title: Hydroxycinnamate conjugates as potential monolignol replacements: in vitro lignification and cell wall studies with rosmarinic acid.
abstract: The plasticity of lignin biosynthesis should permit the inclusion of new compatible phenolic monomers, such as rosmarinic acid (RA) and analogous catechol derivatives, into cell-wall lignins that are consequently less recalcitrant to biomass processing. In vitro lignin polymerization experiments revealed that RA readily underwent peroxidase-catalyzed copolymerization with monolignols and lignin oligomers to form polymers with new benzodioxane inter-unit linkages. Incorporation of RA permitted extensive depolymerization of synthetic lignins by mild alkaline hydrolysis, presumably by cleavage of ester intra-unit linkages within RA. Copolymerization of RA with monolignols into maize cell walls by in situ peroxidases significantly enhanced alkaline lignin extractability and promoted subsequent cell wall saccharification by fungal enzymes. Incorporating RA also improved cell wall saccharification by fungal enzymes and by rumen microflora even without alkaline pretreatments, possibly by modulating lignin hydrophobicity and/or limiting cell wall cross-linking. Consequently, we anticipate that bioengineering approaches for partial monolignol substitution with RA and analogous plant hydroxycinnamates would permit more efficient utilization of plant fiber for biofuels or livestock production.
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, Enzyme Institute, Madison, Wisconsin 53726, USA. tobimatsu@wisc.edu
authors.forename: Yuki
authors.initials: Y
authors.lastname: Tobimatsu
authors.forename: Sasikumar
authors.initials: S
authors.lastname: Elumalai
authors.forename: John H
authors.initials: JH
authors.lastname: Grabber
authors.forename: Christy L
authors.initials: CL
authors.lastname: Davidson
authors.forename: Xuejun
authors.initials: X
authors.lastname: Pan
authors.forename: John
authors.initials: J
authors.lastname: Ralph
mesh_terms: D000818:Animals; D001419:Bacteria / Q000378:metabolism; D055162:Biocatalysis; D032701:Biomimetics; D002473:Cell Wall / Q000378:metabolism* / Q000382:microbiology; D002934:Cinnamates / Q000378:metabolism*; D003373:Coumaric Acids / Q000378:metabolism*; D053630:Depsides / Q000378:metabolism*; D005285:Fermentation; D006735:Horseradish Peroxidase / Q000378:metabolism; D006868:Hydrolysis; D008031:Lignin / Q000378:metabolism*; D058105:Polymerization; D012417:Rumen / Q000382:microbiology; D003313:Zea mays / Q000166:cytology; D000097123:Rosmarinic Acid
chemical_list: D002934:Cinnamates; D003373:Coumaric Acids; D053630:Depsides; D006735:Horseradish Peroxidase; D008031:Lignin; D000097123:Rosmarinic Acid