Down-regulation of OsMYB103L distinctively alters beta-1,4-glucan polymerization and cellulose microfibers assembly for enhanced biomass enzymatic saccharification in rice

Using a novel rice Osfc9/myb103 mutant and OsMYB103L-RNAi transgenic line, this study examined that down-regulations of OsMYB103L could not significantly affect plant growth and development, but remarkably reduced cellulose level, crystallinity and polymerization without significant impacts in other major wall polymers (hemicellulose, lignin), which thereby resulted in distinct cellulose nanofiber assembly in plant cell walls. These consequently improved lignocellulose recalcitrance for much enhanced biomass enzymatic saccharification in mature rice straws. By performing multi-omics analyses integrated with DAP-seq assay, this work further demonstrated that OsMYB103L could act as an active transcription factor to specifically mediate cellulose biosynthesis and deposition by regulating OsCesAs genes and other genes associated with microfibril orientation and assembly. Hence, this study has not only provided insights into cellulose biosynthesis, but it also offered a powerful strategy for genetic modification of plant cell walls in bioenergy crops.