WP 2 - Genetic improvement of poplar wood quality for saccharification

WP Leader: Dr. Wout BOERJAN (Flanders Institute for Biotechnology, VIB)

Objectives:

The overall objective of WP2 is to make poplar clones that have improved properties as raw material for bio-ethanol production.

The major bottle-neck in the saccharification process of wood to fermentable sugars is lignin. Lignin is an aromatic polymer that locks-up the cellulose microfibrils, limiting their access by cellulases. Not only the total amount of lignin is important, but also its structure. The predominant units in the lignin polymer in angiosperms are coniferyl and sinapyl alcohol, and polymerization of these units gives rise to various linkages, the frequency of which determines the degradability of the polymer by various methods. For example, lignin made up predominantly of sinapyl alcohol is easier to degrade than lignin mainly made up by coniferyl alcohol, at least for chemical pulping. Ideally, woody cell walls would be rich in cellulose and poor in lignin. Additionally, lignin would be made up preferentially by syringyl units to reduce the degree of lignin condensation. The final quality of the wood is reflected in its saccharification potential. Saccharification is the enzymatic conversion of lignocellulosic biomass to fermentable sugars. The amount of glucose released by treating the lignocellulosic biomass with an enzyme cocktail containing cellulases and hemicellulases is proportional to the amount of bioethanol that can be produced from this biomass. Recent data indicate that the yield of ethanol from poplar wood can be increased by altering the quality of lignin (PAG XV meeting; San Diego) and recent data from VIB show that CCR-deficient Arabidopsis mutants with less lignin release 3-fold more glucose than wild type plants.

There are two main strategies to obtain genetically improved bioenergy poplars. One is by conventional breeding, the other by genetic engineering. For neither of these strategies, significant research towards bio-ethanol has been carried out. The aim of WP2 is to make significant and fast progress in our understanding of improved poplar genotypes that are easier to saccharify, within the time frame of the project and this information will be used to generate new and novel genotypes within WP3.



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