InterPro domain: IPR001294

Phytochromes are a class of photoreceptor found in plants, bacteria and fungi, which are used to detect light. In plants, phytochromes mediate physiological and developmental responses to changes in red and far-red light conditions [ 1 ].The protein undergoes reversible photochemical conversion between a biologically-inactive red light-absorbing form and the active far-red light-absorbing form. Phytochrome is a dimer of identical 124kDa subunits, each of which contains a linear tetrapyrrole chromophore, covalently-attached via a Cys residue.

In Arabidopsis thaliana, there are genes for at least five phytochrome proteins [ 2 ].These photoreceptors control such responses as germination, stem elongation, flowering, gene expression, and chloroplast and leaf development. It is not yet known which red light responses are controlled by which phytochrome species, or whether the different phytochromes have overlapping functions [ 3 ]. Synechocystis sp. (strain PCC 6803) hypothetical protein slr0473 contains a domain similar to that of plants phytochrome and seems also to bind a chromophore.

1. Phytochrome: a light-activated molecular switch that regulates plant gene expression. Annu. Rev. Genet. 25, 389-409
2. Novel phytochrome sequences in Arabidopsis thaliana: structure, evolution, and differential expression of a plant regulatory photoreceptor family. Genes Dev. 3, 1745-57
3. Mutations in the gene for the red/far-red light receptor phytochrome B alter cell elongation and physiological responses throughout Arabidopsis development. Plant Cell 5, 147-57