Metabolite Profiling Reveals a Role for Atypical Cinnamyl Alcohol Dehydrogenase CAD1 in the Synthesis of Coniferyl Alcohol in Tobacco Xylem |
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Authors: | Isabelle Damiani Kris Morreel Saïda Danoun Geert Goeminne Nabila Yahiaoui Christiane Marque Joachim Kopka Eric Messens Deborah Goffner Wout Boerjan Alain-Michel Boudet Soizic Rochange |
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Institution: | 1. UMR UPS/CNRS 5546 “Surfaces Cellulaires et Signalisation chez les Végétaux”, P?le de Biotechnologie Végétale, 24 chemin de Borderouge, BP 42617, F-31326, Castanet, France 2. Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology (VIB),, Ghent University, B-9052, Ghent, Belgium 4. Institute of Plant Biology, University of Zürich, 107 8008, Zollikerstrasse, Zürich, Switzerland 3. Max-Planck Institute of Molecular Plant Physiology, Am Muehlenberg 1, D-14476, Golm-Potsdam, Germany
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Abstract: | In angiosperms, lignin is built from two main monomers, coniferyl and sinapyl alcohol, which are incorporated respectively
as G and S units in the polymer. The last step of their synthesis has so far been considered to be performed by a family of
dimeric cinnamyl alcohol dehydrogenases (CAD2). However, previous studies on Eucalyptus gunnii xylem showed the presence of an additional, structurally unrelated, monomeric CAD form named CAD1. This form reduces coniferaldehyde
to coniferyl alcohol, but is inactive on sinapaldehyde. In this paper, we report the functional characterization of CAD1 in
tobacco (Nicotiana tabacum L.). Transgenic tobacco plants with reduced CAD1 expression were obtained through an RNAi strategy. These plants displayed normal growth and development, and detailed biochemical
studies were needed to reveal a role for CAD1. Lignin analyses showed that CAD1 down-regulation does not affect Klason lignin content, and has a moderate impact on G unit content of the non-condensed lignin
fraction. However, comparative metabolic profiling of the methanol-soluble phenolic fraction from basal xylem revealed significant
differences between CAD1 down-regulated and wild-type plants. Eight compounds were less abundant in CAD1 down-regulated lines, five of which were identified as dimers or trimers of monolignols, each containing at least one moiety
derived from coniferyl alcohol. In addition, 3-trans-caffeoyl quinic acid accumulated in the transgenic plants. Together, our results support a significant contribution of CAD1
to the synthesis of coniferyl alcohol in planta, along with the previously characterized CAD2 enzymes.
Sequences of NtCAD1-1 and NtCAD1-7 were deposited in GenBank under accession numbers AY911854 and AY911855, respectively. |
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Keywords: | cinnamyl alcohol dehydrogenase coniferyl alcohol lignin xylem |
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