Agriculture Reference
In-Depth Information
lavonoid.biosynthesis.through.manipulation.of.chalcone.synthase.gene.expression.
could.lead.to.male.sterility.
36,37
.Overexpression.of.β-ketothiolase.via.integration.of.
the.transgenes.into.the.chloroplast.genome.of.tobacco.plants.produced.male.sterile.
phenotype.
38
.Expression.of.a.bacterial.enoyl-CoA.hydratase/lyase.enzyme,.which.led.
to. re-routing. of. the. phenylpropanoid. pathway,. and. an. unedited.
atp9
. gene,. a. pro-
tein.involved.in.the.proton.channel.of.ATP.synthase,.also.caused.male.sterility.
39-43
.
Compared.to.the.use.of.the.barnase.gene,.food.safety.concerns.over.transgenic.plants.
can.be.minimized.if.these.metabolic.genes.are.used.to.create.sterility..However,.the.
effectiveness.of.using.metabolic.genes.to.create.sterility.is.much.lower.than.that.of.
using.the.barnase.gene..Also,.the.eficacy.of.the.metabolic.genes.can.be.plant.spe-
cies.dependent..Pilot.studies.to.test.the.effectiveness.of.a.chosen.metabolic.gene.to.
produce.sterility.in.a.plant.species.of.interest.should.always.be.carried.out.before.it.
is.used.as.a.sterile.gene.tool.in.that.particular.crop.
The.third.group.of.useful.genes.to.create.sterility.involves.hormone.biosynthesis,.
catabolism.or.signaling.pathways.in.higher.plants..Plant.hormones.play.an.important.
role.in.the.reproductive.organ.development.and.altering.expression.of.genes.involved.
in. hormone. levels. or. response. in. reproductive. organs. often. can. lead. to. sterility..
For. instance,. an. inhibition. of. expression. of. an. ethylene-forming. enzyme,. l-ami-
nocyclopropane-l. carboxylate. oxidase,. in. pistils. was. effective. in. disrupting. ovule.
development. and. therefore. caused. female. sterility.
44
. Transgene-mediated. reduc-
tion. in. jasmonic. acid. concentration. in. anthers. led. to. male. sterility. due. to. defects.
in. anther. and. pollen. development.
45,46
. Expression. of. the.
rolC
. gene,. cloned. from.
Agrobacterium rhizogenes
,. resulted. in. male. sterility. and. reduced. female. fertility,.
presumably.due.to.the.RolC-mediated.changes.in.hormone.sensitivity.or.concentra-
tion.in.reproductive.organs.
47
.Tissue-speciic.overexpression.of.a.cytokinin.oxidase.
(
CKX1
).gene.involved.in.cytokinin.degradation.in.transgenic.maize.(Zea.mays).also.
produced.male-sterile.plants.
48
.Similarly,.expression.of.a.mutant.version.of.a.gibber-
ellins.receptor.gene.(gai).in.anthers.and.pollen.of.tobacco.and.
Arabidopsis
.caused.
the.abortion.of.these.reproductive.organs.
48
.Male.infertility.or.abnormal.male.organ.
development.as.a.result.of.expression.of.the.
CKX1
.could.be.restored.by.applications.
of.exogenous.cytokinins..Similar.to.the.Group.2.genes.discussed.earlier,.using.hor-
mone-related.genes.should.be.more.acceptable.by.the.public.regarding.food.safety.
issues..However,.the.effectiveness.of.these.hormone.genes.can.vary.from.one.plant.
species.to.another,.and.may.be.further.inluenced.by.environmental.factors.
A.fourth.group.of.genes.that.can.be.used.to.produce.sterility.is.homeotic.genes,.
important.for.loral.organ.development..Genetic.and.molecular.studies.demonstrate.
that. homeotic. genes. act. alone. and. together. to. specify. the. fate. of. loral. organ. pri-
mordia.in.higher.plants.(see.reviews.by.Ferrandiz,
49
.Lohmann.and.Weigel,
50,51
.Ma,
52
.
Weigel.and.Meyerowitz,
53
.and.Zik.and.Irish.
54
)..Sterility.can.be.achieved.by.ectopic.
expression. of. homeotic. genes.. For. example,. overexpression. of. the.
Brassica napus
AGAMOUS
.gene,.which.regulates.the.development.of.stamens.and.pistils,.leads.to.
the.conversion.of.stamens.into.carpel-like.structures.in.transgenic.tobacco.plants.
55
.
Expression. of. a. tobacco.
AGAMOUS
. homolog,.
TAG1
,. resulted. in. the. replacement.
of. stamens. with. petaloid. organs. and. the. conversion. of. pistils. to. nonreproductive.
organs.
56
. In. both. cases,. the. transgenic. plants. produced. were. male. sterile.. On. the.
other.hand,.Mitsuda.et.al.
57
.used.a.Chimeric.REpressor.Gene-Silencing.Technology.
Search WWH ::
Custom Search