Genetic Engineering of Grapevine and Progress toward Commercial Deployment - Transgenic Horticultural Crops: Challenges and Opportunities - page 325

reinserted.into.the.plant..Such.genes.often.modify.metabolism.in.a.manner.similar.to.
natural.or.induced.mutations.without.causing.genetic.contamination. 49 .The.improve-
ments.achieved.via.use.of.such.endogenous.genes.should.be.qualitatively.similar.to.
those.obtained.via.traditional.breeding.approaches,.but.signiicantly.more.precise,.
due.to.the.ability.to.overexpress.desired.proteins,.both.temporally.and.spatially..In.
addition,.endogenous/homologous.transgenes.can.be.deined.and.regulated.differen-
tially.as.compared.to.use.of.foreign.transgenes.for.crop.genetic.engineering. 50 .It.is.
possible.that.transgenic.modiication.of.native.genes.tends.to.inherently.balance.the.
selection.process.and.maintain.natural.variance. 49
PR Proteins
A.number.of.genes,.commonly.known.as.PR.(pathogenesis.related).protein.genes,.
have. been. cloned. from. and. expressed. in. the. plant. species. from. which. they. were.
cloned.. They. have. been. grouped. (PR. 1-PR. 5). based. on. their. structure. and. mode.
of.action. 51 .A.number.of.PR.proteins.exhibit.antifungal.properties,.which.variously.
cause.inhibition.of.fungal.cell.wall.synthesis.and/or.a.disruption.in.cell.wall.struc-
ture.leading.to.cell.lysis. 52 .PR.proteins.are.classiied.into.different.groups.including.
cysteine.rich.antimicrobial.peptides, 53-57 .glucanases.and.chitinases, 52 .chitin.binding.
proteins 53,58 .and.thaumatin.like.(TL).proteins. 52
The.PR.5,.or.TL.proteins,.share.signiicant.amino.acid.homology.to.thaumatin. 52 .
TL.proteins.inhibit.a.wide.range.of.plant.pathogens.in.vitro 52 .and.have.been.cloned.
from.several.plant.species. 59-62 .TL.proteins.are.known.to.be.differentially.expressed.
in. reproductive. tissues. such. as. pistils. and. ripening. fruits. 63-66 . The. University. of.
Florida/Institute.of.Food.and.Agricultural.Sciences.(UF/IFAS).grape.biotechnology.
laboratory.cloned. V. vinifera .thaumatin-like.protein.(VVTL-1).gene.from.grapevines.
derived.from.embryogenic.cultures.that.were.subjected.to.in.vitro.selection.with.the.
culture. iltrate. of. Elsinoe ampelina ,. the. causal. agent. of. grapevine. anthracnose. 67 .
Protein.produced.from.VVTL-1.signiicantly.inhibited. E. ampelina .spore.germina-
tion.and.hyphal.growth.in.vitro..Plants.regenerated.from.in.vitro-selected.cultures.
similarly.inhibited.fungal.growth.in.leaf.assays..Similar.results.have.been.obtained.
with.VVTL-2.cloned.from.grape,.which.was.expressed.in.leaves.and.ripening.berries.
in.response.to.powdery.mildew.infection 68,69 .and.exhibited.antifungal.properties. 70
Seed Proteins
Seeds.contain.a.wide.array.of.antimicrobial.compounds.that.can.be.expressed.in.a.
constitutive.or.inducible.manner. 71 .Although.2S.albumins.are.generally.considered.
as. storage. proteins,. they. also. inhibit. growth. of. pathogenic. fungi. in. part. by. per-
meabilization.of.hyphal.plasmalemma. 72,73 .2S.albumin.genes.have.been.cloned.from.
sunlower, 74 .Brazil.nut, 75 .grape, 76 .and.other.crop.plants..In.grape,.we.have.cloned.the.
entire.2S.albumin.gene.along.with.the.coding.sequence.and.promoter.elements 76 .and.
we.are.evaluating.its.expression.(Li.et.al.,.unpublished.data).
Stilbene Synthase
Phytoalexins. are. low. molecular. weight. antimicrobial. compounds. that. are. synthe-
sized.by.and.accumulate.in.plants.in.response.to.biotic.and.abiotic.stresses..Stilbenes.
and.their.derivatives.have.been.regarded.as.phytoalexins.that.contribute.to.defense.