Deciphering biomarkers of the plant cell-wall recalcitrance: towards enhanced delignification and saccharification

Lignocellulosic biomass is the most abundant renewable resource on earth, composed of agricultural waste, food processing byproducts, and other wastes which are thrown in nature and, unfortunately, non-valorized. It is a rich substrate recognized for its compositional and structural diversities, with a high interest in the production of green biofuels and chemical platform molecules, which are extremely sought after in the actual world energetic transition scenario. Although it represents a great opportunity for green industries, breaking down the plant cell wall (PCW) is technically not as affordable as thought before, and the development of green biorefineries depends on optimizing plant resources, process fluxes, prioritizing integrated strategies, and before all the above-mentioned, solving the plant recalcitrance issue. Converting biomass starts with the dissociation of its elements, which should be figured out in light of its compositional and structural complexities. Field and postharvest strategies like the genome-wide selection of biorefinery crops and the knowledge-based choice of appropriate harvesting periods were suggested to answer this challenge. Although these practices helped improve the processability of bioenergy crops, they did not reach promising levels and should be further improved by their combination with state-of-art engineering technologies. In this sense, genetic tailoring of the PCW biosynthetic genes and the application of integrated pretreatment strategies are interesting and in-depth explained here. In this comprehensive review, we discuss novel aspects related to the importance and richness of lignocellulose feedstock in the biorefinery concept, the recalcitrance of PCW and biomarkers as a roadmap approach to diagnosing it, and finally, state-of-art strategies to overcome it towards an enhanced delignification and saccharification. All with the same main perspective: making the most of lignocellulose in added-value biorefinery applications.