Engineered cytosolic and chloroplastic UDP-glucose epimerases distinctly modulate xylan interplay for size-tunable...

The plant cell wall is a complex matrix critical for structural integrity, growth, and biomass utilization. This study investigates the distinct roles of cytosolic and chloroplastic UDP-glucose epimerases (CytoUGE and CpUGE) in regulating cell wall assembly and mechanical strength in Oryza sativa. By genetic modulation, we demonstrate that both CytoUGE and CpUGE enhance photosynthesis and increase the content of cellulose, hemicellulose, and lignin, thereby improving stem mechanical strength. Notably, CpUGE exerts a more pronounced effect on cellulose crystallinity while reducing xylan interference with cellulose microfibrils. Detailed monosaccharide analysis reveals that CpUGE promotes tighter xylan-lignin interactions and lower arabinose substitution in alkali-insoluble xylan, contributing to a more ordered cell wall architecture. Atomic force microscopy reveals that cellulose nanocrystals (CNCs) derived from CytoUGE exhibit a tendency to self-aggregate, forming structures of significantly larger dimensions. Moreover, modulation of both UGEs bidirectionally tunes CNC dimensions-overexpression enhances mechanical reinforcement, while loss-of-function reduces CNC size to increase reactivity. Integrate analyses identify the alkali-insoluble and soluble arabinose/xylose ratios as key indicators linking cell wall structure to mechanics. Our findings reveal that spatially separated UGE differentially regulate xylan interplay, providing a strategic target for engineering rice with improved cellulose quality for both agricultural and industrial applications.