Breeding Targets to Improve Biomass Quality in Miscanthus

Abstract

Lignocellulosic crops are attractive bioresources for energy and chemicals production within a sustainable, carbon circular society. Miscanthus is one of the perennial grasses that exhibits great potential as a dedicated feedstock for conversion to biobased products in integrated biorefineries. The current biorefinery strategies are primarily focused on polysaccharide valorization and require severe pretreatments to overcome the lignin barrier. The need for such pretreatments represents an economic burden and impacts the overall sustainability of the biorefinery. Hence, increasing its efficiency has been a topic of great interest. Inversely, though pretreatment will remain an essential step, there is room to reduce its severity by optimizing the biomass composition rendering it more exploitable. Extensive studies have examined the miscanthus cell wall structures in great detail, and pinpointed those components that affect biomass digestibility under various pretreatments. Although lignin content has been identified as the most important factor limiting cell wall deconstruction, the effect of polysaccharides and interaction between the different constituents play an important role as well. The natural variation that is available within different miscanthus species and increased understanding of biosynthetic cell wall pathways have specified the potential to create novel accessions with improved digestibility through breeding or genetic modification. This review discusses the contribution of the main cell wall components on biomass degradation in relation to hydrothermal, dilute acid and alkaline pretreatments. Furthermore, traits worth advancing through breeding will be discussed in light of past, present and future breeding efforts.

Keywords: biomass quality; breeding; cell wall; cellulose; hemicellulose; lignin; lignocellulosic biomass; miscanthus; pretreatment; saccharification.

Figure 1

Schematic representation of the major constituents of the miscanthus secondary cell wall. The cellulose (A), glucuronoarabinoxylan (GAX) (B) and lignin (C) structures attempt to fairly represent the (relative) abundances of each individual structural moiety and the interactions between the polymers based on literature. Note that for simplicity only two types of diferulates (8-5 and 5-5) are shown, though many other linkage types are known to exist.