Down-regulation of C3′H and C4H Genes in Eucalyptus Improves Sugar Release for Ethanol Production

Understanding the interactions within the cell wall is vital to overcome recalcitrance of the lignocellulosic biomass for ethanol production. A major factor affecting recalcitrance is lignin, which can be manipulated by changes in its biosynthetic pathway.

 A research team led by Robert W. Sykes of the National Renewable Energy Laboratory down-regulated the expression of cinnamate 4-hydroxylase (C4H) or p-coumaroyl quinate/shikimate 3′-hydroxylase (C3′H) in eucalyptus and evaluated their cell wall composition and reduced recalcitrance.

Eucalyptus trees with down-regulated C4H or C3′H expression displayed lowered overall lignin content. The control samples had an average of 29.6 % lignin content, while C3′H and C4H reduced lines had an average of 21.7% and 18.9 % lignin, respectively. Both down-regulated lines also had different lignin compositions and reduced recalcitrance as indicated by increased sugar release.

Lowering lignin content was found to have the largest impact on reducing recalcitrance of the transgenic eucalyptus variants. The development of lower recalcitrance trees opens up the possibility of using alternative pretreatment strategies in biomass conversion processes that can reduce production costs.