Designing Plant Cell Walls that Fall Apart (3 of 3) (IMAGE)
Caption
Introducing really cleavable linkages into the lignin polymer backbone. Lignins are polymers integral to plant cell walls derived from combinatorial radical polymerization of hydroxycinnamyl alcohol monomers. Delignification requires cleavage of the polymer into smaller soluble units, but breaking even the weakest backbone bonds, so-called β-ethers, requires stringent chemical conditions. As conceptually shown here, we have introduced novel ferulate units (orange) bearing readily cleavable bonds, ester linkages (as designated here by simple twist-ties) to normal lignin monomers, into the backbone of the polymer in engineered Poplar trees. This was accomplished by inducing the plants to synthesize monolignol ferulate conjugates in their monomer pool and to utilize them for lignification. Doing so produces lignins that are more easily depolymerized, providing less energy-demanding access to the valuable plant polysaccharides. [The blue units represent the main interunit linkages in lignins, the so-called β-ethers; other units, such as the resinol (β–β-coupled units, purple) that start the lignin chain, are in other colors]. This image relates to a paper that appeared in the 4 April, 2014, issue of Science, published by AAAS. The paper, by Curtis Wilkerson at Michigan State University in East Lansing, MI, and colleagues was titled, "Monolignol Ferulate Transferase Introduces Chemically Labile Linkages into the Lignin Backbone."
Credit
[Graphic design by Matt Wisniewski, Media Specialist, Great Lakes Bioenergy Research Center, Madison, WI]
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