Altering the relative abundance of hydroxycinnamic acids enhances the cell wall digestibility of high-lignin sugarcane

Abstract

Agricultural production of energy crops such as sugarcane (Saccharum spp. L) will be necessary to ensure a reliable supply of cellulosic feedstock to manufacture future renewable products such as biofuels. Complete enzymatic saccharification of this cellulosic material is challenging. Targeted breeding of sugarcane to attain specific cell wall characteristics could improve cell wall digestibility (CWD). With the goal of devising criteria for choosing suitable sugarcane candidates, we measured the CWD and cell wall composition (lignin, structural polysaccharides, hydroxycinnamic acids (HCA), and lignin monomers) of stalk tissue from 34 sugarcane genotypes (Saccharum hybrids). CWD and acid insoluble lignin (AIL) were negatively correlated. The relative amount of syringyl and guaiacyl lignin monomers did not affect CWD. Individual HCA’s, p-coumaric acid (CA) and ferulic acid (FA), also influenced CWD but to a lesser extent than AIL. CWD was negatively correlated to etherified CA and FA but positively correlated to esterified FA. A CWD model was constructed using AIL and the esterified to etherified FA ratio as predictors. This empirical model explained 63% of the observed CWD variance. The model supported the notion that CWD could be improved by increasing the esterified to etherified FA ratio in conjunction with a moderate attenuation to lignification. This may be a promising tactic to avoid problems associated with low lignification.