Engineering hydroxyproline-O-glycosylated biopolymers to reconstruct the plant cell wall for improved biomass...

Reconstructing the chemical and structural characteristics of the plant cell wall represents a promising solution to overcoming lignocellulosic biomass recalcitrance to biochemical deconstruction. This study aims to leverage hydroxyproline (Hyp)-O-glycosylation, a process unique to plant cell wall glycoproteins, as an innovative technology for de novo design and engineering in planta of Hyp-O-glycosylated biopolymers (HypGP) that facilitate plant cell wall reconstruction. HypGP consisting of 18 tandem repeats of "Ser-Hyp-Hyp-Hyp-Hyp" motif or (SP4)₁₈ was designed and engineered into tobacco plants as a fusion peptide with either a reporter protein enhanced green fluorescence protein or the catalytic domain of a thermophilic E1 endoglucanase (E1cd) from Acidothermus cellulolyticus. The engineered (SP4)₁₈ module was extensively Hyp-O-glycosylated with arabino-oligosaccharides, which facilitated the deposition of the fused protein/enzyme in the cell wall matrix and improved the accumulation of the protein/enzyme in planta by 1.5-11-fold. The enzyme activity of the recombinant E1cd was not affected by the fused (SP4)₁₈ module, showing an optimal temperature of 80°C and optimal pH between 5 and 8. The plant biomass engineered with the (SP4)₁₈ -tagged protein/enzyme increased the biomass saccharification efficiency by up to 3.5-fold without having adverse impact on the plant growth.