Plant cell walls represent an enormous biomass resource for the generation of biofuels
and chemicals. As lignocellulose property principally determines biomass recalcitrance,
the genetic modification of plant cell walls has been posed as a powerful solution.
Here, we review recent progress in understanding the effects of distinct cell wall
polymers (cellulose, hemicelluloses, lignin, pectin, wall proteins) on the enzymatic
digestibility of biomass under various physical and chemical pretreatments in herbaceous
grasses, major agronomic crops and fast-growing trees. We also compare the main factors
of wall polymer features, including cellulose crystallinity (CrI), hemicellulosic
Xyl/Ara ratio, monolignol proportion and uronic acid level. Furthermore, the review
presents the main gene candidates, such as CesA, GH9, GH10, GT61, GT43 etc., for potential
genetic cell wall modification towards enhancing both biomass yield and enzymatic
saccharification in genetic mutants and transgenic plants. Regarding cell wall modification,
it proposes a novel groove-like cell wall model that highlights to increase amorphous
regions (density and depth) of the native cellulose microfibrils, providing a general
strategy for bioenergy crop breeding and biofuel processing technology.