Cascading of engineered bioenergy plants and fungi sustainable for low-cost bioethanol and high-value biomaterials under green-like biomass processing

Plant cell walls contain the most abundant sustainable biomass resource for biofuels and biomaterials on the earth. However, lignocellulose recalcitrance generally requires a costly biomass process unacceptable for large-scale bioethanol production with the potential formation of secondary wastes. To address this bottleneck-like biomass recalcitrance issue, this review attempts to connect recent innovation progress regrading up-stream lignocellulose modification, middle-stream cellulases production and down-stream biomass processing. Particularly, the site-specific gene editing is demonstrated for precise and mild modification of plant cell walls to generate recalcitrance-much-reduced cellulose nanofibers, which not only leads to little impact on plant strength and biomass yield, but also causes remarkably enhanced enzymatic saccharification in major bioenergy crops. By selecting the size-reduced cellulose nanofibers of engineered bioenergy crops as enzyme-inducing substrate, fungal strains are then engineered to secret the optimal cellulases enzymes cocktails enabled for complete enzymatic saccharification of diverse lignocellulose residues from cost-effective biomass pretreatments. Consequently, engineered yeast strains could use both hexoses and xylose released from complete saccharification as carbon sources for maximum bioethanol production by an efficient co-fermentation. Finally, the green-like processing technology is introduced to generate biomaterials and biochemicals by using the remaining lignin-rich residues. Therefore, this work has originally proposed a novel strategy that dynamically cascades the engineered bioenergy crops and fungal strains with the advanced biomass process technology, which should be considered as next generation of integrated biotechnology for both cost-effective biofuels production and value-added bioproducts with minimum waste releases into the environment.