Modifying lignin to improve bioenergy feedstocks: strengthening the barrier against pathogens?†

Abstract

Lignin is a ubiquitous polymer present in cell walls of all vascular plants, where it rigidifies and strengthens the cell wall structure through covalent cross-linkages to cell wall polysaccharides. The presence of lignin makes the cell wall recalcitrant to conversion into fermentable sugars for bioenergy uses. Therefore, reducing lignin content and modifying its linkages have become major targets for bioenergy feedstock development through either biotechnology or traditional plant breeding. In addition, lignin synthesis has long been implicated as an important plant defense mechanism against pathogens, because lignin synthesis is often induced at the site of pathogen attack. This article explores the impact of lignin modifications on the susceptibility of a range of plant species to their associated pathogens, and the implications for development of feedstocks for the second-generation biofuels industry. Surprisingly, there are some instances where plants modified in lignin synthesis may display increased resistance to associated pathogens, which is explored in this article.

Expression Profiling in Pinus pinaster in Response to Infection with the Pine Wood Nematode Bursaphelenchus xylophilus

“…One of the main end products of this pathway is lignin. This polymer is determinant for the trees stability and robustness, acting mainly as physical barrier to pathogens [52]. Regulation of lignin components production is controlled by peroxidase (EC: 1.11.1.7).…”

Función de la Lignina en la Interacción Planta-Nematodos Endoparásitos Sedentarios

“…Lignification is a highly coordinated process, and is regulated by a set of harmonized metabolic events; so far the action of 10 enzymes have been identified in the monolignols synthesis process (Sattler and Funnell-Harris, 2013). In the different species of plants, the synthesis of most of these enzymes is directed by the action of different genes and proteins present in multiple isoforms that vary in their kinetic properties and their distribution in the plant; however, the large amount of substrates, as well as the extense family of genes has made it difficult to identify and characterize the isoforms that are specifically involved in the lignification process (Bonawitz and Chapple, 2010).…”

Bioethanol: Feedstock Alternatives, Pretreatments, Lignin Chemistry, and the Potential for Green Value-Added Lignin Co-Products

“…As a hydrophobic polymer, lignin offers structural support to cell walls [41]. Lignin forms an evaporation barrier and it has a critical role in channeling water throughout the plant.…”

“…These lignins are the by-products of phenolation, methylation, demethylation, hydrolysis and other modifications to protolignin [41]. Once industrial lignins are extracted they can be further modified to form secondary products such as additives for concrete products, dyes, epoxies and thermoplastics.…”

“…Lignin forms an evaporation barrier and it has a critical role in channeling water throughout the plant. It protects against parasitic and enzymatic attack by reducing porosity [41]. Lignin emerges from enzymatic dehydrogenative polymerization of three phenylpropanoid precursors: p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol ( Figure 2).…”