Downregulation of C3′H or C4H in Eucalyptus urophylla × Eucalyptus grandis Leads to Increased Sugar Extractability

Lignin reduction has the potential to reduce costs in biomass processing and lignocellulosic ethanol industries. National Renewable Energy Laboratory's Angela Ziebell and her colleagues developed two sets of Eucalyptus urophylla × Eucalyptus grandis: an RNAi downregulated in p-coumaroyl quinate/shikimate 3′-hydroxylase (C3'H) and an RNAi downregulated in cinnamate-4-hydroxylase (C4H). The team then characterized the lignin structure of both lines.

Both C3′H and C4H lines had significantly higher extractability, indicating altered cell wall construction. However, analysis showed that the molecular weight and structure of lignin in both downregulated lines were only slightly altered compared to the control and does not explain the higher extractability. Further analysis showed that the difference in extractability was due to the difference in total lignin content between the lines.

This means that overall lowered lignin content and not the change in structure or molecular weight of lignin, contributes greatly to reduced recalcitrance and increased extractability of cell wall biopolymers.