Unique Lignin Genetic Variants Tailored for Conversion Pathways

Cell Wall MoleculesC3Bio research has demonstrated that, regardless of specific conversion process, plant cell wall structural complexity at molecular, nanoscale, and mesoscale levels impacts the yields and selectivities of desired reaction products from catalytic and pyrolytic transformations. We are genetically modifying the composition and architecture of cell wall components to optimize post-conversion product yields without compromising pre-conversion biomass yields. From a deep knowledge of lignin biosynthesis, we developed control science methods to chemically induce lignification, modify its monolignol composition, and quantify its extent (Tobimatsu et al. 2013, Kim et al. 2014). Lignin is a phenylpropanoid-derived heteropolymer mainly comprised of guaiacyl (G) and syringyl (S) subunits. However, genetic disruption of lignin biosynthesis frequently results in stunted growth and developmental abnormalities, the mechanisms of which are poorly understood. C3Bio researchers showed that the phenotype of a lignin-deficient Arabidopsis mutant is dependent on the transcriptional coregulatory complex Mediator (Bonawitz et al. 2014). Cell walls of rescued med5a/b ref8 plants contain a novel lignin consisting almost exclusively of p-hydroxyphenyl (H) lignin subunits, and exhibit substantially facilitated yields of glucose and xylose upon hydrolysis.

Cell Wall Molecules Therefore, it is possible to create high H lignin plants with greatly reduced biomass recalcitrance, while at the same time avoiding the severe yield penalty normally associated with loss of G and S lignin. This observation suggests that G and S lignin subunits are largely dispensable for normal growth and development and that C3Bio re-design strategies to produce S-aldehyde, G-aldehyde and other novel genetic variants of lignin could lead to bioenergy crops tailored for specific downstream chemical catalyses.

 

References

Bonawitz, Nicholas D.; Kim, Jeong Im; Tobimatsu, Yuki; Ciesielski, Peter N.; Anderson, Nickolas A.; Ximenes, Eduardo; Maeda, Junko; Ralph, John; Donohoe, Bryon S.; Ladisch, Michael; and Chapple, Clint (2014) Disruption of Mediator rescues the stunted growth of a lignin-deficient Arabidopsis mutant. Nature, 509:376-380.

Kim JI, Ciesielski PN, Donohoe BS, Chapple C, Li X (2014) Chemically-induced conditional rescue of the ref8 mutant of Arabidopsis thaliana reveals rapid restoration of growth and selective turnover of secondary metabolite pools. Plant Physiol. 164:584-595.

Tobimatsu Y, Wagner A, Donaldson L, Mitra P, Niculaes C, Dima O, Kim JI, Anderson N, Loque D, Boerjan W, Chapple C, Ralph J (2013) Visualization of plant cell wall lignification using fluorescence-tagged monolignols. Plant J. 76:357-366.

 

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