Breaking the “Glycomic Code” of Cell Wall Polysaccharides May Improve Second-Generation Bioenergy Production from Biomass

Plant cell walls display a highly complex organization that confers resistance (recalcitrance) to enzymatic hydrolysis. This poses a barrier to the development of technologies for second-generation bioenergy production due to the difficulty of enzymes in accessing wall polymers. Here, we examine the fine structure of some of the main cell wall hemicelluloses and present some evidences that lend support to the idea of a glycomic code, which can be defined as the diversity of encrypted results of the biosynthetic mechanisms of plant cell wall polysaccharides that give rise to fine-structural domains containing information in polysaccharides. These are responsible for the formation of polymer composites with different levels of polymer-polymer interactions and recalcitrance to hydrolysis. Polysaccharide motifs that are recalcitrant to hydrolysis are here called pointrons, and the ones that are available to enzyme attack are named pexons. From the biotechnological viewpoint, the understanding of the glycomic code will require further identification of pointrons and possibly the transformation of them into pexons so that walls would become suitable to hydrolysis. This is thought to be key for tackling the cell wall recalcitrance, therefore opening the way for efficient biomass disassembly and efficient bioenergy production.