title: Genetic engineering ofArabidopsisto overproduce disinapoyl esters, potential lignin modification molecules.
abstract: 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 inArabidopsisto increase the amounts of DSEs by overexpressingsinapoylglucose:sinapoylglucose sinapoyltransferase(SST) 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 anSST-overexpression construct into thesinapoylglucose accumulator1(sng1-6) mutant (SST-OEsng1-6) which lacks several of the enzymes that would otherwise compete for the SST substrate, sinapoyglucose. Introduction ofcinnamyl alcohol dehydrogenase-c(cad-c) andcad-dmutations into theSST-OEsng1-6line further increased DSEs. Surprisingly, areduced epidermal fluorescence(ref) phenotype was observed whenSST-OEsng1-6plants 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.
authors.affiliation: Department of Biochemistry, Purdue University, West Lafayette, IN 47907 USA.|Center for Plant Aging Research, Institute for Basic Science (IBS), Daegu, 711-873 Republic of Korea.
authors.forename: Shinyoung
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, IN 47907 USA.
authors.forename: Huaping
authors.initials: H
authors.lastname: Mo
authors.affiliation: Department of Biochemistry, Purdue University, West Lafayette, IN 47907 USA.
authors.forename: Jeong Im
authors.initials: JI
authors.lastname: Kim
authors.affiliation: Department of Biochemistry, Purdue University, West Lafayette, IN 47907 USA.
authors.forename: Clint
authors.identifier: 0000-0002-5195-562X
authors.initials: C
authors.lastname: Chapple
keywords: Arabidopsis; Carboxypeptidase; Lignin; Metabolite; Phenylpropanoid; Sinapoyl