Why genetic modification of lignin leads to low-recalcitrance biomass

Abstract

Genetic modification of plants via down-regulation of cinnamyl alcohol dehydrogenase leads to incorporation of aldehyde groups in the lignin polymer. The resulting lignocellulosic biomass has increased bioethanol yield. However, a molecular-scale explanation of this finding is currently lacking. Here, we perform molecular dynamics simulation of the copolymer with hemicellulose of wild type and the genetically modified lignin, in aqueous solution. We find that the non-covalent association with hemicellulose of lignin containing aldehyde groups is reduced compared to the wild-type. This phase separation may increase the cell wall porosity in the mutant plants, thus explaining their easier deconstruction to biofuels. The thermodynamic origin of the reduced lignin-hemicellulose association is found to be a more favorable self-interaction energy and less favorable interaction with hemicellulose for the mutant lignin. Furthermore, reduced hydration water density fluctuations are found for the mutant lignin, implying a more hydrophobic lignin surface. The results provide a detailed description of how aldehyde incorporation makes lignin more hydrophobic and reduces its association with hemicellulose, thus suggesting that increased lignin hydrophobicity may be an optimal characteristic required for improved biofuel production.

Conformations of Low‐Molecular‐Weight Lignin Polymers in Water

“…Pretreated transgenic biomass with this less polar lignin produces higher yields of ethanol than the wild‐type . Previous simulations have explained this finding by a looser lignin–hemicellulose association . However, the present results suggest an additional explanation; that the genetically modified, less polar lignin should have a more spherical shape and lower surface area than more polar wild‐type lignin of the same molecular weight.…”

“…Molecular dynamics (MD) simulations of wild‐type lignin have probed high‐molecular‐weight lignin (degree of polymerization, d.p.=60) shape and dynamics as well as its interaction with cellulose and hemicellulose . Finally, the mutation of lignin in silico yielded macromolecular properties that are consistent with the phenotype of transgenic plants …”

Enzyme mediated biomass pretreatment and hydrolysis: a biotechnological venture towards bioethanol production

“…3,4 The recalcitrance of lignin is either reduced by oxidoreductive enzymes or changing the cell wall phenotype. 5 Physical, chemical and phsyico-chemical modes of biomass pretreatment and hydrolysis are more competent because of good conversion but associated with more energy consumption, hemicellulose solubilization and generation of intermediates or by-products. 6 Comparatively, enzymatic processes are target oriented and can be executed under mild process conditions with high product specicity.…”

Different Routes for Conifer- and Sinapaldehyde and Higher Saccharification upon Deficiency in the Dehydrogenase CAD1

“…This mechanism consequently leads to (1) lignin with fewer hydroxyl functions (i.e. one aldehydic carbonyl function for each hydroxycinnamaldehyde coupled into a b-ether structure, as opposed to two hydroxyl functions for canonical monolignols coupled into a b-ether structure), and consequently lignin that is more hydrophobic, which may reduce its noncovalent associations with hemicelluloses (Carmona et al, 2015). In addition, the mechanism leads to (2) b-ether moieties with conjugated g-carbonyl functionalities.…”