Engineering plant cell walls: tuning lignin monomer composition for deconstructable biofuel feedstocks or resilient biomaterials

Abstract

Advances in genetic manipulation of the biopolymers that compose plant cell walls will facilitate more efficient production of biofuels and chemicals from biomass and lead to specialized biomaterials with tailored properties. Here we investigate several genetic variants of Arabidopsis: the wild type, which makes a lignin polymer of primarily guaiacyl (G) and syringyl (S) monomeric units, the fah1 mutant, which makes lignin from almost exclusively G subunits, and a ferulate 5-hydroxylase (F5H) overexpressing line (C4H: F5H) that makes lignin from S subunits. We employ multiscale, multimodal imaging techniques that reveal the biomass of the C4H:F5H transgenic to be more susceptible to deconstruction by maleic acid treatment than the other variants. Enzymatic saccharification assays of the treated materials show that C4H: F5H transgenic tissue is significantly more digestible than the wild type, while the fah1 mutant is clearly the least digestible of these materials. Finally, we show by contact resonance force microscopy, an atomic force microscopy technique, that F5H overexpression in C4H:F5H transgenic plants significantly reduces the stiffness of the cell walls in the region of the compound middle lamella relative to wild type and fah1. † Electronic supplementary information (ESI) available. See

Manipulation of Guaiacyl and Syringyl Monomer Biosynthesis in an Arabidopsis Cinnamyl Alcohol Dehydrogenase Mutant Results in Atypical Lignin Biosynthesis and Modified Cell Wall Structure

“…Reduction in lignin content is known to improve sugar release from biomass upon treatment with cocktails of polysaccharide hydrolases (Studer et al, 2011), and similar beneficial effects have recently been reported to arise from modifications to lignin composition (Li et al, 2010b;Mansfield et al, 2012b;Ciesielski et al, 2014). We observed that of the four variants examined with low lignin content, cadc cadd and fah1 cadc cadd have the highest enzymatic cellulosic conversion for nonpretreated Arabidopsis inflorescence tissue.…”

“…On the one hand, several plants with disruptions in lignin content exhibit an increase in cell wall digestibility, although the reduced lignin has been correlated with decreased yield (Bonawitz and Chapple, 2013). On the other hand, plants with perturbations that affect lignin composition show improvements in cell wall degradability; however, this increase is sometimes only detectable after pretreatment (Li et al, 2010b;Ciesielski et al, 2014). Lignin composition is plastic and several genetic manipulations have generated plants with nearly homogeneous lignin subunit profiles or lignins derived from noncanonical monomers.…”

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis

“…Theo verexpression of F5H with apowerful lignin promoter (entry 27) leads to al ignin almost exclusively composed of S-units,w hereas downregulation or deficiencies in F5H (entry 28) results in ap redominance of G-units. [117] However,i nb oth cases in Arabidopsis,adecrease in plant stiffness,c aused by the lack of secondary plant wall structure in the interfascicular and Table 2: Summary of reported genetic modificationswithin the phenylpropanoid pathway and their effects on saccharification yield, total lignin content, lignin composition/structure (and/or the effect on metabolites) and plant phenotype;TG(transgenic), M(mutation), ND (not determined).…”

“…[117] Tw oc lasses of O-methyltransferases,t he so-called CCoAOMT and COMT enzymes (Scheme 1), are involved in producing the 3-and 5-methoxyl groups on Ga nd S monomers.5 -Hydroxyconiferaldehyde,w hen 5-O-methylation is deficient, reduces to 5-hydroxyconiferyl alcohol that is then integrally incorporated into lignins in COMT-deficient plants (entries 23 and 24). Ther esulting 5-hydroxyguaiacyl units react by typical 4-O-b-coupling with any of the hydroxycinnamyl alcohol monomers (the prototypical monolignols or further 5-hydroxyconiferyl alcohol), but the internal trapping of the intermediate quinone methide product by the novel 5-OH results in the formation of benzodioxane structures in the polymer.…”

Cell Wall Engineering by Heterologous Expression of Cell Wall-Degrading Enzymes for Better Conversion of Lignocellulosic Biomass into Biofuels

“…Since lignin is essential to support the plant and transport water and nutrients from the roots toward the leaves, large reductions in lignin content result in undesired phenotypes such as dwarfism [136]. Nevertheless, rather than reducing lignin content, changing the structure of the lignin polymer might be another elegant way in order to diminish cell wall recalcitrance [137,138]. Lignin enriched in S-units is more easily removed and more accessible to hydrolytic enzymes, and Arabidopsis plants with high S-lignin content released more glucose after pretreatment compared to G-lignin enriched plants [139].…”