title: Eugenol synthase genes in floral scent variation in Gymnadenia species.
abstract: Floral signaling, especially through floral scent, is often highly complex, and little is known about the molecular mechanisms and evolutionary causes of this complexity. In this study, we focused on the evolution of "floral scent genes" and the associated changes in their functions in three closely related orchid species of the genus Gymnadenia. We developed a benchmark repertoire of 2,571 expressed sequence tags (ESTs) in Gymnadenia odoratissima. For the functional characterization and evolutionary analysis, we focused on eugenol synthase, as eugenol is a widespread and important scent compound. We obtained complete coding complementary DNAs (cDNAs) of two copies of putative eugenol synthase genes in each of the three species. The proteins encoded by these cDNAs were characterized by expression and testing for activity in Escherichia coli. While G. odoratissima and Gymnadenia conopsea enzymes were found to catalyze the formation of eugenol only, the Gymnadenia densiflora proteins synthesize eugenol, as well as a smaller amount of isoeugenol. Finally, we showed that the eugenol and isoeugenol producing gene copies of G. densiflora are evolutionarily derived from the ancestral genes of the other species producing only eugenol. The evolutionary switch from production of one to two compounds evolved under relaxed purifying selection. In conclusion, our study shows the molecular bases of eugenol and isoeugenol production and suggests that an evolutionary transition in a single gene can lead to an increased complexity in floral scent emitted by plants.
authors.affiliation: Institute of Systematic Botany, University of Zurich, 8008, Zurich, Switzerland, ethalok@yahoo.com.
authors.forename: Alok K
authors.initials: AK
authors.lastname: Gupta
authors.forename: Ines
authors.initials: I
authors.lastname: Schauvinhold
authors.forename: Eran
authors.initials: E
authors.lastname: Pichersky
authors.forename: Florian P
authors.initials: FP
authors.lastname: Schiestl
mesh_terms: D018076:DNA, Complementary / Q000235:genetics; D030541:Databases, Genetic; D005054:Eugenol / Q000031:analogs & derivatives / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D035264:Flowers / Q000201:enzymology* / Q000235:genetics; D008401:Gas Chromatography-Mass Spectrometry; D018506:Gene Expression Regulation, Plant; D015723:Gene Library; D063990:Gene Ontology; D017343:Genes, Plant; D058977:Molecular Sequence Annotation; D009812:Odorants; D029595:Orchidaceae / Q000201:enzymology* / Q000235:genetics*; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000235:genetics* / Q000378:metabolism; D012015:Reference Standards; D013045:Species Specificity
chemical_list: D018076:DNA, Complementary; D005054:Eugenol; C036643:isoeugenol; D044925:Oxidoreductases Acting on CH-CH Group Donors