Molecular Approaches for Transgene Containment and Their Potential Applications in Horticultural Crops - Transgenic Horticultural Crops: Challenges and Opportunities - page 291

structure.or.function.of.the.genital.organs..To.create.sterility.in.higher.plants,.male.
and.female.organs.have.been.targeted.for.manipulation..Several.types.of.male.and.
female.sterility.technologies.have.been.developed. 14,16,17
The. irst. group. of. sterility. genes. is. cytotoxin. genes.. Cytotoxin. genes. used. for.
creating. sterility. include. ribonuclease. genes. such. as. the. bacterial. barnase. gene.
cloned.from.a.soil.bacterium,. Bacillus amyloliquefaciens , 16,18-24 .diptheria. toxin.A.
chain. (DTA;. ADP-ribosyl-transferase), 25,26 . and. the. ribosome. inactivating. protein.
(RIP). 27 .Mariani.et.al. 23 .used.a.tobacco.tapetum-speciic.gene.promoter.(TA29).to.
control.the.expression.of.the.bacterial.barnase.gene.in.tobacco.and.oilseed.plants.
and. induced. male. sterility.. Expression. of. the. barnase. gene. destroyed. the. tapetal.
cells.and.successfully.prevented.pollen. formation,. thereby. producing.male-sterile.
plants.. Because. the. expression. of. the. barnase. gene. was. restricted. to. tapetum. tis-
sues,. vegetative.growth. and. loral. development. of. the. transgenic. plants.were. nor-
mal.. Similarly,. female. sterility. has. been. achieved. using. the. same. barnase. gene..
Goldman 28 .used.a.stigmatic.secretory.zone-speciic.gene.promoter.sequence,.the.5′.
untranslated.region.of.the. STIG1 .gene.cloned.from.tobacco.plants,.to.drive.the.
expression.of.the.barnase.gene..The.pistils.of.transgenic.plants.that.expressed.
the. STIG1 ::barnase. gene.underwent. normal. development. but.lacked. the. stigmatic.
secretory.zone.and.therefore.became.female.sterile..The.pollen.grains.of.the.trans-
genic.plants.could.germinate.on.the.ablated.stigmatic.surface.although.they.failed.
to.penetrate.the.transmitting.tissue.of.the.style,.suggesting.that.pollen.was.normal..
Using. a. developing. seed-speciic. gene. promoter,. the. FBP7 . gene. promoter. cloned.
from. petunia,. to. control. the. expression. of. the. barnase. gene. in. tobacco. plants,.
Colombo.et.al. 29 .were.able.to.generate.transgenic.plants.that.produced.no.ovules.or.
seeds..The. FBP7 .promoter.was.speciically.active.in.the.coat.of.developing.seeds.
and. is. completely. silent. in. the. gametophytically. derived. tissues.. Because. normal.
seeds.were.produced.if.wild-type.plants.were.pollinated.with.transgenic.plants,.the.
pollen.of.the. FBP7 ::barnase.plants.was.fertile.
A.large.body.of.experimental.evidence.has.demonstrated.that.the.bacterial.bar-
nase.gene.is.highly.effective.to.produce.sterile.plants.when.expressed.in.reproductive.
organs.. However,. barnase. expression. sometimes. also. results. in. deleterious. effects.
on.vegetative.growth.of.transgenic.plants.if.its.expression.is.leaky.and.affects.non-
target.organs. 30 .The.bacterial.barstar.protein,.a.potent.inhibitor.of.barnase,.has.been.
used. successfully. to. restore. fertility. of. barnase-mediated. sterility 23 . although. the.
eficacy. of. the. barstar. gene. can. vary. 30,31 . Also,. there. are. concerns. that. the. bacte-
rial. barnase.protein. may.be.toxic. to.humans. and.animals. because. barnase.can. be.
a.poison.for.human.and.animal.cells. 32-34 .Even.though.it.is.unclear.whether.minute.
amounts.of.the.bacterial.barnase.protein.present.in.transgenic.crops.can.be.of.harm.
to.humans.and.animals,.the.use.of.a.barnase.gene.in.edible.horticultural.crops.should.
be.avoided..For.nonedible.horticultural.crops.in.which.seeds.or.fruits.are.not.used.
for.human.and.animal.consumption,.the.barnase.gene.would.provide.an.outstanding.
tool.for.inducing.sterility.
A.second.group.of.genes.that.can.be.used.to.produce.sterility.is.one.involved.in.
speciic. metabolic. pathways. in. higher. plants.. For. example,. inhibition. of. pyruvate.
dehydrogenase.production.in.mitochondria.resulted.in.male.sterility. 35 .Tissue-speciic.
repression.of.an.extracellular.invertase,.Nin88,.caused.male.sterility. 21 .Disruption.of.