrome (phy) photoreceptors modulate plant development after perception of light. Upon illumination of etiolated seedlings, phys initiate a transcriptional cascade by directly transducing light signals to the promoters of genes encoding regulators of morphogenesis. In light-grown plants, however, little is known about the transcriptional cascade modulated by phys in response to changes in light. The phy entry points in this cascade are completely unknown. We are particularly interested in the shade avoidance syndrome (SAS). Here we describe a subset of six genes whose expression is rapidly modulated by phys during both deetiolation and SAS in Arabidopsis (Arabidopsis thaliana). Using cycloheximide, we provide evidence that four of these phy rapidly regulated (PAR) genes are direct targets of phy signaling during SAS, revealing these genes as upstream components of the transcriptional cascade. Promoter-β-glucuronidase fusions confirmed that PAR genes are photoregulated at the transcriptional level. Analysis of gene expression in light signal transduction mutants showed that COP1 and DET1 (but not DET2 or HY5) play a role in modulating PAR expression in response to shade in light-grown seedlings. Moreover, genetic analyses showed that one of the genes identified as a direct target of phy signaling was phy-interacting factor 3-like-1 (PIL1). PIL1 has previously been implicated in SAS in response to transient shade, but we show here that it also plays a key role in response to long-term shade. The action of PIL1 was particularly apparent in a phyB background, suggesting an important negative role for PIL1 under dense vegetation canopies.