Transgenic Ornamental Crops - Transgenic Horticultural Crops: Challenges and Opportunities - page 72

an. ortholog. of. the. Arabidopsis AGAMOUS . class. C. gene,. in. petunia. gives. rise. to.
lowers.with.stamens.converted.into.petal-like.structures. 115
Transgenic.manipulation.of.loral.organ.identity.genes.has.led.to.a.greater.under-
standing.of.the.molecular.mechanisms.underlying.lower.development.in.diverse.spe-
cies,.giving.us.the.required.knowledge.for.creating.morphologically.novel.lowers.with.
the.tools.of.biotechnology..Mutation.screens.have.been.the.primary.means.for.identi-
fying.lines.with.altered.loral.morphology.in.many.ornamental.crops..For.example,.a.
transposon.insertion.into. Duplicated .( DP) ,.a.C.class.gene,.caused.a.double.lower.phe-
notype.in.Japanese.morning.glory. 116 .Although.it.is.possible.to.obtain.altered.lower.
morphology.mutants,.biotechnology.will.be.useful.in.developing.lines.with.novel.lo-
ral.appearance.where.mutant.populations.are.dificult.to.generate.and.for.understand-
ing. the. basic. molecular. mechanisms. underlying. lower. development.. Sepals. were.
converted. into. purple. colored. petal-like. organs. when. green petal ,. a. class B. func-
tion. gene,. was. overexpressed. in. petunia. 117 . Antisense. repression. of. the. chrysanthe-
mum. AGAMOUS -like.gene.caused.conversion.of.pistils.to.petal.tissue.and.pistil-like.
tissue. 118 .Interesting.changes.to.petal.loral.morphology,.such.as.changes.in.ray.loret.
shape,.have.also.been.observed.when.expression.of.loral.homeotic.genes.is.altered.in.
Gerbera.(e.g.,.Yu.et.al. 119 )..Altering.petal.position.and.number.through.manipulation.
of.loral.organ.identity.genes.can.result.in.a.more.colorful,.showier.lower.and.lowers.
with.new.morphology,.both.of.which.are.traits.of.interest.for.consumers.
f ruIt and f lower S Ize
While. larger. lowers. are. often. selected. in. ornamental. breeding. programs,. only.
recently.has.this.trait.been.modiied.through.biotechnology..As.mentioned.in.Leaf.
Longevity.section,.cytokinins.are.a.class.of.phytohormones.that.promote.cell.divi-
sion;.therefore,.increasing.cytokinin.biosynthesis.is.a.strategy.toward.increasing.cell.
numbers.in.target.tissues..This.was.achieved.by.using.the. Arabidopsis thaliana AP3 .
promoter.to.drive.lower-speciic.expression.of.the. Agrobacterium tumefaciens ipt .
cytokinin. biosynthetic. gene. in. transgenic. petunia. 120 . AP3 . is. a. class. B. loral. organ.
identity. gene. specifying. petal. and. stamen. identity.. The. AP3 . promoter. restricts.
expression.to.the.petals.and.stamens.in.Arabidopsis 121 .and.to.loral.organs.in.petu-
nia. 120 .Five.independent.transgenic.AP3:: ipt .petunia.lines.had.increased.lower.diam-
eter.compared.to.control.lowers..Flowers.from.these.lines.had.a.20%-30%.increase.
in.the.diameters.of.individual.loral.organs.due.to.radial.expansion..Transgenic.lines.
had.lowers.with.over.90%.increase.in.fresh.weight.compared.to.controls..Some.lines.
had.>60%.increase.in.overall.fruit.weight.while.others.had.fruit.weights.similar.to.
those.of.controls.
A grobActerium rhizogenes rol G eneS
The. rol . genes. from. Agrobacterium rhizogenes . have. been. useful. for. changing.
.multiple.aspects.of.plant.architecture.(reviewed.by.Casanova.et.al. 122 )..There.are.four.
rol .genes.( rolA ,. B ,. C ,.and. D ),.with. rolC .(cytokinin-β-glucosidase).having.the.most.
potential. for. transgenic. enhancement. of. ornamental. plants.. In. vivo. the. rol . genes.
interfere.with.phytohormone.metabolism.and.modify.secondary.metabolism,.which.