Phytochrome (PHY)

Phytochromes are a class of photoreceptor proteins found in plants, bacteria, and fungi that sense red and far-red light to coordinate various physiological and developmental processes. They consist of a protein backbone covalently linked to a light-sensing chromophore, typically a linear tetrapyrrole such as phytochromobilin or phycocyanobilin, which undergoes a conformational change upon light absorption. In plants, phytochromes are essential for photomorphogenesis, regulating critical life-cycle transitions including seed germination, seedling de-etiolation, and the induction of flowering. While phytochromes are not present in humans and thus are not traditional pharmacological targets for human disease, they have gained significant prominence in biotechnology as a core component of optogenetic tools. Researchers utilize phytochrome-based systems in mammalian cells to achieve precise, light-mediated control over gene expression and protein-protein interactions, making them invaluable in synthetic biology and fundamental biomedical research.

Other names

PHYAPHYBPHYCPHYDPHYERed/far-red light photoreceptorChromoprotein

Phytochromes function through a light-induced reversible photoisomerization of a covalently bound tetrapyrrole chromophore, switching the protein between an inactive red-light-absorbing (Pr) state and an active far-red-light-absorbing (Pfr) state, which then modulates signaling pathways often involving translocation to the nucleus and interaction with transcription factors like PIFs (Phytochrome Interacting Factors).