title: Expression of S-adenosylmethionine Hydrolase in Tissues Synthesizing Secondary Cell Walls Alters Specific Methylated Cell Wall Fractions and Improves Biomass Digestibility.
abstract: Plant biomass is a large source of fermentable sugars for the synthesis of bioproducts using engineered microbes. These sugars are stored as cell wall polymers, mainly cellulose and hemicellulose, and are embedded with lignin, which makes their enzymatic hydrolysis challenging. One of the strategies to reduce cell wall recalcitrance is the modification of lignin content and composition. Lignin is a phenolic polymer of methylated aromatic alcohols and its synthesis in tissues developing secondary cell walls is a significant sink for the consumption of the methyl donor S-adenosylmethionine (AdoMet). In this study, we demonstrate in Arabidopsis stems that targeted expression of AdoMet hydrolase (AdoMetase, E.C. 3.3.1.2) in secondary cell wall synthesizing tissues reduces the AdoMet pool and impacts lignin content and composition. In particular, both NMR analysis and pyrolysis gas chromatography mass spectrometry of lignin in engineered biomass showed relative enrichment of non-methylated p-hydroxycinnamyl (H) units and a reduction of dimethylated syringyl (S) units. This indicates a lower degree of methylation compared to that in wild-type lignin. Quantification of cell wall-bound hydroxycinnamates revealed a reduction of ferulate in AdoMetase transgenic lines. Biomass from transgenic lines, in contrast to that in control plants, exhibits an enrichment of glucose content and a reduction in the degree of hemicellulose glucuronoxylan methylation. We also show that these modifications resulted in a reduction of cell wall recalcitrance, because sugar yield generated by enzymatic biomass saccharification was greater than that of wild-type plants. Considering that transgenic plants show no important diminution of biomass yields, and that heterologous expression of AdoMetase protein can be spatiotemporally optimized, this novel approach provides a valuable option for the improvement of lignocellulosic biomass feedstock.
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Aymerick
authors.initials: A
authors.lastname: Eudes
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA; Department of Bioengineering, University of California, Berkeley, CA, USA; Department of Chemical & Biomolecular Engineering, University of California, Berkeley, CA, USA.
authors.forename: Nanxia
authors.initials: N
authors.lastname: Zhao
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Department of Bioengineering, University of California, Berkeley, CA, USA; Department of Chemical & Biomolecular Engineering, University of California, Berkeley, CA, USA; Department of Chemical Engineering, Conn Center for Renewable Energy, University of Louisville, Louisville, KY, USA.
authors.forename: Noppadon
authors.initials: N
authors.lastname: Sathitsuksanoh
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Edward E K
authors.initials: EE
authors.lastname: Baidoo
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Jeemeng
authors.initials: J
authors.lastname: Lao
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: George
authors.initials: G
authors.lastname: Wang
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA; Department of Bioengineering, University of California, Berkeley, CA, USA; Department of Chemical & Biomolecular Engineering, University of California, Berkeley, CA, USA.
authors.forename: Sasha
authors.initials: S
authors.lastname: Yogiswara
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Taek Soon
authors.initials: TS
authors.lastname: Lee
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Sandia National Laboratory, Livermore, CA, USA.
authors.forename: Seema
authors.initials: S
authors.lastname: Singh
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Jenny C
authors.initials: JC
authors.lastname: Mortimer
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA; Department of Bioengineering, University of California, Berkeley, CA, USA; Department of Chemical & Biomolecular Engineering, University of California, Berkeley, CA, USA.
authors.forename: Jay D
authors.initials: JD
authors.lastname: Keasling
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA; Sandia National Laboratory, Livermore, CA, USA.
authors.forename: Blake A
authors.initials: BA
authors.lastname: Simmons
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA; Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA; Université Claude Bernard Lyon 1, INSA de Lyon, CNRS, UMR5240, Microbiologie, Adaptation et Pathogénie, Villeurbanne, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Loqué
keywords: AdoMetase; S-adenosylmethionine; Yang cycle; cell wall; glucuronoxylan; lignin; saccharification