poc1: An Arabidopsis Mutant Perturbed in Phytochrome Signaling because of a T DNA Insertion in the Promoter of PIF3, a Gene Encoding a Phytochrome-Interacting bHLH Protein

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 96; no. 10; pp. 5832 - 5837
• Main Authors: Halliday, Karen J., Hudson, Matthew, Ni, Min, Qin, Minmin, Quail, Peter H.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 11.05.1999; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Subjects: Arabidopsis; Arabidopsis - genetics; Arabidopsis Proteins; Basic Helix-Loop-Helix Transcription Factors; Biological Sciences; Botany; Cloning, Molecular; Deoxyribonucleic acid; DNA; DNA, Bacterial - genetics; Flowers & plants; Gene Expression Regulation, Plant - genetics; Genes; Genes, Plant; Genetic loci; Genomics; Helix-Loop-Helix Motifs; Hypocotyl - metabolism; Hypocotyls; Light; Mutagenesis, Insertional; Mutation; Phenotype; Phenotypes; Photoreceptor Cells; Photoreceptors; Phytochrome - genetics; Phytochrome B; Polymerase chain reaction; Polymorphism, Restriction Fragment Length; Promoter Regions, Genetic; Proteins; RNA, Messenger - metabolism; Seedlings; Signal Transduction; Transcription Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.96.10.5832

The phytochrome family of informational photoreceptors has a central role in regulating light-responsive gene expression, but the mechanism of intracellular signal transduction has remained elusive. In a genetic screen for T DNA-tagged Arabidopsis mutants affected in early signaling intermediates, we identified poc1 (photocurrent 1), which exhibits enhanced responsiveness to red light. This phenotype is absent in a phyB (phytochrome B) null mutant background, indicating that the poc1 mutation enhances phyB signal transduction. The T DNA insertion in poc1 was found to be located in the promoter region of PIF3, a gene encoding a basic helix-loop-helix protein. The mutant phenotype seems to result from insertion-induced overexpression of this gene in red-light-grown seedlings, consistent with PIF3 functioning as a positively acting signaling intermediate. These findings, combined with data from a separate yeast two-hybrid screen that identified PIF3 as a phytochrome-interacting factor necessary for normal signaling, provide evidence that phytochrome signal transduction may include a direct pathway to photoresponsive nuclear genes via physical interaction of the photoreceptor molecules with the potential transcriptional regulator PIF3.