title: The lack of floral synthesis and emission of isoeugenol in Petunia axillaris subsp. parodii is due to a mutation in the isoeugenol synthase gene.
abstract: Floral scent has been extensively investigated in plants of the South American genus Petunia. Flowers of Petunia integrifolia emit mostly benzaldehyde, while flowers of Petunia axillaris subsp. axillaris emit a mixture of volatile benzenoid and phenylpropanoid compounds that include isoeugenol and eugenol. Flowers of the artificial hybrid Petunia hybrida, a cross between P. integrifolia and P. axillaris, emit a similar spectrum of volatiles as P. axillaris subsp. axillaris. However, the flowers of P. axillaris subsp. parodii emit neither isoeugenol nor eugenol but contain high levels of dihydroconiferyl acetate in the petals, the main scent-synthesizing and scent-emitting organs. We recently showed that both isoeugenol and eugenol in P. hybrida are biosynthesized from coniferyl acetate in reactions catalyzed by isoeugenol synthase (PhIGS1) and eugenol synthase (PhEGS1), respectively, via a quinone methide-like intermediate. Here we show that P. axillaris subsp. parodii has a functional EGS gene that is expressed in flowers, but its IGS gene contains a frame-shift mutation that renders it inactive. Despite the presence of active EGS enzyme in P. axillaris subsp. parodii, in the absence of IGS activity the coniferyl acetate substrate is converted by an as yet unknown enzyme to dihydroconiferyl acetate. By contrast, suppressing the expression of PhIGS1 in P. hybrida by RNA interference also leads to a decrease in isoeugenol biosynthesis, but instead of the accumulation of dihydroconiferyl acetate, the flowers synthesize higher levels of eugenol.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Michigan, 830 North University Street, Ann Arbor, MI 48109-1048, USA.
authors.forename: Takao
authors.initials: T
authors.lastname: Koeduka
authors.forename: Irina
authors.initials: I
authors.lastname: Orlova
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Baiga
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Noel
authors.forename: Natalia
authors.initials: N
authors.lastname: Dudareva
authors.forename: Eran
authors.initials: E
authors.lastname: Pichersky
mesh_terms: D000085:Acetates / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D005054:Eugenol / Q000031:analogs & derivatives* / Q000378:metabolism; D035264:Flowers / Q000201:enzymology* / Q000235:genetics; D016368:Frameshift Mutation; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008969:Molecular Sequence Data; D009812:Odorants / Q000032:analysis; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000235:genetics / Q000378:metabolism*; D032306:Petunia / Q000201:enzymology* / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D018749:RNA, Plant / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013379:Substrate Specificity; D014835:Volatilization
chemical_list: D000085:Acetates; D010940:Plant Proteins; D018749:RNA, Plant; D005054:Eugenol; C036643:isoeugenol; D044925:Oxidoreductases Acting on CH-CH Group Donors