DOCSLIB.ORG

Download (8MB)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Download (8MB) Heilmann, Monika (2013) Structure-function studies of the UV-B photoreceptor UVR8 in Arabidopsis thaliana. PhD thesis. http://theses.gla.ac.uk/4067/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Glasgow Theses Service http://theses.gla.ac.uk/ [email protected] STRUCTURE-FUNCTION STUDIES OF THE UV-B PHOTORECEPTOR UVR8 IN ARABIDOPSIS THALIANA Monika Heilmann Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy Institute of Molecular, Cell and Systems Biology Faculty of Biomedical and Life Sciences University of Glasgow January 2013 © Monika Heilmann, 2013 SUMMARY SUMMARY Ultraviolet-B (UV-B) radiation is an integral component of natural sunlight reaching the Earth’s surface. Although being a potentially harmful and damaging agent, UV-B is a key environmental signal for plants initiating diverse responses that affect their metabolism, development and viability. The majority of these responses involve the differential regulation of gene expression and all require accurate perception of the effective light quality by a photoreceptor. The recent identification of UV RESISTANCE LOCUS8 (UVR8) as a UV-B photoreceptor has been an important milestone in plant UV-B research (Rizzini et al., 2011; Christie et al., 2012; Wu et al., 2012). However, rather little is known yet about the precise mechanisms of photoreception and signal transduction. Therefore, the overall aim of this study was to investigate how the structure of the UVR8 protein determines its function in the UV-B response in Arabidopsis. The mechanism of light perception by UVR8 differs from other so far characterized photoreceptors since UVR8 does not bind an external cofactor as chromophore but performs UV-B photoreception using some of its intrinsic tryptophans. To identify structurally and functionally important amino acids of UVR8, site-directed mutagenesis of a conserved and repeated motif GWRHT was carried out. The tryptophans of these motifs form the base of the postulated UV-B perceiving pyramid (Christie et al., 2012). The impact of the introduced mutations was assessed in vitro and in vivo by various methods such as size exclusion chromatography (SEC), far-UV circular dichroism (CD) spectroscopy and forms of polyacrylamide gel electrophoresis (PAGE). Results showed that in the absence of UV-B UVR8 forms a dimer that is very effectively held together by a network of cross-dimer salt bridges. Especially important for stable dimerisation were salt bridges that are located adjacent to the UV-B perceiving tryptophan pyramid, in particular those involving R286 and their disruption by mutation led to constitutive monomerisation of the photoreceptor. Several mutations resulted in a destabilized and weakened dimer which could only be detected as dimer in vitro but appeared monomeric in vivo. The currently most upstream identified event of UV-B perception by UVR8 is its UV-B induced monomerisation which happens very rapidly and in a fluence rate dependent manner (Rizzini et al., 2011). UV-B also causes physical interaction between UVR8 and CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1) which is essential to initiate UVR8-mediated signalling (Favory et al., 2009). Stable transgenic Arabidopsis lines expressing various UVR8 salt bridge mutants as GFP-fusions in the uvr8-1 background i SUMMARY were generated to analyse structural requirements of UVR8 for its interaction with COP1 and to test the photomorphogenic response with respect to UV-B induction of ELONGATED HYPOCOTYL5 (HY5 ) and CHALCONE SYNTHASE (CHS ) gene expression and suppression of hypocotyl extension. The results established that, in vivo, constitutive monomerisation and constitutive interaction with COP1 are not sufficient to initiate a UVR8-mediated response in the absence of UV-B. Furthermore, a constitutively monomeric mutant that still showed a photomorphogenic response in the presence of UV-B could be identified, suggesting that dimerisation is not required for UV-B perception and UVR8-mediated signalling in vivo. One characteristic feature of the UV-B perceiving tryptophan pyramid is that the close proximity of the aromatic side chains allows overlap of their electronic orbitals resulting in exciton coupling of the tryptophans which could be monitored by far-UV CD spectroscopy (Christie et al., 2012). Exciton coupling was absent after UV-B induced monomerisation and was reduced in several salt bridge mutants. The close proximity of UV-B perceiving tryptophan residues to essential dimer maintaining salt bridges led to the hypothesis that electron transfer may occur between the tryptophans and adjacent salt-bridging arginines leading to charge neutralization and thus dimer destabilization and monomerisation (Christie et al., 2012). Fourier transform infrared (FTIR) spectroscopy was employed to detect UV-B induced changes in the chemical structure of the amino acid side chains and the overall conformation of the protein. However, the signals obtained in the light-induced difference spectra could not be clearly assigned to a specific process and require further experiments. Changes in the local environment of the tryptophan chromophore could be detected by fluorescence spectroscopy. Here, a UV-B induced red shift of the protein’s emission spectrum was observed which shows that the initially buried tryptophan pyramid becomes solvent exposed, which is consistent with UV-B induced monomerisation. UV-B induced conformational changes of the photoreceptor’s C-terminus were revealed by limited proteolysis experiments. The pattern of peptides produced by mild trypsin digestion of UVR8, which are derived from the C-terminus, changes after UV-B exposure suggesting that UV-B not only induces monomerisation but also conformational changes in the C-terminus that lead to changes in its accessibility. Those changes are required for activation of the signalling pathway as seen in vivo. Finally, to allow regulation of UVR8 signal transduction and an optimally balanced UV-B response, the activated monomeric form must return to its homodimeric ground state once UV-B is no longer present. This process had so far not been investigated and therefore the kinetics of dimer regeneration were analysed in various Arabidopsis genotypes and under ii SUMMARY influence of a protein synthesis inhibitor as well as an inhibitor of proteasomal activity. The level of total UVR8 protein remained unchanged in the presence of these inhibitors and also the kinetics of dimer regeneration were only slightly affected, which suggests that regeneration of dimeric UVR8 occurs by reversion from the monomer to the dimer. Regeneration of the UVR8 dimer was also possible in vitro with illuminated plant extract or purified UVR8 but was considerably slower, suggesting that the presence of intact cells is required. The absence of the C-terminus, which is known to interact with COP1 and REPRESSOR OF UV-B PHOTOMORPHOGENESIS (RUP) 1 and 2 (Cloix et al., 2012), had the greatest effect in slowing regeneration of the dimer in vivo but did not completely prevent it. The present study has extended our understanding of UV-B perception and signal transduction by UVR8 in plants in several respects and even if many questions still remain to be answered, slowly, the position and role of UVR8 in the great network of light signal transduction is emerging. iii TABLE OF CONTENTS TABLE OF CONTENTS FIGURES AND TABLES _________________________________________________ vii PREFACE ______________________________________________________________ x ACKNOWLEDGMENTS __________________________________________________ xi ABBREVIATIONS ______________________________________________________ xii 1. INTRODUCTION ____________________________________________________ 1 1.1 Impact of the sunlight spectrum on plants _______________________________ 1 1.2 Visible light perception and signalling responses in Arabidopsis _____________ 2 1.3 UV-B radiation and its biological effects ________________________________ 7 1.4 UVR8 – a UV-B photoreceptor ______________________________________ 12 1.5 COP1 – a central switch of light signal transduction ______________________ 18 1.6 Negative feedback regulation of light signalling pathways _________________ 21 1.7 Conclusion ______________________________________________________ 23 1.8 Aims of this study _________________________________________________ 24 2. MATERIAL AND METHODS ________________________________________ 26 2.1 Materials ________________________________________________________ 26 2.2 Preparation of media and solutions ___________________________________ 27 2.3 Plant material ____________________________________________________ 28 2.4 Treatments ______________________________________________________ 29 2.5 Bacterial transformation ____________________________________________ 31 2.6 DNA and RNA methods ____________________________________________ 32 2.7 Semi-quantitative Reverse Transcriptase PCR (RT-PCR) __________________ 35 2.8 Protein methods __________________________________________________ 36 2.9 Generation of stable transgenic Arabidopsislines
Load more

Recommended publications
  • UV-B Detected by the UVR8 Photoreceptor Antagonizes Auxin Signaling and Plant Shade Avoidance
    UV-B detected by the UVR8 photoreceptor antagonizes auxin signaling and plant shade avoidance Scott Hayesa, Christos N. Velanisb, Gareth I. Jenkinsb, and Keara A. Franklina,1 aSchool of Biological Sciences, University of Bristol, Bristol BS8 1UG, United Kingdom and bInstitute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom Edited by Mark Estelle, University of California, San Diego, La Jolla, CA, and approved June 23, 2014 (received for review February 18, 2014) Plants detect different facets of their radiation environment via leaf expansion in the presence of UV-B in a UVR8-dependent specific photoreceptors to modulate growth and development. manner (Fig. S2A). Along with the architectural responses, UV-B is perceived by the photoreceptor UV RESISTANCE LOCUS 8 UV-B perceived by UVR8 also partially inhibited the low (UVR8). The molecular mechanisms linking UVR8 activation to R:FR-mediated acceleration of flowering characteristic of shade plant growth are not fully understood, however. When grown in avoidance (Fig. S2B). close proximity to neighboring vegetation, shade-intolerant plants Low R:FR induces striking stem (hypocotyl) elongation in initiate dramatic stem elongation to overtop competitors. Here we seedlings (Fig. 2 A and B). Thus, we investigated the effect of UV-B show that UV-B, detected by UVR8, provides an unambiguous on this response. UV-B strongly inhibited low R:FR-mediated sunlight signal that inhibits shade avoidance responses in Arabi- hypocotyl elongation in a UVR8-dependent manner (Fig. 2 A dopsis thaliana by antagonizing the phytohormones auxin and and B).
    [Show full text]
  • O'hara, Andrew (2012) the Importance of Specific Tryptophans to UVR8 Function: an Intrinsic Chromophore for a UV-B Photoreceptor
    O'Hara, Andrew (2012) The importance of specific tryptophans to UVR8 function: an intrinsic chromophore for a UV-B photoreceptor. PhD thesis. http://theses.gla.ac.uk/4012/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Glasgow Theses Service http://theses.gla.ac.uk/ [email protected] THE IMPORTANCE OF SPECIFIC TRYPTOPHANS TO UVR8 STRUCTURE AND FUNCTION: AN INTRINSIC CHROMOPHORE FOR A UV-B PHOTORECEPTOR By Andrew O’Hara Thesis submitted for the degree of Doctor of Philosophy College of Medical, Veterinary & Life Sciences Institute of Molecular, Cell and Systems Biology University of Glasgow August, 2012 © Andrew O’Hara, 2012 I “This new power for the driving of the world’s machinery will be derived from the energy which operates the universe, the cosmic energy, whose central source for the earth is the sun and which is everywhere present in unlimited quantities” Nikola Tesla “What is a weed? A plant whose virtues have not yet been discovered” Ralph Waldo Emerson II To my Mum and Dad, Elizabeth and Thomas O’Hara and my son Ben III CONTENTS Title………………………………………………………………………………………
    [Show full text]
  • Regulation of UVR8 Photoreceptor Dimer/Monomer Photo-Equilibrium
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Enlighten Plant, Cell & Environment (2016) 39,1706–1714 doi: 10.1111/pce.12724 Original Article Regulation of UVR8 photoreceptor dimer/monomer photo- equilibrium in Arabidopsis plants grown under photoperiodic conditions Kirsten M.W. Findlay & Gareth I. Jenkins Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, UK ABSTRACT 2009). Moreover, UV-B wavelengths in sunlight are important in regulating a wide range of plant processes, including meta- The UV RESISTANCE LOCUS 8 (UVR8) photoreceptor bolic activities, morphogenesis, photosynthetic competence specifically mediates photomorphogenic responses to UV-B. and defence against pests and pathogens (Jordan 1996; Jenkins Photoreception induces dissociation of dimeric UVR8 into 2009; Ballaré et al. 2012; Robson et al. 2014). It is therefore im- monomers to initiate responses. However, the regulation of portant to understand the cellular and molecular mechanisms dimer/monomer status in plants growing under photoperiodic that enable plants to detect and respond to UV-B. conditions has not been examined. Here we show that UVR8 UV-B exposure stimulates the differential expression of hun- establishes a dimer/monomer photo-equilibrium in plants dreds of plant genes (Casati & Walbot 2004; Ulm et al. 2004; growing in diurnal photoperiods in both controlled environ- Brown et al. 2005; Kilian et al. 2007; Favory et al. 2009). In many ments and natural daylight. The photo-equilibrium is cases these responses are initiated by activation of non-UV-B- determined by the relative rates of photoreception and specific signalling pathways, involving DNA damage or in- dark-reversion to the dimer.
    [Show full text]
  • Phytochrome Diversity in Green Plants and the Origin of Canonical Plant Phytochromes
    ARTICLE Received 25 Feb 2015 | Accepted 19 Jun 2015 | Published 28 Jul 2015 DOI: 10.1038/ncomms8852 OPEN Phytochrome diversity in green plants and the origin of canonical plant phytochromes Fay-Wei Li1, Michael Melkonian2, Carl J. Rothfels3, Juan Carlos Villarreal4, Dennis W. Stevenson5, Sean W. Graham6, Gane Ka-Shu Wong7,8,9, Kathleen M. Pryer1 & Sarah Mathews10,w Phytochromes are red/far-red photoreceptors that play essential roles in diverse plant morphogenetic and physiological responses to light. Despite their functional significance, phytochrome diversity and evolution across photosynthetic eukaryotes remain poorly understood. Using newly available transcriptomic and genomic data we show that canonical plant phytochromes originated in a common ancestor of streptophytes (charophyte algae and land plants). Phytochromes in charophyte algae are structurally diverse, including canonical and non-canonical forms, whereas in land plants, phytochrome structure is highly conserved. Liverworts, hornworts and Selaginella apparently possess a single phytochrome, whereas independent gene duplications occurred within mosses, lycopods, ferns and seed plants, leading to diverse phytochrome families in these clades. Surprisingly, the phytochrome portions of algal and land plant neochromes, a chimera of phytochrome and phototropin, appear to share a common origin. Our results reveal novel phytochrome clades and establish the basis for understanding phytochrome functional evolution in land plants and their algal relatives. 1 Department of Biology, Duke University, Durham, North Carolina 27708, USA. 2 Botany Department, Cologne Biocenter, University of Cologne, 50674 Cologne, Germany. 3 University Herbarium and Department of Integrative Biology, University of California, Berkeley, California 94720, USA. 4 Royal Botanic Gardens Edinburgh, Edinburgh EH3 5LR, UK. 5 New York Botanical Garden, Bronx, New York 10458, USA.
    [Show full text]
  • UVR8 Interacts with WRKY36 to Regulate HY5 Transcription and Hypocotyl Elongation in Arabidopsis
    ARTICLES https://doi.org/10.1038/s41477-017-0099-0 UVR8 interacts with WRKY36 to regulate HY5 transcription and hypocotyl elongation in Arabidopsis Yu Yang1,2, Tong Liang1,2, Libo Zhang1, Kai Shao1,2, Xingxing Gu1,2, Ruixin Shang1,2, Nan Shi1, Xu Li1, Peng Zhang1 and Hongtao Liu 1* UV RESISTANCE LOCUS 8 (UVR8) is an ultraviolet-B (UVB) radiation photoreceptor that mediates light responses in plants. How plant UVR8 acts in response to UVB light is not well understood. Here, we report the identification and characteriza- tion of the Arabidopsis WRKY DNA-BINDING PROTEIN 36 (WRKY36) protein. WRKY36 interacts with UVR8 in yeast and Arabidopsis cells and it promotes hypocotyl elongation by inhibiting HY5 transcription. Inhibition of hypocotyl elongation under UVB requires the inhibition of WRKY36. WRKY36 binds to the W-box motif of the HY5 promoter to inhibit its transcription, while nuclear localized UVR8 directly interacts with WRKY36 to inhibit WRKY36–DNA binding both in vitro and in vivo, leading to the release of inhibition of HY5 transcription. These results indicate that WRKY36 is a negative regulator of HY5 and that UVB represses WRKY36 via UVR8 to promote the transcription of HY5 and photomorphogenesis. The UVR8–WRKY36 interac- tion in the nucleus represents a novel mechanism of early UVR8 signal transduction in Arabidopsis. ltraviolet-B light is an inherent part of sunlight, which has ner1,6,16,17,22. The central role of HY5 in the UVB acclimation response significant biological effects on plants. Low-level, non-dam- is further confirmed by the UVB stress hypersensitive phenotype of aging UVB serves as a photomorphogenic signal to regu- the hy5 mutant1,16,21.
    [Show full text]
  • PL101 Vitamin D and Photoprotection
    and/or necrotic cell death) and secondary effects (i.e., damage to PL101 the vasculature and inflammatory reaction ending in the systemic Vitamin D and photoprotection: progress to date immunity). In recent times, more and more efforts are addressed Katie Marie Dixon to recognize the better PS employing in cancer PDT. Rose Department of Anatomy and Histology, Bosch Institute, Bengal Acetate (RBAc), administrated for 60 minutes at 10-5M University of Sydney, Sydney, NSW, Australia 2 and activated with 1,6 J/cm green light, is a powerful PS. It is Vitamin D compounds are produced in the skin following able to initiate in HeLa cells several signaling processes leading exposure to ultraviolet radiation (UVR). We previously reported to rapid, independent, successive, long-lasting and time-related that vitamin D compounds protect against UVR-induced cell onset of apoptosis and autophagic cell death by signals death and DNA damage (cyclobutane pyrimidine dimers; CPD originating from or converging on almost all intracellular and 8-oxoguanine) in cultured human skin cells. We have further organelles, i.e. mitochondria, lysosomes, Golgi apparatus and evidence that these photoprotective effects are mediated by the ER, despite RBAc primary perinuclear localization. Particularly, non-genomic pathway for vitamin D. We used an in vivo model apoptosis occurs as early as 1h after PDT via activation of to investigate the photoprotective effects of topical 1,25- intrinsic pathway, followed by activation of extrinsic, caspase- dihydroxyvitamin D3 (1,25D) and low calcemic analogs 12-dependent and caspase-independent pathways. The clearance (including a non-genomic agonist) in Skh:hr-1 mice exposed to 3 of RBAc photokilled HeLa cells, in terms of recruitment, MED of UVR, showing significant reductions in apoptotic recognition and removal, is very efficient both in vitro and in sunburn cells (SBCs) and CPDs.
    [Show full text]
  • Proline 411 Biases the Conformation of the Intrinsically Disordered Plant
    www.nature.com/scientificreports OPEN Proline 411 biases the conformation of the intrinsically disordered plant UVR8 photoreceptor C27 domain Received: 2 July 2018 Accepted: 28 November 2018 altering the functional properties of Published: xx xx xxxx the peptide Min Wu1,3, Daniel Farkas1,2, Leif A. Eriksson 1 & Åke Strid 2 UVR8 (UV RESISTANCE LOCUS 8) is a UV-B photoreceptor responsible for initiating UV-B signalling in plants. UVR8 is a homodimer in its signalling inactive form. Upon absorption of UV radiation, the protein monomerizes into its photoactivated state. In the monomeric form, UVR8 binds the E3 ubiquitin ligase COP1 (CONSTITUTIVELY PHOTOMORPHOGENIC 1), triggering subsequent UV- B-dependent photomorphogenic development in plants. Recent in vivo experiments have shown that the UVR8 C-terminal region (aa 397–423; UVR8C27) alone is sufcient to regulate the activity of COP1. In this work, CD spectroscopy and NMR experiments showed that the UVR8C27 domain was non-structured but gained secondary structure at higher temperatures leading to increased order. Bias-exchange metadynamics simulations were also performed to evaluate the free energy landscape of UVR8C27. An inverted free energy landscape was revealed, with a disordered structure in the global energy minimum. Flanking the global energy minimum, more structured states were found at higher energies. Furthermore, stabilization of the low energy disordered state was attributed to a proline residue, P411, as evident from P411A mutant data. P411 is also a key residue in UVR8 binding to COP1. UVR8C27 is therefore structurally competent to function as a molecular switch for interaction of UVR8 with diferent binding partners since at higher free energies diferent structural conformations are being induced in this peptide.
    [Show full text]
  • UVR8 Disrupts Stabilisation of PIF5 by COP1 to Inhibit Plant Stem Elongation in Sunlight
    Sharma, A., Sharma, B., Hayes, S., Kerner, K., Hoecker, U., Jenkins, G. I., & Franklin, K. A. (2019). UVR8 disrupts stabilisation of PIF5 by COP1 to inhibit plant stem elongation in sunlight. Nature Communications, 10, [4417 (2019)]. https://doi.org/10.1038/s41467- 019-12369-1, https://doi.org/10.1038/s41467-019-12369-1 Publisher's PDF, also known as Version of record License (if available): CC BY Link to published version (if available): 10.1038/s41467-019-12369-1 10.1038/s41467-019-12369-1 Link to publication record in Explore Bristol Research PDF-document This is the final published version of the article (version of record). It first appeared online via Springer Nature at https://www.nature.com/articles/s41467-019-12369-1. Please refer to any applicable terms of use of the publisher. University of Bristol - Explore Bristol Research General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/red/research-policy/pure/user-guides/ebr-terms/ ARTICLE https://doi.org/10.1038/s41467-019-12369-1 OPEN UVR8 disrupts stabilisation of PIF5 by COP1 to inhibit plant stem elongation in sunlight Ashutosh Sharma 1, Bhavana Sharma1, Scott Hayes 2, Konstantin Kerner3, Ute Hoecker3, Gareth I. Jenkins4 & Keara A. Franklin1* Alterations in light quality significantly affect plant growth and development. In canopy shade, phytochrome photoreceptors perceive reduced ratios of red to far-red light (R:FR) and initiate 1234567890():,; stem elongation to enable plants to overtop competitors.
    [Show full text]
  • Arabidopsis RUP2 Represses UVR8-Mediated Flowering in Noninductive Photoperiods
    Downloaded from genesdev.cshlp.org on October 2, 2021 - Published by Cold Spring Harbor Laboratory Press Arabidopsis RUP2 represses UVR8- mediated flowering in noninductive photoperiods Adriana B. Arongaus,1 Song Chen,1 Marie Pireyre,1 Nina Glöckner,2 Vinicius C. Galvão,3 Andreas Albert,4 J. Barbro Winkler,4 Christian Fankhauser,3 Klaus Harter,2 and Roman Ulm1,5 1Department of Botany and Plant Biology, Section of Biology, Faculty of Sciences, University of Geneva, 1211 Geneva 4, Switzerland; 2Department of Plant Physiology, Center for Plant Molecular Biology (ZMBP), University of Tübingen, 72076 Tübingen, Germany; 3Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland; 4Research Unit Environmental Simulation, Helmholtz Zentrum München, 85764 Neuherberg, Germany; 5Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, 1211 Geneva 4, Switzerland Plants have evolved complex photoreceptor-controlled mechanisms to sense and respond to seasonal changes in day length. This ability allows plants to optimally time the transition from vegetative growth to flowering. UV-B is an important part intrinsic to sunlight; however, whether and how it affects photoperiodic flowering has remained elusive. Here, we report that, in the presence of UV-B, genetic mutation of REPRESSOR OF UV-B PHOTOMOR- PHOGENESIS 2 (RUP2) renders the facultative long day plant Arabidopsis thaliana a day-neutral plant and that this phenotype is dependent on the UV RESISTANCE LOCUS 8 (UVR8) UV-B photoreceptor. We provide evidence that the floral repression activity of RUP2 involves direct interaction with CONSTANS, repression of this key activator of flowering, and suppression of FLOWERING LOCUS T transcription.
    [Show full text]
  • A UV-B-Specific Signaling Component Orchestrates Plant UV Protection
    A UV-B-specific signaling component orchestrates plant UV protection Bobby A. Brown*†, Catherine Cloix*†, Guang Huai Jiang*‡, Eirini Kaiserli*, Pawel Herzyk§, Daniel J. Kliebenstein¶, and Gareth I. Jenkins*ʈ *Plant Science Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, and §Sir Henry Wellcome Functional Genomics Facility and Division of Biochemistry and Molecular Biology, University of Glasgow, Glasgow G12 8QQ, United Kingdom; and ¶Department of Plant Sciences, University of California, Davis, CA 95616 Edited by Alexander N. Glazer, University of California System, Oakland, CA, and approved October 20, 2005 (received for review August 22, 2005) UV-B radiation in sunlight has diverse effects on humans, animals, genes are involved, for instance in ameliorating oxidative stress and plants, and microorganisms. UV-B can cause damage to molecules repairing UV damage. Mutants lacking UV-protective compo- and cells, and consequently organisms need to protect against and nents, such as the flavonoids and sinapic acid esters, are highly repair UV damage to survive in sunlight. In plants, low nondam- sensitive to ambient levels of UV-B (13, 14). aging levels of UV-B stimulate transcription of genes involved in Although plant responses to low ambient fluence rates of UV-B UV-protective responses. However, remarkably little is known are key to survival, the underlying mechanisms of UV-B perception about the underlying mechanisms of UV-B perception and signal and signal transduction are very poorly understood, despite decades transduction. Here we report that Arabidopsis UV RESISTANCE of research. These responses are not mediated by the known plant LOCUS 8 (UVR8) is a UV-B-specific signaling component that or- photoreceptors and do not involve DNA damage signaling path- chestrates expression of a range of genes with vital UV-protective ways (5, 6).
    [Show full text]
  • Sunhats for Plants How Plants Detect Dangerous Ultraviolet Rays Anyone Who Has Ever Suffered Sunburn Will Know About the Effects
    Sunhats for plants How plants detect dangerous ultraviolet rays Anyone who has ever suffered sunburn will know about the effects of too much ultraviolet (UV) radiation, in particular UV-B (from 280-315 nm in wavelength). Light in this region of the spectrum causes sunburn and DNA damage which may eventually lead to skin cancer. Humans are able to avoid excessive exposure to UV using a variety of tactics: applying sun block, wearing a sunhat or simply moving into the shade (or, more drastically, relocating to England). UV-B-induced DNA damage is a problem for all organisms that are exposed to bright sunlight, including plants, which have no option but to stay out in the midday sunshine without even the option of putting on a hat. As Kermit the Frog observed, it’s not easy being green! Because they can’t physically avoid UV-B, plants must detect high levels of UV-B light at a molecular level to protect against DNA damage and to repair any damage which may occur. The molecule responsible for detecting UV-B is a protein called UVR8. Structures of UVR8 (PDB 4d9s and 4dnw) from the model organism Arabidopsis thaliana have shed light on how this protein senses UV-B radiation and transduces that signal to activate photoprotective mechanisms. A propeller with a new twist UVR8 has a seven-bladed β-propeller fold (view 1) containing seven “regulator of chromosome condensation” (RCC1) Pfam sequence motifs that form the blades of the propeller. Proteins in this family are ubiquitous in eukaryotes and are known to bind to chromatin.
    [Show full text]
  • Conversion from CUL4-Based COP1–SPA E3 Apparatus to UVR8–COP1–SPA Complexes Underlies a Distinct Biochemical Function of COP1 Under UV-B
    Conversion from CUL4-based COP1–SPA E3 apparatus to UVR8–COP1–SPA complexes underlies a distinct biochemical function of COP1 under UV-B Xi Huanga,b, Xinhao Ouyanga,b,c, Panyu Yanga,d, On Sun Laub,1, Liangbi Chend, Ning Weib, and Xing Wang Denga,b,2 aPeking–Yale Joint Center for Plant Molecular Genetics and Agro-Biotechnology, National Laboratory of Protein Engineering and Plant Genetic Engineering, College of Life Sciences, Peking University, Beijing 100871, China; bDepartment of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT, 06520-8104; cRice Research Institute, Sichuan Agricultural University, Chengdu, Sichuan 611130, China; and dDepartment of Botany, College of Life Sciences, Hunan Normal University, Changsha 410081, China Contributed by Xing Wang Deng, September 4, 2013 (sent for review August 14, 2013) The evolutionarily conserved CONSTITUTIVE PHOTOMORPHOGENESIS either COP1 or HY5 has previously been shown to result in de- 1 (COP1) is a RING and WD40 protein that functions as a substrate creased activation of UV-B–responsive genes, impaired photo- receptor of CULLIN4–DAMAGED DNA BINDING PROTEIN 1 (CUL4– morphogenesis, and defective UV-B acclimation (11, 12). Both DDB1)–based E3 ubiquitin ligases in both plants and animals. In COP1 and HY5 localize in the nucleus under UV-B (11). The UV- Arabidopsis, COP1 is a central repressor of photomorphogenesis B–induced HY5 expression is largely dependent on UVR8 and in the form of COP1–SUPPRESSOR OF PHYA (SPA) complex(es). COP1 (8, 11, 13), and HY5 undertakes a positive feedback on COP1 CUL4–DDB1–COP1–SPA suppresses the photomorphogenic program by targeting the COP1 promoter for the UV-B–mediated activation by targeting the transcription factor ELONGATED HYPOCOTYL 5 for (9).
    [Show full text]