Characterization Of Cell Wall Structural Features That Predominately Affect Plant Growth And Biomass Saccharification

Plant cells walls are majorly composed of cellulose, hemicellulose, lignin and wall proteins. Cell wall structures play a vital role in morphogenesis, cell expansion and differentiation, intercellular communication, water movement, and responses to certain external stimuli. Plant cell walls represent the most abundant renewable biopolymer for bioethanol production.In principle, biomass conversion into biofuels involves three major steps: physical and chemical pretreatments for wall polymer disassociation, enzymatic hydrolysis for soluble sugar release, and yeast fermentation for ethanol production. As plant cell walls have evolved a complex structural and chemical mechanism to protect cells from microbial and animal kingdoms attack, lignocellulose recalcitrance fundamentally decides a costy biomass process with secondary environmental pollution. The recalcitrance is principally determined by wall polymer composition and polymer interaction styles. To reduce recalcitrance, genetic modification of plant cell walls has been proposed as a promising solution. Since plant cell wall modification could affect plant growth and development, however, it becomes essential to find out the key factor of plant cell walls that could not only enahnce biomass enzymatic digestibility, but also maintain plant grain yield and quality. In terms of three major issues(biomass pretreatment and enzymatic digestion, energy crop selection, and lignocellulose biosynthesis), three major projects have been completed as described below:1. Using a large population of Miscanthus germplasm accessions, we performed a systems biology analysis and found that the degree of arabinose substitution in xylan(Ara/Xyl) was the key factor that largely enhances biomass enzymatic digestibility under various chemical and physical pretreatments by reducing cellulose Cr I.2. Based on the systems biological analysis of 36 distinct cell wall mutants, we identified that the hemicellulosic Ara level negatively affected cellulose Cr I for enhancing both biomass enzymatic digestibility and plant lodging resistance in rice. Furthermore, two rice elite mutants, Osfc17 and Osfc30, were characterized wit a normal plant growth and high biomass enzymatic sccharification.3. Using unique rice mutant(Osfc16), we found that Os CESA9 site-mutation affected CSC association and reduced life-time of Os CESA4,7,9 complexes for consistently low-DP cellulose synthesis, which leads to low-Cr I cellulose production. The reduced cellulose Cr I significantly improved plant lodging resistance and biomass enzymatic digestibility. Global gene expression analysis suggests that the Os CESA9 fully-conserved-site mutation may simultaneously turn on multiple transcription factors and kinase regulations to maintain mutant growth as wild type.