The multiple phenylpropene synthases in both Clarkia breweri and Petunia hybrida represent two distinct protein lineages

Plant J. 2008 May;54(3):362-74. doi: 10.1111/j.1365-313X.2008.03412.x. Epub 2008 Jan 16.


Many plants synthesize the volatile phenylpropene compounds eugenol and isoeugenol to serve in defense against herbivores and pathogens and to attract pollinators. Clarkia breweri flowers emit a mixture of eugenol and isoeugenol, while Petunia hybrida flowers emit mostly isoeugenol with small amounts of eugenol. We recently reported the identification of a petunia enzyme, isoeugenol synthase 1 (PhIGS1) that catalyzes the formation of isoeugenol, and an Ocimum basilicum (basil) enzyme, eugenol synthase 1 (ObEGS1), that produces eugenol. ObEGS1 and PhIGS1 both utilize coniferyl acetate, are 52% sequence identical, and belong to a family of NADPH-dependent reductases involved in secondary metabolism. Here we show that C. breweri flowers have two closely related proteins (96% identity), CbIGS1 and CbEGS1, that are similar to ObEGS1 (58% and 59% identity, respectively) and catalyze the formation of isoeugenol and eugenol, respectively. In vitro mutagenesis experiments demonstrate that substitution of only a single residue can substantially affect the product specificity of these enzymes. A third C. breweri enzyme identified, CbEGS2, also catalyzes the formation of eugenol from coniferyl acetate and is only 46% identical to CbIGS1 and CbEGS1 but more similar (>70%) to other types of reductases. We also found that petunia flowers contain an enzyme, PhEGS1, that is highly similar to CbEGS2 (82% identity) and that converts coniferyl acetate to eugenol. Our results indicate that plant enzymes with EGS and IGS activities have arisen multiple times and in different protein lineages.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Clarkia / enzymology*
  • Clarkia / genetics
  • Clarkia / metabolism
  • Electrophoresis, Polyacrylamide Gel
  • Enzymes / genetics
  • Enzymes / metabolism*
  • Eugenol / analogs & derivatives
  • Eugenol / chemistry
  • Eugenol / metabolism
  • Flowers / enzymology
  • Flowers / metabolism
  • Molecular Sequence Data
  • Molecular Structure
  • Petunia / enzymology*
  • Petunia / genetics
  • Petunia / metabolism
  • Phylogeny
  • Plant Proteins / classification
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Sequence Homology, Amino Acid


  • Enzymes
  • Plant Proteins
  • Eugenol
  • isoeugenol