title: Metabolite profiling reveals a role for atypical cinnamyl alcohol dehydrogenase CAD1 in the synthesis of coniferyl alcohol in tobacco xylem.
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.
authors.affiliation: UMR UPS/CNRS 5546 "Surfaces Cellulaires et Signalisation chez les Végétaux", Pôle de Biotechnologie Végétale, 24 chemin de Borderouge, BP 42617, F-31326, Castanet, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Damiani
authors.forename: Kris
authors.initials: K
authors.lastname: Morreel
authors.forename: Saïda
authors.initials: S
authors.lastname: Danoun
authors.forename: Geert
authors.initials: G
authors.lastname: Goeminne
authors.forename: Nabila
authors.initials: N
authors.lastname: Yahiaoui
authors.forename: Christiane
authors.initials: C
authors.lastname: Marque
authors.forename: Joachim
authors.initials: J
authors.lastname: Kopka
authors.forename: Eric
authors.initials: E
authors.lastname: Messens
authors.forename: Deborah
authors.initials: D
authors.lastname: Goffner
authors.forename: Wout
authors.initials: W
authors.lastname: Boerjan
authors.forename: Alain-Michel
authors.initials: AM
authors.lastname: Boudet
authors.forename: Soizic
authors.initials: S
authors.lastname: Rochange
mesh_terms: D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008031:Lignin / Q000096:biosynthesis; D008956:Models, Chemical; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D014026:Nicotiana / Q000166:cytology* / Q000201:enzymology* / Q000235:genetics
chemical_list: D010636:Phenols; D010940:Plant Proteins; D008031:Lignin; C010559:coniferyl alcohol; D000429:Alcohol Oxidoreductases; C018656:cinnamyl alcohol dehydrogenase