title: Biosynthesis and incorporation of side-chain-truncated lignin monomers to reduce lignin polymerization and enhance saccharification.
abstract: Lignocellulosic biomass is utilized as a renewable feedstock in various agro-industrial activities. Lignin is an aromatic, hydrophobic and mildly branched polymer integrally associated with polysaccharides within the biomass, which negatively affects their extraction and hydrolysis during industrial processing. Engineering the monomer composition of lignins offers an attractive option towards new lignins with reduced recalcitrance. The presented work describes a new strategy developed in Arabidopsis for the overproduction of rare lignin monomers to reduce lignin polymerization degree (DP). Biosynthesis of these 'DP reducers' is achieved by expressing a bacterial hydroxycinnamoyl-CoA hydratase-lyase (HCHL) in lignifying tissues of Arabidopsis inflorescence stems. HCHL cleaves the propanoid side-chain of hydroxycinnamoyl-CoA lignin precursors to produce the corresponding hydroxybenzaldehydes so that plant stems expressing HCHL accumulate in their cell wall higher amounts of hydroxybenzaldehyde and hydroxybenzoate derivatives. Engineered plants with intermediate HCHL activity levels show no reduction in total lignin, sugar content or biomass yield compared with wild-type plants. However, cell wall characterization of extract-free stems by thioacidolysis and by 2D-NMR revealed an increased amount of unusual C₆C₁ lignin monomers most likely linked with lignin as end-groups. Moreover the analysis of lignin isolated from these plants using size-exclusion chromatography revealed a reduced molecular weight. Furthermore, these engineered lines show saccharification improvement of pretreated stem cell walls. Therefore, we conclude that enhancing the biosynthesis and incorporation of C₆C₁ monomers ('DP reducers') into lignin polymers represents a promising strategy to reduce lignin DP and to decrease cell wall recalcitrance to enzymatic hydrolysis.
authors.affiliation: Joint BioEnergy Institute, EmeryStation East, Emeryville, CA, USA.
authors.forename: Aymerick
authors.initials: A
authors.lastname: Eudes
authors.forename: Anthe
authors.initials: A
authors.lastname: George
authors.forename: Purba
authors.initials: P
authors.lastname: Mukerjee
authors.forename: Jin S
authors.initials: JS
authors.lastname: Kim
authors.forename: Brigitte
authors.initials: B
authors.lastname: Pollet
authors.forename: Peter I
authors.initials: PI
authors.lastname: Benke
authors.forename: Fan
authors.initials: F
authors.lastname: Yang
authors.forename: Prajakta
authors.initials: P
authors.lastname: Mitra
authors.forename: Lan
authors.initials: L
authors.lastname: Sun
authors.forename: Ozgül P
authors.initials: OP
authors.lastname: Cetinkol
authors.forename: Salem
authors.initials: S
authors.lastname: Chabout
authors.forename: Grégory
authors.initials: G
authors.lastname: Mouille
authors.forename: Ludivine
authors.initials: L
authors.lastname: Soubigou-Taconnat
authors.forename: Sandrine
authors.initials: S
authors.lastname: Balzergue
authors.forename: Seema
authors.initials: S
authors.lastname: Singh
authors.forename: Bradley M
authors.initials: BM
authors.lastname: Holmes
authors.forename: Aindrila
authors.initials: A
authors.lastname: Mukhopadhyay
authors.forename: Jay D
authors.initials: JD
authors.lastname: Keasling
authors.forename: Blake A
authors.initials: BA
authors.lastname: Simmons
authors.forename: Catherine
authors.initials: C
authors.lastname: Lapierre
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.forename: Dominique
authors.initials: D
authors.lastname: Loqué
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D018533:Biomass; D002473:Cell Wall / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D006836:Hydro-Lyases / Q000235:genetics / Q000378:metabolism*; D008031:Lignin / Q000096:biosynthesis*; D018547:Plant Stems / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D058105:Polymerization; D011401:Promoter Regions, Genetic; D014170:Transformation, Genetic
chemical_list: D008031:Lignin; C119166:4-hydroxycinnamoyl-CoA hydratase-lyase; D006836:Hydro-Lyases