Characterization Of The Key Factors Of Cell Wall Composition And Polymer Features That Predominately Affect Biomass Enzymatic Digestibility In Wheat Straw

Wheat is an important food crop with enormous biomass residues for biofuels. However, lignocellulosic recalcitrance causes unacceptably costly biomass process. Because biomass recalcitrance is determined by plant cell wall composition and wall polymer features, genetic modification of plant cell walls has been proposed as a promising solution to biomass recalcitrance. Hence, it is essential to identify the key factors of plant cell walls that greatly affect lignocellulose enzymatic saccharification But, little is yet known about plant cell wall impacts on biomass enzymatic digestibility in wheatIn this study, I initially observed agronomic traits, and then determined cell wall composition and biomass digestibility in total115wheat accessions. Furthermore, I detected the cell wall polymer features of10wheat standard accessions, and compared with3distinct rice mutants. Here are main points proposed in the study:1. Large variations were observed in terms of the agronomic traits and cell wall compositions (cellulose, hemicelluloses and lignin) in the115wheat accessions. In particular, the coefficient variations (CV) ranged from16.7%to47.4%about the agronomic traits, whereas the cell wall compositions varied from4.7%to13.6%, indicating a genetic diversity in the wheat accessions.2. Under1%NaOH pretreatment and the sequential cellulases hydrolysis at two concentrations (1.6,3.2g/L), total115wheat accessions exhibited large variations on biomass enzymatic saccahrification (hexoses yields against cellulose level) with CV from6.6%to21.2%. Notably, the highest hexoses yields could respectively reach54.6%and94.0%under two concentrations of cellulases hydrolysis.3. Integrative analysis showed that the three major wall polymers (cellulose, hemicelluloses and lignin) average levels were31.77%,31.27%and21.73%in115wheat accessions. Compared with rice, wheat contains much more lignin level Correlative analysis indicated that hemicelluloses and lignin levels both negatively affected biomass enzymatic digestibility upon1%NaOH pretreatment, in particular on the KOH-extractable hemicelluloses and the acid-insoluble lignin. By contrast, the agronomic traits and biomass yields could not significantly affect biomass enzymatic hydrolysis.4. Using the10representative wheat accessions and the3distinct rice mutants, their three major wall polymer features were detected, and also the hexoses yields were determined under NaOH and H2SO4pretreatments at three concentrations (0.5%/0.25%,1%,4%). The results suggested that three major wall polymers levels should not be the dominated factors that affect biomass enzymatic digestibility compared with wall polymer features upon various chemical pretreatments in wheat.5. With regards to the three major wall polymer features, biomass enzymatic digestibility was predominantly affected either negatively by cellulose crystallinity (CrI) of raw biomass materials, or positively by both arabinose (Ara) substitution degree of the non-KOH-extractable hemicelluloses (reverse Xyl/Ara) and p-coumaryl alcohol (H) relatively proportion of the KOH-extractable lignin (H or H/G). It has suggested that β-1,4-glucans may have an interaction with either the branched Ara of the non-KOH-extractable hemicelluloses or the KOH-extractable H-monomer via the hydrogen bands that could reduce cellulose crystallinity for high biomass enzymatic saccharification in wheat and rice.In conclusion, the study has identified the key factors of plant cell walls that predominately affect biomass enzymatic digestibility in wheat It has provided insights into biomass enzymatic hydrolysis, and also suggested the potential of genetic modification of plant cell walls for high biomass saccharification in wheat and beyond.