THE PHYTOCHROME APOPROTEIN FAMILY IN ARABIDOPSIS IS ENCODED BY 5 GENES - THE SEQUENCES AND EXPRESSION OF PHYD AND PHYE

Two novel Arabidopsis phytochrome genes, PHYD and PHYE, are described and evidence is presented that, together with the previously described PHYA, PHYB and PHYC genes, the primary structures of the complete phy tochrome family of this plant are now known. The PHYD- and PHYE-encode d proteins are of similar size to the other phytochrome apoproteins an d show sequence similarity along their entire lengths. Hence, red/far- red light sensing in higher plants is mediated by a diverse but struct urally conserved group of soluble photoreceptors. The proteins encoded by the PHYD and PHYE genes are more closely related to phytochrome B than to phytochromes A or C, indicating that the evolution of the PHY gene family in Arabidopsis includes an expansion of a PHYB-related sub group. The PHYB and PHYD phytochromes show greater than 80% amino acid sequence identity but the phenotypes of phyB null mutants demonstrate that these receptor forms are not functionally redundant. The five PH Y 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 structu re and expression of a complete phytochrome family in a higher plant.