Transgenic Fruit and Nut Tree Crops Review - Transgenic Horticultural Crops: Challenges and Opportunities - page 19

Hepatitis.B.surface.antigen.(HBsAg).was.expressed.in.banana.plants. 206 .Hepatitis.B.
is.the.major.cause.of.persistent.viremia.in.humans,.and.banana.is.an.ideal.host.for.
expression.of.HBsAg.due.to.its.palatability.to.infants.and.year-round.availability.in.
the.tropics..By.expressing.an.HBsAg.“ s ”.gene-ER.retention.sequence.fusion.under.the.
control.of.the.banana.ethylene.forming.enzyme.promoter,.Sunil-Kumar.et.al..success-
fully.produced.antibody-reactive.antigen.in.banana.leaves.and.fruits. 206 .Unfortunately,.
antigen.levels.in.banana.fruit.were.very.low.compared.to.antigen.levels.achieved.in.
several.previously.described.annual.plant.systems.(1.ng/g.vs..16.μg/g.fresh.weight.in.
potato.tuber),.precluding.immunogenicity.testing.and.the.use.of.these.bananas.for.oral.
vaccination.

CONCLUSIONS
The.high.value.of.fruit.and.nut.crops.and.their.increasing.dietary.importance.due.to.
their. unique. nutritional. and. disease-preventing. attributes. has. focused. attention. on.
genetic.strategies.to.solve.production.limitations..The.technology.to.produce.trans-
genic. trees. is. relatively. mature,.especially. the.use.of.the. Agrobacterium -mediated.
transformation.process..However,.regeneration.of.transgenic.plants.continues.to.pose.
the.greatest.challenge.for.many.of.these.crops,.especially.Prunus..In.most.fruit.and.nut.
tree.species,.only.a.few.of.the.commercially.signiicant.phenotypes.have.been.exten-
sively.tested.in.the.ield..Viral.resistance.in.plum.and.papaya.has.been.deregulated,.
and.commercialized.in.the.case.of.papaya..Many.tree.crops.are.promising.candidates.
for.the.use.of.transgenic.technologies.to.prevent.disease.and.pest.infestation,.espe-
cially.through.the.use.of.Bt.insecticidal.proteins.that.target.lepidopteran.insect.pests..
Resistance. to. bacterial. pathogens. poses. the. greatest. challenge,. as. they. present. the.
greatest.threat.to.commercial.viability.in.many.perennial.crop.species..Substantial.
progress. has. been. made. toward. gaining. resistance. to. PD. in. grapevine. and. crown.
gall.disease.in.walnut..Many.fruit.quality.traits.have.also.been.manipulated,.primar-
ily. through. the. RNAi-mediated. regulation. of. ethylene. .biosynthesis. and/or. sorbitol.
biosynthesis,.where.the.phenotypes.have.been.documented.in.ield-grown.transgenic.
fruit..Many.interesting.transgenic.approaches.have.been.developed.for.other.quality.
traits.that.are.of.importance.to.consumers,.including.postharvest.storage.disorders,.
fruit. texture,. appearance,. sugar. and. lipid. composition,. and. allergenicity;. how-
ever,.these.phenotypes.remain.to.be.established.in.the.ield..With.the.exception.of.
papaya,.no.other.transgenic.fruit.variety.has.been.commercialized.and.the.technol-
ogy.development.toward.commercialization.for.scion.varieties.in.particular.has.been.
“soft-pedaled”. due. to. the. public. acceptance. issue.. Perhaps. the. greatest. immediate.
promise.lies.in.the.potential.for.commercialization.of.transgenic.rootstocks,.as.they.
can.provide.resistance.to.disease,.pest,.and.environmental.issues.while.sustaining.the.
production.of.a.wild-type.fruit.crop.from.the.grafted.(non-transgenic).scion.

REFERENCES
.

1.. Rieger,.M.,. Introduction to Fruit Crops ,.Food.Products.Press,.New.York,.p..462,.2006.

. 2.. FAOStat..http://faostat.fao.org/,.2008,.Accessed.on.March.3,.2010.

. 3.. Gomez-Lim,.M..A..and.Litz,.R..E.,.Genetic.transformation.of.perennial.tropical.fruits,.

In Vitro Cell. Dev. Biol. Plant ,.40,.442,.2004.