BRAINCAKEPhytochrome as a Transcription Factor
Phytochrome causes long-lasting changes in the plant, such as greening, by changing which genes are expressed.
Pr is found in the cytoplasm. When it absorbs red light and is converted to Pfr, the molecule changes shape. This exposes a signal that lets Pfr move through the nuclear pores into the nucleus.
In the nucleus, Pfr binds to proteins called phytochrome-interacting factors (PIFs). PIFs are transcription factors: they bind to the promoter regions of target genes and control whether RNA polymerase can transcribe them. In the dark, PIFs keep the seedling etiolated. When Pfr binds to them, the PIFs are tagged for breakdown, so the genes they were controlling are switched on or off.
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Key terms in this lesson
- phytochrome
- A blue-green plant pigment existing in two interconvertible forms sensitive to red and far-red light, controlling responses such as flowering and germination.
More in Chemical Control
- Long Day Plants
- Short Day Plants
- Day Neutral Plants
- Signal Detection
- Discovery
- Photomorphogenesis
- Germination and Photomorphogenesis
- Phytochromes, Photomorphogenesis and Tropisms
All 30 lessons in Chemical Control · All Edexcel A-level Biology topics