Biofuel

Plant biomass (or "lignocellulose") is one of the greatest untapped reserves on the planet and is mostly composed of cell walls. Energy-rich polysaccharide polymers make up about 75% of plant cell walls and, in theory, these can be broken down to produce sugar substrates (saccharification) from which bioethanol can be produced by fermentation. However, the complex structure of cell walls, consisting of a network of cellulose microfibrils and matrix polysaccharides (hemicellulose; pectin) encrusted by the phenolic polymer lignin, make them very resistant to degradation. Plant biotechnology has a role to play in optimizing the cell walls of dedicated biofuel crop plants for saccharification.

 

Our research in re-engineering the plant cell walls for biofuel involves many scientific disciplines: plant transformation, biochemistry, carbohydrate chemistry and molecular biology. Currently we are involved in two projects: Bio4Bio – a national research program and an EU FP7-project Renewall.

 

 

Bio4bio

The shikamate pathway connects primary carbohydrate metabolism with the synthesis of the three aromatic amino acids tryptophane, tyrosine and phenylalanine. These three amino acids serve in plants as precursors for secondary metabolites particularly lignin. In this project lignin biosynthesis will be downregulated in Brachypodium using anti-sense technology against the first enzyme in the shikamate pathway, the 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPS).

Primarily because of lignin biosynthesis, more than 20% of total photosynthetically fixed carbon is estimated to flow through the shikimate pathway. In transgenic Brachypodium plants with reduced lignin content the unfixed carbon will be directed into the synthesis of new carbon polymers (link til Tom Hamborg).

 

Renewall

Renewall is a large international project which aims to optimise plant cell walls for biofuel applications by making them more readily converted into fermentable sugars for alcohol production. The project is divided into several workpackages (WP) and we contribute to WP3 (WP leader; Henrik V. Scheller) and WP5 (WP leader; Bodil Jørgensen).

The aim of WP3 is to increase our understanding of the cell wall matrix polysaccharides in order to optimise biomass potential. In this more fundamental WP we contribute with studies of how a group of glycosyltransferase candidate genes (DUF266) determine cell wall assembly. Another major contribution to WP3 is the production of Brachypodium transformants.

 

The research in WP5 is to evaluate the saccharification potential when manipulating cell walls by expressing microbial cell wall modifying or degrading enzymes in plants. We contribute with transgenic Brachypodium plants that process their xylan post harvest. With this approach we expect a more easily disassembled wall.

 

Selected publications:

Bernhard Borkhardt, Jesper Harholt, Peter Ulvskov, Birgitte K. Ahring, Bodil Jørgensen and Henrik Brinch-Pedersen. Autohydrolysis of plant xylans by apoplastic expression of thermophilic bacterial endo-xylanases. Plant Biotechnology Journal (2010) 8, pp. 1–12.