A grass-specific cellulose–xylan interaction dominates in sorghum secondary cell walls

Abstract

Sorghum (Sorghum bicolor L. Moench) is a promising source of lignocellulosic biomass for the production of renewable fuels and chemicals, as well as for forage. Understanding secondary cell wall architecture is key to understanding recalcitrance i.e. identifying features which prevent the efficient conversion of complex biomass to simple carbon units. Here, we use multi-dimensional magic angle spinning solid-state NMR to characterize the sorghum secondary cell wall. We show that xylan is mainly in a three-fold screw conformation due to dense arabinosyl substitutions, with close proximity to cellulose. We also show that sorghum secondary cell walls present a high ratio of amorphous to crystalline cellulose as compared to dicots. We propose a model of sorghum cell wall architecture which is dominated by interactions between three-fold screw xylan and amorphous cellulose. This work will aid the design of low-recalcitrance biomass crops, a requirement for a sustainable bioeconomy.

Xylan Structure and Dynamics in Native Brachypodium Grass Cell Walls Investigated by Solid-State NMR Spectroscopy

“…It was suggested that grass xylan may have side-chain decorations incompatible with binding to cellulose in the Xn 2f conformation and that this Xn 2f conformation may arise only after dehydration. 37 The present study on never-dried Brachypodium tissues confirms that some xylan in grasses does indeed have branches that permit binding to cellulose in the Xn 2f conformation. 16 …”

Importance of Water in Maintaining Softwood Secondary Cell Wall Nanostructure

“…Recently, it was reported that xylan Ara f signals in an INADEQUATE experiment were reduced by lyophilization and rehydration of sorghum. 58 …”

Expanded analyses of the functional correlations within structural classifications of glycoside hydrolases

“…For instance, EC 3.2.1.4 (cellulases) and EC 3.2.1.8 (xylanases) both occurred in at least 8 different homologous superfamilies. Cellulose, as the most abundant polysaccharide on Earth, and hemicellulose with xylan as the main component together constitute plant cell wall material [45] , [46] . Therefore, we speculate that the large biomass and high degradation difficulty might be the reasons for the widespread multiorigin convergent evolution of the degradation activities of polysaccharides.…”