DIFFERENTIAL PATTERNS OF EXPRESSION OF THE ARABIDOPSIS PHYB, PHYD, AND PHYE PHYTOCHROME GENES

The Arabidopsis thaliana phyB, phyD, and phyE phytochrome apoproteins show higher amino acid sequence similarity to each other than to phyA or phyC, they are the most recently evolved members of this photorecep tor family, and they may interact in regulating photomorphogenesis. Th e expression patterns of translational fusions of the 5' upstream regi ons of the PHYB, PHYD, and PHYE genes to the beta-glucuronidase (GUS) coding sequence were compared. P-D-GUS and P-E-GUS fusions were 5- to 10-fold less active than a P-B-GUS fusion, but all three promoter regi ons drove expression of the reporter gene in all stages of the plant's life cycle. Over the first 10 d of seedling growth, the PHYB and PHYD promoters were more active in the dark than in the light, whereas the opposite was true of the PHYE promoter. Unlike the P-B-GUS construct, which was expressed in most parts of seedlings and mature plants, the P-D-GUS and P-E-GUS transgenes showed differential expression, notabl y in leaves, flower organs, and root tips. Tissue sections showed that the three promoters are coexpressed in at least some leaf cells. Henc e, the PHYB, PHYD, and PHYE genes differ in expression pattern but the se patterns overlap and interaction of these receptor forms within ind ividual cells is possible.