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First published online July 27, 2007; 10.1105/tpc.107.051516 The Plant Cell 19:2124-2139 (2007) © 2007 American Society of Plant Biologists OPEN ACCESS ARTICLE
Light-Independent Phytochrome Signaling Mediated by Dominant GAF Domain Tyrosine Mutants of Arabidopsis Phytochromes in Transgenic Plants[W],[OA]Section of Molecular and Cellular Biology, University of California, Davis, California 95616 1 Address correspondence to jclagarias{at}ucdavis.edu.
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 (PHYBY276H) and Arabidopsis phytochrome A (PHYAY242H) in transgenic Arabidopsis plants, we demonstrate that photoconversion is not a prerequisite for phytochrome signaling. PHYBY276H-expressing plants exhibit chromophore-dependent constitutive photomorphogenesis, light-independent phyBY276H nuclear localization, constitutive activation of genes normally repressed in darkness, and light-insensitive seed germination. Fluence rate analyses of transgenic plants expressing PHYBY276H, PHYAY242H, and other YGAF 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. Related articles in Plant Cell:
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