The phytochrome apoprotein family inArabidopsis is encoded by five genes: the sequences and expression ofPHYD andPHYE

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Abstract
Two novelArabidopsis phytochrome genes,PHYD andPHYE, are described and evidence is presented that, together with the previously describedPHYA, PHYB andPHYC genes, the primary structures of the complete phytochrome family of this plant are now known. ThePHYD- andPHYE-encoded proteins are of similar size to the other phytochrome apoproteins and show sequence similarity along their entire lengths. Hence, red/far-red light sensing in higher plants is mediated by a diverse but structurally conserved group of soluble photoreceptors. The proteins encoded by thePHYD andPHYE genes are more closely related to phytochrome B than to phytochromes A or C, indicating that the evolution of thePHY gene family inArabidopsis includes an expansion of a PHYB-related subgroup. The PHYB and PHYD phytochromes show greater than 80% amino acid sequence identity but the phenotypes ofphyB null mutants demonstrate that these receptor forms are not functionally redundant. The fivePHY mRNAs are, in general, expressed constitutively under varying light conditions, in different plant organs, and over the life cycle of the plant. These observations provide the first description of the structure and expression of a complete phytochrome family in a higher plant.