Rewriting Resistance: Genetic Changes Increase Crops’ Biomass and Sugar Release

The Science

A major barrier to using switchgrass, poplars, and other plants to make fuels is the natural resistance of plant cell walls to deconstruction. To overcome this resistance to deconstruction, a detailed understanding of the structure and genetics of plant cell walls is essential. In this study, scientists targeted a specific gene associated with plant cell wall formation (GAUT4) in switchgrass and poplar. Thus, they could examine the impact of this gene on biomass yield and resistance to deconstruction. They found that plants with a downregulated GAUT4 exhibited greater biomass yield and greater sugar release upon deconstruction even after a 3-year field trail. The study demonstrates a potentially vital tool for developing dedicated bioenergy crops.

The Impact

This is the first example of a specific plant cell wall structural modification that resulted in increased biomass yield and sugar release in both woodyand grassy biofuel feedstocks. This research also illustrates the impact of pectin cross linkages within cell wall polymers. Further, the research highlights the impact of engineering reduced pectin linkages in cell walls on sugar release from the deconstructed biomass.

Summary

Scientists at the BioEnergy Science Center used targeted engineering of plant cell wall polymers to genetically modify switchgrass and poplar, promising bioenergy grassy and woody crops, to improve the biomass yield and ethanol production. Scientists accomplished this modification by downregulating the gene, GAUT4, which reduced the activity and production of two cell wall pectin polymers, homogalacturonan and rhamnogalacturonan II. These changes lead to loosened plant cell walls with increased cell expansion, plant growth, and polymer accessibility during the sugar release process. All downregulated GAUT4-KD grasses and trees showed enhanced growth in the greenhouse and improved enzymatic sugar release and fermentation into ethanol, an important biofuel. GAUT4-KD switchgrass lines grown 3 years in the field provide up to 7-fold increased extractability of cell wall sugars and ethanol production, and 6-fold more biomass yield over field-grown controls. This study shows that GAUT4 is an effective gene target for improved biomass production with improved properties for fuel production.

Funding

The research was primarily funded by the BioEnergy Science Center and partially by the Center for Bioenergy Innovation, which are Department of Energy (DOE) Bioenergy Research Centers supported by the Office of Biological and Environmental Research in the DOE Office of Science.

Publication

A.K. Biswal, M.A. Atmodjo, M. Li, et al., “Sugar release and growth of biofuel crops are improved by downregulation of pectin biosynthesis.” Nature Biotechnology 36, 249 (2018). [DOI: 10.1038/nbt.4067]