title: Restricting lignin and enhancing sugar deposition in secondary cell walls enhances monomeric sugar release after low temperature ionic liquid pretreatment.
abstract: BACKGROUND
  Lignocellulosic biomass has the potential to be a major source of renewable sugar for biofuel production. Before enzymatic hydrolysis, biomass must first undergo a pretreatment step in order to be more susceptible to saccharification and generate high yields of fermentable sugars. Lignin, a complex, interlinked, phenolic polymer, associates with secondary cell wall polysaccharides, rendering them less accessible to enzymatic hydrolysis. Herein, we describe the analysis of engineered Arabidopsis lines where lignin biosynthesis was repressed in fiber tissues but retained in the vessels, and polysaccharide deposition was enhanced in fiber cells with little to no apparent negative impact on growth phenotype.
  
  
  RESULTS
  Engineered Arabidopsis plants were treated with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate 1-ethyl-3-methylimidazolium acetate ([C2C1im][OAc]) at 10 % wt biomass loading at either 70 °C for 5 h or 140 °C for 3 h. After pretreatment at 140 °C and subsequent saccharification, the relative peak sugar recovery of ~26.7 g sugar per 100 g biomass was not statistically different for the wild type than the peak recovery of ~25.8 g sugar per 100 g biomass for the engineered plants (84 versus 86 % glucose from the starting biomass). Reducing the pretreatment temperature to 70 °C for 5 h resulted in a significant reduction in the peak sugar recovery obtained from the wild type to 16.2 g sugar per 100 g biomass, whereas the engineered lines with reduced lignin content exhibit a higher peak sugar recovery of 27.3 g sugar per 100 g biomass and 79 % glucose recoveries.
  
  
  CONCLUSIONS
  The engineered Arabidopsis lines generate high sugar yields after pretreatment at 70 °C for 5 h and subsequent saccharification, while the wild type exhibits a reduced sugar yield relative to those obtained after pretreatment at 140 °C. Our results demonstrate that employing cell wall engineering efforts to decrease the recalcitrance of lignocellulosic biomass has the potential to drastically reduce the energy required for effective pretreatment.
authors.affiliation: Deconstruction Division, Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, Berkeley, CA USA ; Biological and Materials Science Center, Sandia National Laboratories, Livermore, CA USA.
authors.forename: Chessa
authors.initials: C
authors.lastname: Scullin
authors.affiliation: Deconstruction Division, Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, Berkeley, CA USA ; Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA USA.
authors.forename: Alejandro G
authors.initials: AG
authors.lastname: Cruz
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA USA.
authors.forename: Yi-De
authors.initials: YD
authors.lastname: Chuang
authors.affiliation: Deconstruction Division, Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, Berkeley, CA USA ; Biological and Materials Science Center, Sandia National Laboratories, Livermore, CA USA.
authors.forename: Blake A
authors.initials: BA
authors.lastname: Simmons
authors.affiliation: Feedstocks Division, Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, Berkeley, CA USA ; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA.
authors.forename: Dominique
authors.initials: D
authors.lastname: Loque
authors.affiliation: Deconstruction Division, Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, Berkeley, CA USA ; Biological and Materials Science Center, Sandia National Laboratories, Livermore, CA USA ; Joint BioEnergy Institute, 5885 Hollis Street, Emeryville, CA 94608 USA.
authors.forename: Seema
authors.initials: S
authors.lastname: Singh
keywords: Arabidopsis; Biofuels; Cell wall; Ionic liquid; Lignin; Saccharification