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which.are.compounds.derived.from.the.amino.acid.phenylalanine..Small.amounts.
of. the. apocarotenoids. β-ionone. and. 6-methyl-5-hepten-2-one. are. also. detectable.
in. the. fragrance. proile. 33,46 . Many. of. these. compounds. have. been. removed. from.
the.petunia.volatile.proile.through.silencing.of.regulatory.and.biosynthetic.genes.
(Table.3.2)..A.reduction.in.multiple.benzenoid.compounds.was.achieved.by.silenc-
ing. odorant1 . ( ODO1 ),. a. transcription. factor. that. regulates. transcription. of. genes.
important.for.supplying.substrates. for.loral.volatile.production. 47 .β-Ionone.emis-
sion. was. reduced. by. approximately. 50%. in. transgenic. petunias. with. RNA. inter-
ference. (RNAi)-suppressed. CCD1 . 33 . While. emission. of. β-ionone. is. low,. only.
detectable. in. picogram. quantities,. the. published. human. odor. threshold. is. low.
(0.007.nL.L −1 ).compared.to.other.more.abundant.volatiles.in.petunia. 33,48 .Therefore,.
β-ionone. could. potentially. be. important. in. the. overall. fragrance. of. petunia.. The.
clove-like.component.of.petunia.scent.was.removed.from.the.fragrance.proile.by.
suppression.of. coniferyl alcohol acyltransferase .( CFAT ).expression. 49 .CFAT.cata-
lyzes.the.acetylation.of.coniferyl.alcohol.to.form.coniferyl.acetate,.the.precursor.of.
isoeugenol.and.eugenol..The.two.volatile.compounds.imparting.rosy,.loral.notes.to.
petunia.fragrance.were.reduced.by.silencing. phenylacetaldehyde synthase ( PAAS )..
Transgenic. RNAi. suppressed. PAAS. plants. had. reduced. phenylacetaldehyde. and.
2-phenylethanol.levels. 50 .Dexter.et.al. 51 .and.Orlova.et.al. 52 .removed.benzyl.benzoate.
and.phenethylbenzoate.from.the.petunia.fragrance.by.RNAi-induced.silencing.of.
benzyl CoA:benzyl alcohol/phenylethanol benzoyl transferase . ( BPBT ).. Silencing.
of. benzoic acid/salicylic acid carboxyl methyltransferase1 . and. 2 . ( BSMT1 . and.
BSMT2 ). led. to. a. reduction. in. methylbenzoate,. the. most. predominant. volatile. of.
petunia. fragrance.. Flowers. lacking. normal. methylbenzoate. levels. had. a. distinct,.
detectable.change.in.fragrance,.and.80%.of.human.olfactory.panelists.were.able.to.
distinguish.them.from.control.lowers. 53
Increasing. lux. through. existing. biosynthetic. pathways. and. introducing. new.
fragrance. pathways. are. a. means. to. make. novel. fragrance. proiles. (Table. 3.2).. For.
example,.petunia.lowers.that.smell.more.like.a.rose.could.be.developed.by.increas-
ing.2-phenylethanol.synthesis.and.decreasing.levels.of.endogenous.volatiles,.which.
may.mask.the.perception.of.rose.aroma..Petunias.that.produced.more.intense.rose-
like. 2-phenylethanol. were. developed. by. introducing. tomato. phenylacetaldehyde
reductase .( LePAR ).into.the.petunia.genome. 54 .Introduction.of.a.strawberry.alcohol.
acyltransferase.( SAAT ).gene.into.petunia.did.not.affect.the.volatile.proile. 55 .Feeding.
isoamyl.alcohol,.a.substrate.of.SAAT,.to.the.transgenic.tissue.resulted.in.emission.
of. acetyl. ester. products.. Lücker. et. al. 56 . introduced. the. Clarkia breweri S-linalool
synthase . gene. into. petunia.. However,. plants. did. not. produce. linalool. and. instead.
accumulated. a. nonvolatile. conjugated. form.. Linalool. was. detected. in. transgenic.
CbLIS Dianthus caryophyllus .cultivar.'Eilat'.plants. 57 .While.these.plants.produced.
linalool. and. derivatives. thereof,. the. transgenic. lowers. did. not. smell. differently.
from.control.lowers.in.human.olfaction.tests..It.will.be.of.interest.to.introduce.the.
LIS.gene.into.a.different.background.of.carnation.that.has.less.fragrance.since.it.is.
possible.that.there.was.masking.by.other.volatile.compounds.
The. reports.discussed. in. this.section.unequivocally.demonstrate.that. loral.fra-
grance.can.be.engineered..A.number.of.important.issues.can.be.highlighted,.includ-
ing. (1). altering. fragrance. proiles. with. heterologous. genes. is. possible. and. will. be.
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