Light-independent phytochrome signaling mediated by dominant GAF domain tyrosine mutants of Arabidopsis phytochromes in transgenic plants.
The photoreversibility of plant phytochromes enables continuous surveillance of the ambient light environment. Through expression of profluorescent, photoinsensitive Tyr-to-His mutant alleles of Arabidopsis thaliana phytochrome B (PHYB(Y276H)) and Arabidopsis phytochrome A (PHYA(Y242H)) in transgenic Arabidopsis plants, we demonstrate that photoconversion is not a prerequisite for phytochrome signaling. PHYB(Y276H)-expressing plants exhibit chromophore-dependent constitutive photomorphogenesis, light-independent phyB(Y276H) nuclear localization, constitutive activation of genes normally repressed in darkness, and light-insensitive seed germination. Fluence rate analyses of transgenic plants expressing PHYB(Y276H), PHYA(Y242H), and other Y(GAF) mutant alleles of PHYB demonstrate that a range of altered light-signaling activities are associated with mutation of this residue. We conclude that the universally conserved GAF domain Tyr residue, with which the bilin chromophore is intimately associated, performs a critical role in coupling light perception to signal transduction by plant phytochromes.
Section of Molecular and Cellular Biology, University of California, Davis, California 95616, USA.
Yi-shin
YS
Su
J Clark
JC
Lagarias
D000483:Alleles; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D001654:Bile Pigments / Q000378:metabolism; D022003:Cell Nucleus Structures / Q000528:radiation effects; D005799:Genes, Dominant; D017343:Genes, Plant; D005816:Genetic Complementation Test; D018525:Germination / Q000528:radiation effects; D008027:Light; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D017440:Photoperiod; D051942:Phytochrome A / Q000737:chemistry / Q000378:metabolism*; D051939:Phytochrome B / Q000737:chemistry / Q000378:metabolism*; D030821:Plants, Genetically Modified; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000528:radiation effects; D012639:Seeds / Q000378:metabolism / Q000528:radiation effects; D015398:Signal Transduction / Q000528:radiation effects*; D014170:Transformation, Genetic; D014443:Tyrosine / Q000235:genetics*
D001654:Bile Pigments; D050505:Mutant Proteins; D051942:Phytochrome A; D051939:Phytochrome B; D014443:Tyrosine