Identification of primary target genes of phytochrome signaling. Early transcriptional control during shade avoidance responses in Arabidopsis.
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-beta-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.
Departament de Genètica Molecular, Institut de Biologia Molecular de Barcelona, Consorci CSIC-IRTA, 08034 Barcelona, Spain.
Irma
I
Roig-Villanova
Jordi
J
Bou
Céline
C
Sorin
Paul F
PF
Devlin
Jaime F
JF
Martínez-García
D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000502:physiology; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000502:physiology; D018506:Gene Expression Regulation, Plant; D005966:Glucuronidase / Q000032:analysis; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008027:Light; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology; D010834:Phytochrome / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000502:physiology
D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D005966:Glucuronidase; D018398:Homeodomain Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D010834:Phytochrome; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D044767:Ubiquitin-Protein Ligases; C080210:ATHB-2 protein, Arabidopsis; C088435:DET1 protein, Arabidopsis; C098907:DET2 protein, Arabidopsis; C109254:HY5 protein, Arabidopsis; C524961:PAR1 protein, Arabidopsis; C456844:PIL1 protein, Arabidopsis; C471983:AT2G32950 protein, Arabidopsis