Stacking Multiple Traits for High Yield of Fermentable Sugars in Plant Biomass

Second-generation biofuels help decrease dependency on fossil fuels. To make biomass more suitable for biorefinery use, researchers need to better understand plant cell wall synthesis. Increasing the ratio of C6 to C5 sugars in the cell wall and decreasing the lignin content are two important targets in engineering of plants that are more suitable for biofuel production. Aude Aznar and Camille Chalvin of Lawrence Berkeley National Laboratory have identified genes involved in the synthesis of pectic galactan, including the GALS1 and URGT1.

Their team aimed to engineer plants with increased pectic galactan in stems. To do this, they used plants that were already engineered to have low xylan content, then further engineered them to overexpress GALS1, URGT1, and UGE2, a UDP-glucose epimerase. Finally, the high galactan and low xylan traits were again stacked with the low lignin trait, which was achieved by expressing the QsuB gene encoding dehydroshikimate dehydratase in lignifying cells.

These results show that increasing C6 sugar content, decreasing xylan, and reducing lignin content can be combined in an additive manner, leading to improved properties in terms of biofuel production, without any negative growth effects.