title: Tricin, a flavonoid monomer in monocot lignification.
abstract: Tricin was recently discovered in lignin preparations from wheat (Triticum aestivum) straw and subsequently in all monocot samples examined. To provide proof that tricin is involved in lignification and establish the mechanism by which it incorporates into the lignin polymer, the 4'-O-β-coupling products of tricin with the monolignols (p-coumaryl, coniferyl, and sinapyl alcohols) were synthesized along with the trimer that would result from its 4'-O-β-coupling with sinapyl alcohol and then coniferyl alcohol. Tricin was also found to cross couple with monolignols to form tricin-(4'-O-β)-linked dimers in biomimetic oxidations using peroxidase/hydrogen peroxide or silver (I) oxide. Nuclear magnetic resonance characterization of gel permeation chromatography-fractionated acetylated maize (Zea mays) lignin revealed that the tricin moieties are found in even the highest molecular weight fractions, ether linked to lignin units, demonstrating that tricin is indeed incorporated into the lignin polymer. These findings suggest that tricin is fully compatible with lignification reactions, is an authentic lignin monomer, and, because it can only start a lignin chain, functions as a nucleation site for lignification in monocots. This initiation role helps resolve a long-standing dilemma that monocot lignin chains do not appear to be initiated by monolignol homodehydrodimerization as they are in dicots that have similar syringyl-guaiacyl compositions. The term flavonolignin is recommended for the racemic oligomers and polymers of monolignols that start from tricin (or incorporate other flavonoids) in the cell wall, in analogy with the existing term flavonolignan that is used for the low-molecular mass compounds composed of flavonoid and lignan moieties.
authors: Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute (W.L., F.L., M.R., Y.Z., J.Re., U.I.Z., J.Ra.), Department of Biological System Engineering (W.L., J.Ra.), and Department of Biochemistry (F.L., M.R., J.Ra.), University of Wisconsin, Madison, Wisconsin 53726;United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726 (S.A.R.); andDepartment of Plant Systems Biology, Vlaams Instituut voor Biotechnologie, andDepartment of Plant Biotechnology and Bioinformatics, Ghent University, B-9052 Ghent, Belgium (K.M., W.B.).
authors: Wu
authors: W
authors: Lan
authors: Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute (W.L., F.L., M.R., Y.Z., J.Re., U.I.Z., J.Ra.), Department of Biological System Engineering (W.L., J.Ra.), and Department of Biochemistry (F.L., M.R., J.Ra.), University of Wisconsin, Madison, Wisconsin 53726;United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726 (S.A.R.); andDepartment of Plant Systems Biology, Vlaams Instituut voor Biotechnologie, andDepartment of Plant Biotechnology and Bioinformatics, Ghent University, B-9052 Ghent, Belgium (K.M., W.B.) fachuanglu@wisc.edu jralph@wisc.edu.
authors: Fachuang
authors: F
authors: Lu
authors: Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute (W.L., F.L., M.R., Y.Z., J.Re., U.I.Z., J.Ra.), Department of Biological System Engineering (W.L., J.Ra.), and Department of Biochemistry (F.L., M.R., J.Ra.), University of Wisconsin, Madison, Wisconsin 53726;United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726 (S.A.R.); andDepartment of Plant Systems Biology, Vlaams Instituut voor Biotechnologie, andDepartment of Plant Biotechnology and Bioinformatics, Ghent University, B-9052 Ghent, Belgium (K.M., W.B.).
authors: Matthew
authors: M
authors: Regner
authors: Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute (W.L., F.L., M.R., Y.Z., J.Re., U.I.Z., J.Ra.), Department of Biological System Engineering (W.L., J.Ra.), and Department of Biochemistry (F.L., M.R., J.Ra.), University of Wisconsin, Madison, Wisconsin 53726;United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726 (S.A.R.); andDepartment of Plant Systems Biology, Vlaams Instituut voor Biotechnologie, andDepartment of Plant Biotechnology and Bioinformatics, Ghent University, B-9052 Ghent, Belgium (K.M., W.B.).
authors: Yimin
authors: Y
authors: Zhu
authors: Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute (W.L., F.L., M.R., Y.Z., J.Re., U.I.Z., J.Ra.), Department of Biological System Engineering (W.L., J.Ra.), and Department of Biochemistry (F.L., M.R., J.Ra.), University of Wisconsin, Madison, Wisconsin 53726;United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726 (S.A.R.); andDepartment of Plant Systems Biology, Vlaams Instituut voor Biotechnologie, andDepartment of Plant Biotechnology and Bioinformatics, Ghent University, B-9052 Ghent, Belgium (K.M., W.B.).
authors: Jorge
authors: J
authors: Rencoret
authors: Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute (W.L., F.L., M.R., Y.Z., J.Re., U.I.Z., J.Ra.), Department of Biological System Engineering (W.L., J.Ra.), and Department of Biochemistry (F.L., M.R., J.Ra.), University of Wisconsin, Madison, Wisconsin 53726;United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726 (S.A.R.); andDepartment of Plant Systems Biology, Vlaams Instituut voor Biotechnologie, andDepartment of Plant Biotechnology and Bioinformatics, Ghent University, B-9052 Ghent, Belgium (K.M., W.B.).
authors: Sally A
authors: SA
authors: Ralph
authors: Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute (W.L., F.L., M.R., Y.Z., J.Re., U.I.Z., J.Ra.), Department of Biological System Engineering (W.L., J.Ra.), and Department of Biochemistry (F.L., M.R., J.Ra.), University of Wisconsin, Madison, Wisconsin 53726;United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726 (S.A.R.); andDepartment of Plant Systems Biology, Vlaams Instituut voor Biotechnologie, andDepartment of Plant Biotechnology and Bioinformatics, Ghent University, B-9052 Ghent, Belgium (K.M., W.B.).
authors: Uzma I
authors: UI
authors: Zakai
authors: Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute (W.L., F.L., M.R., Y.Z., J.Re., U.I.Z., J.Ra.), Department of Biological System Engineering (W.L., J.Ra.), and Department of Biochemistry (F.L., M.R., J.Ra.), University of Wisconsin, Madison, Wisconsin 53726;United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726 (S.A.R.); andDepartment of Plant Systems Biology, Vlaams Instituut voor Biotechnologie, andDepartment of Plant Biotechnology and Bioinformatics, Ghent University, B-9052 Ghent, Belgium (K.M., W.B.).
authors: Kris
authors: K
authors: Morreel
authors: Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute (W.L., F.L., M.R., Y.Z., J.Re., U.I.Z., J.Ra.), Department of Biological System Engineering (W.L., J.Ra.), and Department of Biochemistry (F.L., M.R., J.Ra.), University of Wisconsin, Madison, Wisconsin 53726;United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726 (S.A.R.); andDepartment of Plant Systems Biology, Vlaams Instituut voor Biotechnologie, andDepartment of Plant Biotechnology and Bioinformatics, Ghent University, B-9052 Ghent, Belgium (K.M., W.B.).
authors: Wout
authors: W
authors: Boerjan
authors: Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute (W.L., F.L., M.R., Y.Z., J.Re., U.I.Z., J.Ra.), Department of Biological System Engineering (W.L., J.Ra.), and Department of Biochemistry (F.L., M.R., J.Ra.), University of Wisconsin, Madison, Wisconsin 53726;United States Forest Service, Forest Products Laboratory, Madison, Wisconsin 53726 (S.A.R.); andDepartment of Plant Systems Biology, Vlaams Instituut voor Biotechnologie, andDepartment of Plant Biotechnology and Bioinformatics, Ghent University, B-9052 Ghent, Belgium (K.M., W.B.) fachuanglu@wisc.edu jralph@wisc.edu.
authors: John
authors: J
authors: Ralph
mesh_terms: D000107:Acetylation; D053898:Biosynthetic Pathways; D002473:Cell Wall / Q000378:metabolism; D005419:Flavonoids / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D008031:Lignin / Q000737:chemistry / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008970:Molecular Weight; D010636:Phenols / Q000737:chemistry / Q000378:metabolism; D011108:Polymers / Q000378:metabolism; D014908:Triticum / Q000737:chemistry* / Q000378:metabolism; D003313:Zea mays / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005419:Flavonoids; D010636:Phenols; D011108:Polymers; D008031:Lignin; C017769:tricin; C010559:coniferyl alcohol