Bio

Professional Education


  • Doctor of Philosophy, Kjobenhavns Universitet (2011)
  • Diplom, Johannes Gutenberg Universitat Mainz (2008)
  • Master of Science, Lunds Universitet (2007)

Stanford Advisors


Publications

Journal Articles


  • Characterization of Mutations in Barley fch2 Encoding Chlorophyllide a Oxygenase PLANT AND CELL PHYSIOLOGY Mueller, A. H., Dockter, C., Gough, S. P., Lundqvist, U., von Wettstein, D., Hansson, M. 2012; 53 (7): 1232-1246

    Abstract

    The barley (Hordeum vulgare L.) mutants fch2 and clo-f2 comprise an allelic group of 14 Chl b-deficient lines. The genetic map position of fch2 corresponds to the physical map position of the gene encoding chlorophyllide a oxygenase. This enzyme converts chlorophyllide a to chlorophyllide b and it is essential for Chl b biosynthesis. The fch2 and clo-f2 barley lines were shown to be mutated in the gene for chlorophyllide a oxygenase. A five-base insertion was found in fch2 and base deletions in clo-f2.101, clo-f2.105, clo-f2.2800 and clo-f2.3613. In clo-f2.105 and clo-f2.108, nonsense base exchanges were discovered. All of these mutations led to a premature stop of translation and none of the mutants formed Chl b. The mutant clo-f2.2807 was transcript deficient and formed no Chl b. Missense mutations in clo-f2.102 (leading to the amino acid exchange D495N) and clo-f2.103 (G280D) resulted in a total lack of Chl b, whereas in the missense mutants clo-f2.107 (P419L), clo-f2.109 (A94T), clo-f2.122 (C320Y), clo-f2.123 (A94T), clo-f2.133 (A376V) and clo-f2.181 (L373F) intermediate contents of Chl b were determined. The missense mutations affect conserved residues, and their effect on chlorophyllide a oxygenase is discussed. The mutations in clo-f2.102, clo-f2.103, clo-f2.133 and clo-f2.181 may influence electron transfer as illustrated in the active site of a structural model protein. The changes in clo-f2.107, clo-f2.109, clo-f2.122 and clo-f2.123 may lead to Chlb deficiency by interfering with the regulation of chlorophyllide a oxygenase. The correlation of mutations and phenotypes strongly supports that the barley locus fch2 encodes chlorophyllide a oxygenase.

    View details for DOI 10.1093/pcp/pcs062

    View details for Web of Science ID 000306372000006

    View details for PubMedID 22537757

  • Induced mutations in circadian clock regulator Mat-a facilitated short-season adaptation and range extension in cultivated barley PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Zakhrabekova, S., Gough, S. P., Braumann, I., Muller, A. H., Lundqvist, J., Ahmann, K., Dockter, C., Matyszczak, I., Kurowska, M., Druka, A., Waugh, R., Graner, A., Stein, N., Steuernagel, B., Lundqvist, U., Hansson, M. 2012; 109 (11): 4326-4331

    Abstract

    Time to flowering has an important impact on yield and has been a key trait in the domestication of crop plants and the spread of agriculture. In 1961, the cultivar Mari (mat-a.8) was the very first induced early barley (Hordeum vulgare L.) mutant to be released into commercial production. Mari extended the range of two-row spring barley cultivation as a result of its photoperiod insensitivity. Since its release, Mari or its derivatives have been used extensively across the world to facilitate short-season adaptation and further geographic range extension. By exploiting an extended historical collection of early-flowering mutants of barley, we identified Praematurum-a (Mat-a), the gene responsible for this key adaptive phenotype, as a homolog of the Arabidopsis thaliana circadian clock regulator Early Flowering 3 (Elf3). We characterized 87 induced mat-a mutant lines and identified >20 different mat-a alleles that had clear mutations leading to a defective putative ELF3 protein. Expression analysis of HvElf3 and Gigantea in mutant and wild-type plants demonstrated that mat-a mutations disturb the flowering pathway, leading to the early phenotype. Alleles of Mat-a therefore have important and demonstrated breeding value in barley but probably also in many other day-length-sensitive crop plants, where they may tune adaptation to different geographic regions and climatic conditions, a critical issue in times of global warming.

    View details for DOI 10.1073/pnas.1113009109

    View details for Web of Science ID 000301426700061

    View details for PubMedID 22371569

  • Rigid Core and Flexible Terminus STRUCTURE OF SOLUBILIZED LIGHT-HARVESTING CHLOROPHYLL a/b COMPLEX (LHCII) MEASURED BY EPR JOURNAL OF BIOLOGICAL CHEMISTRY Dockter, C., Mueller, A. H., Dietz, C., Volkov, A., Polyhach, Y., Jeschke, G., Paulsen, H. 2012; 287 (4): 2915-2925

    Abstract

    The structure of the major light-harvesting chlorophyll a/b complex (LHCII) was analyzed by pulsed EPR measurements and compared with the crystal structure. Site-specific spin labeling of the recombinant protein allowed the measurement of distance distributions over several intra- and intermolecular distances in monomeric and trimeric LHCII, yielding information on the protein structure and its local flexibility. A spin label rotamer library based on a molecular dynamics simulation was used to take the local mobility of spin labels into account. The core of LHCII in solution adopts a structure very similar or identical to the one seen in crystallized LHCII trimers with little motional freedom as indicated by narrow distance distributions along and between ? helices. However, distances comprising the lumenal loop domain show broader distance distributions, indicating some mobility of this loop structure. Positions in the hydrophilic N-terminal domain, upstream of the first trans-membrane ? helix, exhibit more and more mobility the closer they are to the N terminus. The nine amino acids at the very N terminus that have not been resolved in any of the crystal structure analyses give rise to very broad and possibly bimodal distance distributions, which may represent two families of preferred conformations.

    View details for DOI 10.1074/jbc.M111.307728

    View details for Web of Science ID 000300292300063

    View details for PubMedID 22147706

  • Methods for the preparation of chlorophyllide a: An intermediate of the chlorophyll biosynthetic pathway ANALYTICAL BIOCHEMISTRY Muller, A. H., Gough, S. P., Bollivar, D. W., Meldal, M., Willows, R. D., Hansson, M. 2011; 419 (2): 271-276

    Abstract

    Chlorophyllide a is a metabolite late in the biosynthesis of chlorophylls and bacteriochlorophylls. Isolation procedures for chlorophyllide a from Rhodobacter capsulatus CB1200 and barley (Hordeum vulgare L.) are described and compared. R. capsulatus CB1200 is a double mutant in the bacteriochlorophyllide a biosynthetic pathway, and chlorophyllide a is excreted by the cells when grown in Tween 80-containing liquid medium. It was purified by liquid or solid phase extraction, yielding 7 mg of chlorophyllide a from 1 L of culture. In a second approach, intrinsic chlorophyllase activity was used to dephytylate chlorophyll in an acetonic preparation of leaves of wild-type or chlorophyll b-deficient barley. Purification was achieved by liquid phase extraction, yielding 14 ?g of chlorophyllide a per gram of barley leaves. Chlorophyllide a was identified by thin layer chromatography, absorption spectroscopy, and mass spectrometry.

    View details for DOI 10.1016/j.ab.2011.08.028

    View details for Web of Science ID 000296119400029

    View details for PubMedID 21925479

  • The Barley Magnesium Chelatase 150-kD Subunit Is Not an Abscisic Acid Receptor PLANT PHYSIOLOGY Muller, A. H., Hansson, M. 2009; 150 (1): 157-166

    Abstract

    Magnesium chelatase is the first unique enzyme of the chlorophyll biosynthetic pathway. It is composed of three gene products of which the largest is 150 kD. This protein was recently identified as an abscisic acid receptor in Arabidopsis (Arabidopsis thaliana). We have evaluated whether the barley (Hordeum vulgare) magnesium chelatase large subunit, XanF, could be a receptor for the phytohormone. The study involved analysis of recombinant magnesium chelatase protein as well as several induced chlorophyll-deficient magnesium chelatase mutants with defects identified at the gene and protein levels. Abscisic acid had no effect on magnesium chelatase activity and binding to the barley 150-kD protein could not be shown. Magnesium chelatase mutants showed a wild-type response in respect to postgermination growth and stomatal aperture. Our results question the function of the large magnesium chelatase subunit as an abscisic acid receptor.

    View details for DOI 10.1104/pp.109.135277

    View details for Web of Science ID 000265661700014

    View details for PubMedID 19176716

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