Transgenic Ornamental Crops - Transgenic Horticultural Crops: Challenges and Opportunities - page 68

have.extended.vase.life. 77-80 . ACO .cosuppressed.carnation.plants.had.approximately.
a. twofold. longer. vase. life. than. control. lowers. 78 . Suppression. of. ACO . in. Torenia
fournieri .extended.lower.life.up.to.3.5-fold.longer.than.controls. 81 .While.these.low-
ers.produce.less.ethylene.and.have.longer.vase.life,.the.lowers.are.still.sensitive.to.
exogenous. sources. of. ethylene.. Thus,. much. of. the. focus. on. engineering-improved.
lower.life.has.centered.on.manipulations.of.ethylene.receptor.and.signaling.proteins.
Inhibiting Ethylene Responses by Disrupting Ethylene Signal Transduction
Ethylene.is.perceived.by.plants.through.transmembrane.receptor.proteins,.which.are.
encoded.by.the. ethylene resistant .(ETR).gene.family,.typically.consisting.of.ive.or.
more.genes.in.plants..The.receptors.have.been.identiied.in.expressed.sequence.tag.
(EST).collections.from.more.than.20.plant.species,.including.monocots,.dicots,.and.
lower.vascular.plants. 82 .Binding.of.the.hormone.has.been.demonstrated.in.cyanobac-
teria,.fungi,.green.alga,.lower.vascular.plants,.and.angiosperms. 83,84 .While.studies.of.
receptor.function.at.the.molecular.level.have.not.been.carried.out.in.many.plant.spe-
cies.outside.of.Arabidopsis.and.tomato,.the.proteins.are.highly.conserved.in.regions.
that.are.functionally. important. 82,84 .It.is.therefore. likely.that.the.receptors.act.in.a.
similar.fashion.in.plant.species.other.than.tomato.and.Arabidopsis,.that.is,.as.nega-
tive.regulators.of.ethylene.responses..In.the.absence.of.ethylene,.ethylene.responses.
are.repressed,.and,.in.the.presence.of.ethylene,.repression.of.ethylene.responses.is.
lifted..Arabidopsis.plants.carrying.the. etr1-1 .mutation.are.almost.completely.insen-
sitive.to.ethylene. 85 .Another.central.component.of.the.pathway,. ethylene insensitive 2.
(EIN2),.is.critical.for.ethylene.signaling..Arabidopsis.EIN2.loss-of-function.mutants.
are.unable.to.respond.to.ethylene. 86 .Both.ETR.and.EIN2.are.critical.to.plant.ethylene.
responses,.making.them.good.candidates.for.manipulating.ethylene.responses.at.the.
molecular.level.
Floral.longevity.has.been.extended.in.transgenic.plants.with.altered.ethylene.sig-
naling..Petunias.with.longer-lasting.lowers.have.been.attained.by.overexpression.of.
the.mutant.ethylene.receptor.allele,. etr1-1 ,.from. Arabidopsis thaliana 87 .and.by.sup-
pressing.expression.of. EIN2 .by.RNAi.or.cosuppression. 88 .Petunia.corollas.expressing.
the.Arabidopsis. etr1-1 .gene.do.not.wilt.after.pollination.or.exposure.to.ethylene.and.
often.stay.attached.to.the.receptacle.until.the.developing.fruit.detaches.the.corolla,.
up.to.10.days.after.pollination.compared.to.2-3.days.for.control.lowers.. EIN2 .RNAi.
and. EIN2 .cosuppression.petunia.plants.also.display.delayed.corolla.senescence.after.
pollination.or.exposure.to.exogenous.ethylene..These.lowers.do.not.exhibit.visual.
signs. of. senescence. until. more. than. 9-12. days. after. pollination. 88 . Similarly,. con-
stitutive. expression. of. the.Arabidopsis. etr1-1 .in.carnation.doubled.the.vase.life.of.
carnation.lowers. 80,89 .Constitutive.expression.of.a.melon.etr1-1-like.mutant.receptor.
in. Nemesia strumosa .resulted.in.lowers.that.lasted.1-3.days.longer.than.controls. 90
Transgenic.plants.expressing.constitutive.ethylene.insensitivity.not.only.prove.the.
concept.that.genetically.disrupting.ethylene.signaling.will.extend.lower.life.but.have.
also.been.useful.as.a.tool.for.learning.about.the.myriad.of.processes.that.ethylene.is.
involved.with.in.a.plant.life.cycle..For.example,.35S:: etr1-1 .petunias.are.unable.to.be.
vegetatively. propagated. due. to. an. inability. to. form. adventitious. roots 91 . and. exhibit.
higher.mortality.than.control.plants. 88 .Both.of.these.issues.are.huge.horticultural.limi-
tations..The.problems.likely.can.be.overcome.through.the.use.of.promoters.that.restrict.