Second‐generation biofuels (B2G) generally uses residues composed of lignocellulosic materials to produce renewable energy (potentially up to 50%), without increasing the planted areas. However, the high cost of enzymes required for cell wall disassembly prior to the saccharification makes the B2G production more expensive yet, compared to the first‐generation biofuels. Designing plants with less lignin, a barrier to B2G production, or facilitating cell wall disassembly by searching for the plant mechanisms can be the way to obtain B2G feasibility. Therewith, plant cell wall proteomics provides valuable information concerning the main cell wall proteins (CWPs) involved in its biosynthesis and rearrangements. Essentially, two plants of the grass family have been studied: sugarcane as a crop amenable to second‐generation ethanol (E2G) production; and Brachypodium distachyon as a model plant amenable to genetic transformation. Cell wall proteomics has allowed the identification of numerous CWPs as well as their fine profiling in different organs and at various developmental stages. Proteins acting on carbohydrates, mostly glycosyl hydrolases, and oxidoreductases, including class III peroxidases and laccases, can be highlighted. Both kinds of CWPs are assumed to contribute to the remodelling of cell wall polysaccharides by enzymatic or non‐enzymatic mechanisms. CWPs present in growing organs could also be attractive candidates since they greatly contribute to cell wall plasticity.
Part of the book: Frontiers in Bioenergy and Biofuels
Glycoside hydrolases (GHs) are enzymes that are able to rearrange the plant cell wall polysaccharides, being developmental- and stress-regulated. Such proteins are used in enzymatic cocktails for biomass hydrolysis in the second-generation ethanol (E2G) production. In this chapter, we investigate GHs identified in plant cell wall proteomes by predicting their functions through alignment with homologous plant and microorganism sequences and identification of functional domains. Up to now, 49 cell wall GHs were identified in sugarcane and 114 in Brachypodium distachyon. We could point at candidate proteins that could be targeted to lower biomass recalcitrance. We more specifically addressed several GHs with predicted cellulase, hemicellulase, and pectinase activities, such as β-xylosidase, α and β-galactosidase, α-N-arabinofuranosidases, and glucan β-glucosidases. These enzymes are among the most used in enzymatic cocktails to deconstruct plant cell walls. As an example, the fungi arabinofuranosidases belonging to the GH51 family, which were also identified in sugarcane and B. distachyon, have already been associated to the degradation of hemicellulosic and pectic polysaccharides, through a peculiar mechanism, probably more efficient than other GH families. Future research will benefit from the information available here to design plant varieties with self-disassembly capacity, making the E2G more cost-effective through the use of more efficient enzymes.
Part of the book: Advances in Biofuels and Bioenergy