Journal Article

Light-Regulated Nuclear Import and Degradation of Arabidopsis Phytochrome-A N-Terminal Fragments

Iris Wolf, Stefan Kircher, Erzsébet Fejes, László Kozma-Bognár, Eberhard Schäfer, Ferenc Nagy and Éva Ádám

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 52, issue 2, pages 361-372
Published in print February 2011 | ISSN: 0032-0781
Published online December 2010 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcq194
Light-Regulated Nuclear Import and Degradation of Arabidopsis Phytochrome-A N-Terminal Fragments

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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The photoreceptor phytochrome-A (phyA) regulates germination and seedling establishment by mediating very low fluence (VLFR) and far-red high irradiance (FR-HIR) responses in Arabidopsis thaliana. In darkness, phyA homodimers exist in the biologically inactive Pr form and are localized in the cytoplasm. Light induces formation of the biologically active Pfr form and subsequent rapid nuclear import. PhyA Pfr, in contrast to the Pr form, is labile and has a half-life of ∼30 min. We produced transgenic plants in a phyA-201 null background that express the PHYA–yellow fluorescent protein (YFP) or the PHYA686–YFP–dimerization domain (DD) and PHYA686–YFP–DD–nuclear localization signal (NLS) or PHYA686–YFP–DD–nuclear exclusion signal (NES) fusion proteins. The PHYA686–YFP fusion proteins contained the N-terminal domain of phyA (686 amino acid residues), a short DD and the YFP. Here we report that (i) PHYA686–YFP–DD fusion protein is imported into the nucleus in a light-dependent fashion; (ii) neither of the PHYA686 fusion proteins is functional in FR-HIR and nuclear VLFR; and (iii) the phyA-dependent, blue light-induced inhibition of hypocotyl growth is mediated by the PHYA686–YFP–DD–NES but not by the PHYA686–YFP–DD–NLS and PHYA686–YFP–DD fusion proteins. We demonstrate that (i) light induces degradation of all PHYA N-terminal-containing fusion proteins and (ii) these N-terminal domain-containing fusion proteins including the constitutively nuclear PHYA686–YFP–DD–NLS and predominantly cytoplasmic PHYA686–YFP–DD–NES degrade at comparable rates but markedly more slowly than PHYA–YFP, whereas (iii) light-induced degradation of the native phyA is faster compared with PHYA–YFP.

Keywords: High irradiation response; Light-induced degradation; Nuclear import; Phytochrome-A; Signaling; Very low fluence response

Journal Article.  7003 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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