Transgenic Fruit and Nut Tree Crops Review - Transgenic Horticultural Crops: Challenges and Opportunities - page 11

Recently,. transgenic. grapevines. containing. xylem-targeted. effector. proteins.
like. polygalacturonase. inhibiting. protein. (PGIP). and/or. chimeric. antimicrobial.
proteins.have. been.obtained. 117-121 . The. use.of.PGIP.to.transform.grapevines.was.
based.on.the.knowledge.that. Xf .has.genes.that.encode.plant.cell.wall-degrading.
enzymes,. including. polygalacturonases. 117 . Five. PGIP. expression. constructs. were.
designed,.each.containing.different.signal.peptide.sequences.in.order.to.identify.
which. most. eficiently. localizes. PGIP. to. xylem. tissues,. as. well. as. which. pro-
vides. the. best. distribution. of. PGIP. through. the. graft. union. into. untransformed.
scion.tissues. 120 .Chimeric.antimicrobial.protein.strategy.provides.a.protein-based.
therapeutic.that.targets.the.causative.agent.speciically.resulting.in.its.clearance,.
which. results. in. resistance. to. the. causative. agent.. Chimeric. proteins. have. two.
domains,. a. surface. binding. domain. and. a. clearance. domain. linked. by. a. lexible.
linker.such.that.both.components.can.act.independently. 120,121 .A.chimeric.antimi-
crobial. protein.was.designed.to. obtain.resistance. to.PD.that. contained.a.surface.
recognition. domain. (SRD). and. a. clearance. domain. (CD).. The. SRD. targeted. the.
Xf surface. protein. mopB,. highly. conserved. among.all. Xf . strains. and. believed. to.
be. unique. to. Xf 118 . linked. to. the. CD,. a. lytic. peptide. with. antimicrobial. activity.
against. Gram-negative. bacteria.. Transgenic. grapevines. expressing. PGIP. or. the.
chimeric. antimicrobial. protein. have. been. greenhouse. propagated. and. mechani-
cally.inoculated.with. Xf .to.validate.their.eficiency.against.PD;.the.results.obtained.
look.promising. 120 .Transgenic.grapevines.ield.trials.in.multiple.locations.started.
in.2010.
Xanthomonas
Citrus. canker. (CC). is. a. serious. endemic. disease. caused. by. Xanthomonas
citri . (syn. Xanthomonas campestris . pv.. citri . or. related. Xanthomonas campestris .
pv. aurantifolii ).. X. citri . affects. various. citrus. species. and. is. dispersed. by. wind-
blown. rain,. contaminated. equipment,. and. human. activity.. Canker. threatens. the.
.existence. of. citrus. industry,. affecting. leading. citrus. producers. from. Brazil. and.
Florida..Canker.symptoms.are.characterized.by.pustule-like.lesions.that.can.cover.
the.surfaces.of.leaves,.stems,.and.fruits..Such.lesions.later.become.corky.and.sur-
rounded. by. water-soaked. margins. with. a. yellow. halo. 122 .It. has. been. observed. that.
soon.after.infection, X. citri . simultaneously.suppresses. the. host.basal.defense. and.
induces.remarkable.changes.in.the.transcriptional.proiles.of.genes.associated.with.
cell.wall.remodeling,.cell.division.and.expansion,.vesicle.traficking.and.response.to.
the.hormones.auxin.and.gibberellin. 123-125
Genetic.transformation.has.been.used.in.citrus.cultivars.to.improve.CC.disease.
resistance.by.the.expression.of.the. Sarcophaga peregrine .sarcotoxin, 126 .the. atta-
cin E .antimicrobial.peptide.from. Tricloplusia ni , 127,128 .the. Xa21 .gene.from. Oryza
sativa , 129 .and.the.harpin.N.gene.( hrpN ).from. Erwinia amylovora . 130 .For.example,.
transgenic. Citrus sinensis . plants. expressing. hrpN . under. transcriptional. control.
of. a. pathogen. inducible. promoter. ( gst1 ). showed. up. to. 79%. reduction. in. suscep-
tibility.to.CC.compared.with.non-transgenic.plants. 130 .In.addition,.researchers.at.
Integrated.Plant.Genetics.have.developed.the.Disease.Block™.technology,.which.
consists. of. the. expression. of. a. recombinant. antibody. fragment. directed. against.
PthA,.an.effector.protein.associated.with.division,.enlargement,.and.death.of.the.