(227b) Increasing C6 Cell Wall Sugar Content By Engineering the Accumulation of a Low Recalcitrance Polysaccharide in Plants

Increasing C6 cell wall sugar content by engineering the accumulation of a low recalcitrance polysaccharide in plants

Miguel E. Vega-Sánchez, Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, USA.

The production of biofuels from lignocellulose remains a challenging process due primarily to the inherent resistance of plant cell walls to deconstruction (commonly referred to as recalcitrance). In addition, the presence of significant amounts of 5 carbon (C5) sugars in plant biomass that are not readily fermented by microorganisms is another obstacle to efficient conversion to fuels. For these reasons, reduced cell wall recalcitrance and increased C6 monosaccharide content are desirable traits in potential biofuel crops, as long as these biomass modifications do not significantly alter normal growth and development. Mixed-linkage glucan (MLG), a cell wall polysaccharide comprised of glucose monomers linked by both b-1,3 and b-1,4 bonds, is a good example of a low recalcitrance and C6-containing polymer. As opposed to cellulose, MLG is non-linear and cannot aggregate into microfibrils due to the presence of the b-1,3 bonds, which makes it more soluble in aqueous environments. We have previously shown that Nicotiana benthamiana plants transiently over-expressing the rice mixed-linkage glucan synthase CslF6 using a 35S promoter accumulate large amounts of MLG (over 10% of dry weight). However, previous data in barley and our own results in N. benthamiana have shown that constitutive production of MLG in plants severely compromises growth and development. In order to bypass these negative effects, we have successfully developed a strategy to engineer Arabidopsis plants to accumulate significant amounts of MLG in the cell wall without growth defects. This approach offers a new engineering alternative to enhance cell wall properties of lignocellulosic biofuel crops.