title: Expression of a bacterial 3-dehydroshikimate dehydratase reduces lignin content and improves biomass saccharification efficiency.
abstract: Lignin confers recalcitrance to plant biomass used as feedstocks in agro-processing industries or as source of renewable sugars for the production of bioproducts. The metabolic steps for the synthesis of lignin building blocks belong to the shikimate and phenylpropanoid pathways. Genetic engineering efforts to reduce lignin content typically employ gene knockout or gene silencing techniques to constitutively repress one of these metabolic pathways. Recently, new strategies have emerged offering better spatiotemporal control of lignin deposition, including the expression of enzymes that interfere with the normal process for cell wall lignification. In this study, we report that expression of a 3-dehydroshikimate dehydratase (QsuB from Corynebacterium glutamicum) reduces lignin deposition in Arabidopsis cell walls. QsuB was targeted to the plastids to convert 3-dehydroshikimate - an intermediate of the shikimate pathway - into protocatechuate. Compared to wild-type plants, lines expressing QsuB contain higher amounts of protocatechuate, p-coumarate, p-coumaraldehyde and p-coumaryl alcohol, and lower amounts of coniferaldehyde, coniferyl alcohol, sinapaldehyde and sinapyl alcohol. 2D-NMR spectroscopy and pyrolysis-gas chromatography/mass spectrometry (pyro-GC/MS) reveal an increase of p-hydroxyphenyl units and a reduction of guaiacyl units in the lignin of QsuB lines. Size-exclusion chromatography indicates a lower degree of lignin polymerization in the transgenic lines. Therefore, our data show that the expression of QsuB primarily affects the lignin biosynthetic pathway. Finally, biomass from these lines exhibits more than a twofold improvement in saccharification efficiency. We conclude that the expression of QsuB in plants, in combination with specific promoters, is a promising gain-of-function strategy for spatiotemporal reduction of lignin in plant biomass.
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA.|Physical Biosciences 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.|Sandia National Laboratory, Livermore, CA, USA.
authors.forename: Noppadon
authors.initials: N
authors.lastname: Sathitsuksanoh
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA.|Physical Biosciences 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.|Sandia National Laboratory, Livermore, CA, USA.
authors.forename: Anthe
authors.initials: A
authors.lastname: George
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA.|Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Liang
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA.|Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Fan
authors.initials: F
authors.lastname: Yang
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.|Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.|Department of Bioengineering, 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.|Sandia National Laboratory, Livermore, CA, USA.
authors.forename: Blake A
authors.initials: BA
authors.lastname: Simmons
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA, USA.|Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Dominique
authors.initials: D
authors.lastname: Loqué
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D018533:Biomass; D050260:Carbohydrate Metabolism; D002473:Cell Wall / Q000378:metabolism; D048230:Corynebacterium glutamicum / Q000201:enzymology; D005818:Genetic Engineering / Q000379:methods; D006836:Hydro-Lyases / Q000378:metabolism*; D008031:Lignin / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D053858:Metabolic Networks and Pathways
chemical_list: D008031:Lignin; C044921:3-dehydroshikimate dehydratase; D006836:Hydro-Lyases
keywords: QsuB; bioenergy; cell wall; lignin; lignin polymerization degree; saccharification