title: CCoAOMT suppression modifies lignin composition in Pinus radiata.
abstract: A cDNA clone encoding the lignin-related enzyme caffeoyl CoA 3-O-methyltransferase (CCoAOMT) was isolated from a Pinus radiata cDNA library derived from differentiating xylem. Suppression of PrCCoAOMT expression in P. radiata tracheary element cultures affected lignin content and composition, resulting in a lignin polymer containing p-hydroxyphenyl (H), catechyl (C) and guaiacyl (G) units. Acetyl bromide-soluble lignin assays revealed reductions in lignin content of up to 20% in PrCCoAOMT-deficient transgenic lines. Pyrolysis-GC/MS and 2D-NMR studies demonstrated that these reductions were due to depletion of G-type lignin. Correspondingly, the proportion of H-type lignin in PrCCoAOMT-deficient transgenic lines increased, resulting in up to a 10-fold increase in the H/G ratio relative to untransformed controls. 2D-NMR spectra revealed that PrCCoAOMT suppression resulted in formation of benzodioxanes in the lignin polymer. This suggested that phenylpropanoids with an ortho-diphenyl structure such as caffeyl alcohol are involved in lignin polymerization. To test this hypothesis, synthetic lignins containing methyl caffeate or caffeyl alcohol were generated and analyzed by 2D-NMR. Comparison of the 2D-NMR spectra from PrCCoAOMT-RNAi lines and synthetic lignins identified caffeyl alcohol as the new lignin constituent in PrCCoAOMT-deficient lines. The incorporation of caffeyl alcohol into lignin created a polymer containing catechyl units, a lignin type that has not been previously identified in recombinant lignin studies. This finding is consistent with the theory that lignin polymerization is based on a radical coupling process that is determined solely by chemical processes.
authors.affiliation: Scion, Private Bag 3020, Rotorua, New Zealand Department of Biochemistry, University of Wisconsin, Madison, WI, USA. armin.wagner@scionresearch.com
authors.forename: Armin
authors.initials: A
authors.lastname: Wagner
authors.forename: Yuki
authors.initials: Y
authors.lastname: Tobimatsu
authors.forename: Lorelle
authors.initials: L
authors.lastname: Phillips
authors.forename: Heather
authors.initials: H
authors.lastname: Flint
authors.forename: Kirk
authors.initials: K
authors.lastname: Torr
authors.forename: Lloyd
authors.initials: L
authors.lastname: Donaldson
authors.forename: Lana
authors.initials: L
authors.lastname: Pears
authors.forename: John
authors.initials: J
authors.lastname: Ralph
mesh_terms: D001483:Base Sequence; D002109:Caffeic Acids / Q000378:metabolism; D018929:Cell Culture Techniques; D015536:Down-Regulation; D015723:Gene Library; D008031:Lignin / Q000737:chemistry / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008780:Methyltransferases / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D028223:Pinus / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D058105:Polymerization; D020005:Propanols / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D017422:Sequence Analysis, DNA; D052584:Xylem / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*
chemical_list: D002109:Caffeic Acids; D020005:Propanols; D018749:RNA, Plant; C042405:methyl caffeate; D008031:Lignin; D008780:Methyltransferases; C059825:caffeoyl-CoA O-methyltransferase