Genetic engineering of to overproduce disinapoyl esters, potential lignin modification molecules.

Background: Monolignol-like molecules can be integrated into lignin along with conventional monolignol units, and it has been shown that the incorporation of non-canonical subunits can be used to generate hydrolysable lignin by introduction of ester linkages into the polymer and that this type of lignin is more easily removable. Disinapoyl esters (DSEs), which to some degree resemble the monolignol sinapyl alcohol, may be promising lignin modifying units for this purpose. As a first step toward determining whether this goal is achievable, we manipulated metabolic flux in to increase the amounts of DSEs by overexpressing () which produces two main DSEs, 1,2-disinapoylglucose, and another compound we identify in this report as 3,4-disinapoyl-fructopyranose.

Results: We succeeded in overproducing DSEs by introducing an -overexpression construct into the (-) mutant (-OE -) which lacks several of the enzymes that would otherwise compete for the SST substrate, sinapoyglucose. Introduction of - (-) and - mutations into the -OE - line further increased DSEs. Surprisingly, a () phenotype was observed when -OE - plants were evaluated under UV light, which appears to have been induced by the sequestration of DSEs into subvacuolar compartments. Although we successfully upregulated the accumulation of the target DSEs, we did not find any evidence showing the integration of DSEs into the cell wall.

Conclusions: Our results suggest that although phenylpropanoid metabolic engineering is possible, a deeper understanding of sequestration and transport mechanisms will be necessary for successful lignin engineering through this route.