PIF1 is regulated by light-mediated degradation through the ubiquitin-26S proteasome pathway to optimize photomorphogenesis of seedlings in Arabidopsis

• Published in: The Plant journal : for cell and molecular biology 2005-12, Vol.44 (6), p.1023-1035
• Main Authors: Shen, H, Moon, J, Huq, E
• Format: Article
• Language: English
• Subjects: Arabidopsis - growth & development; Arabidopsis - metabolism; Arabidopsis - radiation effects; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Basic Helix-Loop-Helix Transcription Factors - metabolism; bHLH factor; biochemical pathways; Biological and medical sciences; Botany; far-red light; Flowers & plants; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; genetic complementation; helix-loop-helix motifs; Light; light signaling; Metabolism; Models, Biological; molecular sequence data; Morphogenesis - radiation effects; nucleotide sequences; Phenotype; phenotypic variation; photomorphogenesis; photoreceptor; photoreceptors; phytochrome; phytochrome interacting factor; plant biochemistry; plant ecology; plant physiology; Plant physiology and development; plant proteins; Plants, Genetically Modified - anatomy & histology; Plants, Genetically Modified - metabolism; Plants, Genetically Modified - radiation effects; proteasome endopeptidase complex; Proteasome Endopeptidase Complex - metabolism; protein degradation; Proteins; recombinant fusion proteins; Recombinant Fusion Proteins - metabolism; red light; seedling growth; seedlings; Seedlings - growth & development; Seedlings - metabolism; Seedlings - radiation effects; Seeds; signal transduction; Signal Transduction - genetics; Storage and secretion, pigments, phytochrome; transcription factors; transcriptional activation; ubiquitin; Ubiquitin - metabolism
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313x.2005.02606.x

Light signals perceived by the phytochrome (phy) family of sensory photoreceptors control multiple aspects of plant development. Recently, PIF1, a phy-interacting basic helix-loop-helix (bHLH) transcription factor, has been shown to negatively regulate facets of the photomorphogenesis of seedlings. Moreover, the transcriptional activation activity of PIF1 is reduced in a phy-dependent manner. In this study we use the luciferase (LUC) activity of the LUC-PIF1 fusion protein as an indicator of the stability of PIF1 in various light conditions. We found that the activity of LUC-PIF1 in both transient and stable transgenic lines is rapidly reduced in light, while the LUC-only control is stable under the same conditions, suggesting that PIF1 is degraded in response to light. Fluence-rate response curves indicate that PIF1 degradation is very sensitive to the quality and quantity of light. The half-life of PIF1 is about 16 min under 10 micromol m(-2) sec(-1) red light. PIF1 reaccumulates in the subsequent dark period after light-induced degradation, signifying that PIF1 not only functions in the dark and during the transition from etiolated to de-etiolated growth, but may also function during diurnal cycles. Inhibitors of the 26S proteasome increased the stability of PIF1, indicating that degradation of PIF1 is mediated by the ubiquitin-26S proteasome pathway. Further, de novo protein synthesis is not required for degradation of PIF1, as the presence of cycloheximide does not prevent degradation of PIF1 in the light. Taken together, these results suggest that the light signals perceived by phys induce the degradation of PIF1 and other phyinteracting factors to optimize photomorphogenesis.