Agriculture Reference
In-Depth Information
transgene. low. via. pollen.
254
. Examples. of. such. systems. include. pollen. sterility.
in. tobacco. and. oilseed. rape. with. a. barnase. gene. driven. by. a. tapetum-speciic.
promoter
255
. and. male. sterility. in. tobacco. with. constitutive. expression. of. the.
Agrobacterium rhizogenes
.rolC.sterility.gene.
256
.These.systems.have.been.shown.
to. be. successful. in. preventing. transgene. spread. from. GM. lowering. plants. into.
other. related. species.
254
. Since. most. crop. chloroplasts. genes. are. inherited. mater-
nally,.transgenes.inserted.into.the.plastid.genomes.are.unlikely.to.be.transmitted.
by. pollen. transmission.
35
. As. discussed. earlier,. transplastomic. plants. have. been.
extensively. used. for. PMP. expression. partially. due. to. their. advantage. in. ensur-
ing. transgene. containment.. To. further. reduce. the. risk. of. transgene. low-through.
pollination,.a.double.fail-safe.strategy.was.developed.using.combinations.of.both.
male. sterility. and. transplastomic. genomes.
257
. One. of. the. handicaps. of. the. male.
sterile.or.transplastomic.plants.is.that.they.can.still.be.pollinated.by.nontransgenic.
varieties,.and.the.resulting.hybrids.can.serve.as.pollen.donors.to.spread.transgene.
into. the. environment.. Transgene. mitigation. is. a. strategy. to. address. the. leakage.
and.unidirectionality.handicap.of.male.sterility.and.maternal.inheritance..In.this.
technology,.a.mitigation.gene,.which.encodes.a.trait.detrimental.to.wild.plants,.is.
genetically.linked.to.the.transgene.
258
.If.the.transgene.is.escaped.and.transmitted.
to.an.unintended.host.plant,.the.mitigation.gene.will.co-escape.with.the.transgene,.
and.its.expression.would.prevent.the.hybrid.from.competing.with.wild.plants.and.
setting.seed..For.example,.this.strategy.based.on.the.Arabidopsis.gibberellic.acid.
insensitive. gene. (Δ
gai
). was. able. to. induce. dwarism. in. tobacco. plants.. When.
Δ
gai
.transgenic.plants.or.hybrids.are.grown.together.with.wild-type.tobacco,.the.
dwarf.transgenic.or.hybrid.plants.cannot.compete.effectively.for.sunlight.with.the.
taller.wild-type.plants.for.photosynthesis.and.rarely.survive.to.set.seed,.therefore,.
preventing.the.establishment.of.transgene.in.the.population.
258
.Furthermore,.Δ
gai
.
gene.also.causes.male.sterility.in.tobacco.plants..The.combination.of.male.sterility.and.
mitigation.effect.of.Δ
gai
.makes.it.a.superb.gene.for.preventing.transgene.outlow.
and.for.mitigating.the.low.if.sterility.containment.failure.or.reverse.gene.inlux.
occurred.
254
. In. addition. to. pollens,. seeds. are. also. major. routes. of. transgene. and.
transgenic. product. spreading. by. human. errors. or. animal. activities.. To. resolve. this.
problem,.several.“genetic.use.restriction.technologies”.(GURT).including.the.“ter-
minator”. (US. patent. 5,723,765). and. its. alternatives. have. been. developed. to. pro-
duce. “conditional-sterilized”. seeds.
259
. Seeds. from. plants. engineered. with. these.
“terminator”-like.genes.are.usually.nonviable,.unless.the.plants.are.intentionally.
exposed.to.speciic.activating.molecules.or.environmental.stimulus..These.chemi-
cal. or. environmental. conditions. will. induce. the. expression. of. a. repressor. gene,.
which,.in.turn,.will.inactivate.the.terminator.gene..Several.such.technologies.have.
been.shown.to.be.effective.
260,261
.For.example,.transgenic.plants.carrying.the.bar-
nase. gene. routinely. produce. non-viable. seeds,. but. can. become. viable. only. after.
an. exposure. to. a. heat. treatment. at. 40°C.
261
. Such. seed. sterility. technologies. will.
allow.effective.blocking.of.transgene.lowthrough.volunteer.seeds.and.will.prevent.
recurrence.of.incidents.similar.to.the.ones.caused.by.ProdiGene..Inducible.expres-
sion. systems. have. been. developed. to. prevent. human,. animal,. and. environmen-
tal.exposure.to.plant.transgenic.protein.products..In.these.systems,.transgene.are.
driven.by.an.inducible.promoter.instead.of.a.constitutive.one..As.a.result,.transgene.
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