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Lignin is the primary contributor to the high cost of biofuel-production from lignocellulosic biomass. In order to study lignin removal and the release of aromatic monomers, we applied hydrocracking and ionic liquid pretreatments on Arabidopsis thaliana biomass from both wild type (WT) and a mutant (CAD cxd) defective in two cinnamyl alcohol dehydrogenase genes involved in the lignin biosynthetic pathway. For Arabidopsis WT, our results highlight that pretreatments reduce average molecular weight of lignin by about 65% and decrease the content of β-O-4 linkages between lignin monomers. For Arabidopsis CAD mutant, an opposite effect is evidenced. Fewer differences were observed on depolymerization and molecular structure of lignin, which indicates that (8-O-4), (8-5), and (8-8) linkages observed in CAD mutant make lignin more resilient to pretreatment than wild-type lignin. Finally, our study shows the potential of hydrocracking pretreatment technology for extracting valuable aldehyde monomers such as vanillin and syringaldehyde from biomass.

Renewable and sustainable liquid transportation biofuels based on lignocellulosics conversion face several obstacles that must be overcome in order for them to become commercially viable and cost-competitive. The presence of lignin is one of the most significant contributors to biomass recalcitrance and consequently increases the costs associated with conversion. Lignins are complex aromatic biopolymers, derived from hydroxyphenylpropanoids, that vary in composition and structure as a function of genotype, phenotype, and environment, as well as with the cell type and maturity of the plant tissue. Lignins consist of (mainly) syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units, derived from sinapyl, coniferyl, and p-coumaryl alcohols. These units are not discrete within either the cell or a given lignin molecule, and the compositional ratios of these three moieties can vary significantly. This inherent complexity and heterogeneity of lignin, both in structure and composition, make it extremely difficult to develop a conversion technology that can efficiently process a wide range of sustainable feedstocks cost-effectively. There is a growing body of work that has demonstrated several genetic engineering strategies that, when coupled with an integrated approach to conversion, hold significant promise for the development of tailored feedstocks designed for biofuel production. The knowledgebase is at the point where researchers are also able to contemplate strategies to 'design' the lignin polymer for easier processing. The realization of advanced analytical techniques and an increasing number of plant genomes are enabling researchers to take a systems approach towards understanding and engineering lignin to develop these optimal feedstocks.

Lignin, a highly complex but integral part of plant cell wall , is indigestible and therefore a concern in biomass deconstruction for cost effective biofuel production. A way to address this issue is to manipulate the plant to generate a cell wall that is amenable to breakdown. However, little is know about the actual assembly of lignin during plant cell wall biosynthesis. Fluorescent Lifetime Imaging Microscopy (FLIM) utilizes the lifetime of the auto-fluorophore signal generated, rather than its intensity , to create an image. An interesting characteristic of lignin is that it is highly auto-fluorescent in the UV excitation region due to its phenolic ring composition. Thus, it may be possible to infer structural and organizational information of lignin polymerization using this imaging technique. In this study FLIM is used to resolve differences in lignification in the plant cell wall during development.