title: Engineering traditional monolignols out of lignin by concomitant up-regulation of F5H1 and down-regulation of COMT in Arabidopsis.
abstract: Lignin engineering is a promising strategy to optimize lignocellulosic plant biomass for use as a renewable feedstock for agro-industrial applications. Current efforts focus on engineering lignin with monomers that are not normally incorporated into wild-type lignins. Here we describe an Arabidopsis line in which the lignin is derived to a major extent from a non-traditional monomer. The combination of mutation in the gene encoding caffeic acid O-methyltransferase (comt) with over-expression of ferulate 5-hydroxylase under the control of the cinnamate 4-hydroxylase promoter (C4H:F5H1) resulted in plants with a unique lignin comprising almost 92% benzodioxane units. In addition to biosynthesis of this particular lignin, the comt C4H:F5H1 plants revealed massive shifts in phenolic metabolism compared to the wild type. The structures of 38 metabolites that accumulated in comt C4H:F51 plants were resolved by mass spectral analyses, and were shown to derive from 5-hydroxy-substituted phenylpropanoids. These metabolites probably originate from passive metabolism via existing biochemical routes normally used for 5-methoxylated and 5-unsubstituted phenylpropanoids and from active detoxification by hexosylation. Transcripts of the phenylpropanoid biosynthesis pathway were highly up-regulated in comt C4H:F5H1 plants, indicating feedback regulation within the pathway. To investigate the role of flavonoids in the abnormal growth of comt C4H:F5H1 plants, a mutation in a gene encoding chalcone synthase (chs) was crossed in. The resulting comt C4H:F5H1 chs plants showed partial restoration of growth. However, a causal connection between flavonoid deficiency and this restoration of growth was not demonstrated; instead, genetic interactions between phenylpropanoid and flavonoid biosynthesis could explain the partial restoration. These genetic interactions must be taken into account in future cell-wall engineering strategies.
authors.affiliation: Department of Plant Systems Biology, VIB, 9052 Gent, Belgium.
authors.forename: Ruben
authors.initials: R
authors.lastname: Vanholme
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.forename: Takuya
authors.initials: T
authors.lastname: Akiyama
authors.forename: Fachuang
authors.initials: F
authors.lastname: Lu
authors.forename: Jorge Rencoret
authors.initials: JR
authors.lastname: Pazo
authors.forename: Hoon
authors.initials: H
authors.lastname: Kim
authors.forename: Jørgen Holst
authors.initials: JH
authors.lastname: Christensen
authors.forename: Brecht
authors.initials: B
authors.lastname: Van Reusel
authors.forename: Véronique
authors.initials: V
authors.lastname: Storme
authors.forename: Riet
authors.initials: R
authors.lastname: De Rycke
authors.forename: Antje
authors.initials: A
authors.lastname: Rohde
authors.forename: Kris
authors.initials: K
authors.lastname: Morreel
authors.forename: Wout
authors.initials: W
authors.lastname: Boerjan
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D018506:Gene Expression Regulation, Plant; D008031:Lignin / Q000096:biosynthesis*; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010636:Phenols / Q000378:metabolism; D010641:Phenotype; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D011401:Promoter Regions, Genetic; D015854:Up-Regulation
chemical_list: D029681:Arabidopsis Proteins; D010636:Phenols; D008031:Lignin; D003577:Cytochrome P-450 Enzyme System; C097486:CYP84A1 protein, Arabidopsis; D008780:Methyltransferases; C019608:caffeate O-methyltransferase