Transgenic Ornamental Crops - Transgenic Horticultural Crops: Challenges and Opportunities - page 58

In nonlegumes,.THC.is.quickly.converted.to.naringenin.by.chalcone.isomerase,.which.
closes.the.central.ring.of.THC.leading.to.synthesis.of.lavanones..However,.in.legumes,.
such. as. Medicago truncatula and Glycine max ,. chalcone. reductase. (CHR). reduces.
THC.to.6′-deoxychalcone. 11 .Transgenic.petunias.expressing. Medicago CHR .in.a.white.
lowering.background.accumulate.novel.6′-deoxychalcones,.have.lower.levels.of.lavo-
nols,.and.exhibit.a.pale.yellow.corolla.color.while.a.pale.purple.color.is.observed.when.
the.transgene.is.expressed.in.a.purple.petunia.background. 12
Aurones.are.a.class.of.lavonoids.produced.from.chalcones.that.give.lowers.bright.
luorescent.yellow.colors..They.often.provide.nectar.guides.for.visiting.pollinators.
and.have.a.more.limited.species.distribution.in.plants. 13,14 .In. Antirrhinum ,.the.chal-
cone.THC.undergoes.glucosylation.and.oxidative.cyclization.to.produce.aurones. 15 .
Yellow. Torenia hybrida .lowers.were.created.from.a.line.normally.producing.blue.
lowers.by.silencing.native.dihydrolavonol.4-reductase.(DFR).expression.and.intro-
ducing.two. Antirrhinum .genes.for.aurone.biosynthesis. 14 .By.blocking.anthocyanin.
accumulation. and. expressing. the. Antirrhinum . aureusidin. synthase. and. chalcone.
4′- O -glucosyltransferase. genes,. aurones. accumulated. and. were. not. masked. by. the.
blue.malvidin-type.anthocyanins.normally.accumulating.in.the.Summer.Wave.Blue.
Torenia .cultivar.
Anthocyanins
Anthocyanins.give.lowers.red,.orange,.blue,.and.violet.hues..They.are.synthesized.
in.the.cytosol.from.lavonones.and.accumulate.in.the.vacuole.where.molecular.inter-
actions,. vacuolar. pH,. ion. cofactors,. and. cellular. shape. all. contribute. to. the. inal.
visual.effect..There.are.six.main.groups.of.anthocyanins:.cyanidin,.delphinidin,.mal-
vidin,.pelargonidin,.peonidin,.and. petunidin..Their. synthesis. begins.with. the. pro-
duction.of.dihydrolavonols.when.hydroxyl.groups.are.positioned.on.the.lavonones.
by.lavanone.3-hydroxylase.(F3H),.lavonone.3′-hydroxylase.(F3′H),.and.lavanone.
3′5′-hydroxylase.(F3′5′H).(Figure.3.1)..Dihydrolavonols.are.reduced.to.leucoantho-
cyanidins. by. DFR.. DFR. substrate. preference. is. variable. in. different. plant. species.
and.represents.a.critical.entry.point.in.color.production.
Lack. of. F3′5′H. activity. is. associated. with. the. absence. of. blue. coloration. in.
many.families.of.lowering.plants,.including.carnation.(reviewed.by.Chandler.and.
Tanaka 16 ).. Blue. color. has. been. introduced. into. carnation. through. introduction. of.
petunia.F3′5′H.and.DFR.genes.into.a.white.lowered.background.lacking.DFR.and.
F3′H. activity. 16 . Transgenic. carnations. expressing. both. of. these. genes. accumulate.
the.delphinidin.type.anthocyanins. 17 .These.blue-violet.transgenic.carnations,.mar-
keted.as.the.Moon.series,.were.developed.by.Florigene.Pty..Ltd..and.Suntory.Ltd..
and.are.the.irst.and.only.transgenic.ornamental.to.date.that.has.been.successfully.
commercialized.. While. F3′H. and. F3′5′H. activities. are. important. for. blue. color.
other.factors.including.co-pigments.and.coordinating.metal.ions.are.also.key.fac-
tors. in. determining. blue. color.. Cyanidin. type. anthocyanins. are. packaged. into. a.
supermolecular.complex.to.give.blue.color.to.lowers.of.blue.cornlower.while.the.
same.anthocyanins.give.red.color.to.rose. 18 .The.brilliant.blue.color. in.cornlower.
is.attributed.to.a.tetranuclear.complex.of.cyanidin.anthocyanin,.a.lavone,.and.che-
lating. Fe 3+ ,. Mg 2+ ,. and. Ca 2+ . ions.. An. understanding. of. the. genetics. contributing.