Abstract text: Recalcitrance, the resistance of plant biomass to enzymatic deconstruction, has been primarily attributed to a molecular interaction between lignin and cellulose that prevents hydrolysis by cellulolytic enzymes. However, in poplar, fiber cell-cell adhesion at the compound middle lamellae (CML) substantially limits diffusion of the hydrolytic enzymes and contributes to recalcitrance (Yang et al. 2020, Plant Biotechnol. 18:1027). Sugarcane and sweet sorghum represent two major high-biomass grasses for production of biofuels and bioproducts. Because of the unique features of the cell walls of grasses, we examined the chemical and enzymatic treatments that disrupt cell-cell adhesion. As in poplar, sugarcane and sorghum required sequential treatment of woody rind particles with sodium chlorite to first oxidize the phenylpropanoids, followed by dilute NaOH to disrupt cell-cell adhesion. Rhamnogalacturonan-I (RG-I) lyase could replace alkali treatment for cell separation of woody rind particles delignified with sodium chlorite. Thus, despite its low abundance in primary walls of grasses, RG-I is a common CML component in both type I and type II walls and functions in cell-cell adhesion. Genetic control of CML composition through modification of RG-I and lignin/phenylpropanoids provides a strategy to facilitate biomass deconstruction that is common to all angiosperm feedstocks.

This work was supported by the National Laboratory of the Rockies (NLR), Laboratory Directed Research and Development (LDRD) program, and Instituto Nacional de Ciência e Tecnologia do Bioetanol – INCT do Bioetanol (FAPESP 2014/50884-5 and CNPq 465319/2014-9).