Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/1999
Publication Date: N/A
Citation: Quail, P.H., Halliday, K.J., Hudson, M., Ni, M., Qin, M. 1999. 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. Proceedings of the National Academy of Sciences 96(10):5832-5837. Interpretive Summary: These findings 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.
Technical Abstract: 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 dresponsiveness 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.