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Updated: Jun 30, 2026

Bimolecular Fluorescence Complementation (BiFC) Assay for Protein-Protein Interaction in Onion Cells Using the Helios Gene Gun
Published on: June 13, 2010
Phytochrome-interacting factor 1 is a critical bHLH regulator of chlorophyll biosynthesis
Enamul Huq1, Bassem Al-Sady, Matthew Hudson
1Section of Molecular Cell and Developmental Biology and Institute of Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA.
Abstract:
Photosynthetic organisms must achieve a delicate balance between the light energy absorbed by chlorophyll and their capacity to channel that energy into productive photochemical reactions. Release of excess absorbed energy in the cell can cause lethal photooxidative damage. We identified a basic helix-loop-helix (bHLH) transcription factor, designated PHYTOCHROME-INTERACTING FACTOR 1 (PIF1), that negatively regulates chlorophyll biosynthesis. pif1 mutant seedlings accumulate excess free protochlorophyllide when grown in the dark, with consequent lethal bleaching upon exposure to light. PIF1 interacts specifically with the photoactivated conformer of phytochromes A and B, suggesting a signaling pathway by which chlorophyll biosynthetic rates are tightly controlled during the critical initial emergence of seedlings from subterranean darkness into sunlight.
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