Transgenic Fruit Crops in Europe - Transgenic Horticultural Crops: Challenges and Opportunities - page 138

expensive. 4 .The.production.of.a.new.apple.cultivar.takes.at.least.15-20.years.and.
can.cost.in.the.range.of.€400,000.(Ken.Tobutt,.personal.communication.cited.in.
Fenning.and.Gershenzon 40 )..The.breeding.effort.is.mostly.hampered.by.the.long.
juvenile.phase.in.which.plants.are.not.able.to.lower.and.fruit..In.contrast.to.annual.
plants.which.lower.within.a.few.months,.juvenility.in.tree.species.can.last.5-40.
or.more.years. 4 .A.full.evaluation.of.a.progeny,.the.selection.of.the.best.seedlings.
and.therefore.all.further.breeding.activities.must.wait.until.the.plants.complete.the.
juvenile. phase.. Therefore,. shortening. the. juvenile. phase. is. always. an. important.
breeding.objective.for.fruit.crops..In.recent.years.much.effort.has.been.made.using.
biotechnological.methods..Leandro.Pena.and.coworkers.were.the.irst.to.describe.
the.successful.induction.of.early.lowering.in.a.fruit.tree.species.after.overexpres-
sion.of.the.lower.inducing.genes. LFY .and. AP1 .from. Arabidopsis thaliana . 41 .Since.
that.time.several.studies.on.different.fruit.crop.species.using.different.genes.have.
been. published. which. were. focused. on. the. reduction. of. the. juvenile. phase. (for.
review.see.Hanke.et.al. 42 )..However,.recently.Flachowsky.et.al. 4 .were.the.irst.to.
report.that.transgenic.early.lowering.apple.plants.were.successfully.used.for.prac-
tical.breeding.(Figure.5.5).
Transgenic.apple.plants.overexpressing.the. BpMADS4 .gene.of.silver.birch 43 .were.
pollinated. with. pollen. of. the. apple. wild. species. M. fusca .. Transgenic. seedlings.
lowered. within. the. irst. season. (Figure. 5.6).. They. were. pollinated. with. pollen. of.
the.apple.cultivar.'Topaz'.and.the.irst.fruits.were.harvested.in.the.end.of.the.irst.
growing.season. 4 .This.work.demonstrated.that.one.crossbred.generation.per.year.is.
feasible.and.represents.a.dream.come.true.for.breeders..Several.scientiic.groups.in.
Europe.are.currently.evaluating.this.system..However,.the.GM.apple.plants.used.in.
this.study.were.not.optimal..The.transgenic.plants.constitutively.overexpressing.the.
BpMADS4 .gene.are.often.malformed.and.the.fruit.yield.and.seed.set.is.very.low. 4 .
Therefore,.new.plants.expressing.the.gene.driven.by.an.inducible.promoter.are.under.
development.
d evelopment of a r apId a SSay for G ene f unctIon a nalySIS
Functional. genome. analysis. in. fruit. crops,. especially. for. genes. expressed. in. the.
fruit,. is. often. very. laborious.. Genes. to. be. characterized. must. either. be. overex-
pressed. or. silenced. in. transgenic. plants.. The. production. of. stably. transformed.
plants.is.time.consuming. and.expensive..A.full. evaluation.of.the.effects.coming.
from.the.transgene.is.not.possible.before.the.plant.enters.the.adult.phase,.and.this.
can. sometimes. take. up. several. years.. Much. more. complicated. is. the. character-
ization. of. genes,. which. are. members. of. a. multigene. family.. Several. transgenic.
lines. for. each. gene. are. necessary.. This. requires. time,. space,. and. the. associated.
expenses.. Recently. an. ingenious. method. was. described. by. Hoffmann. et. al. 44 . on.
strawberry,. which. is. based. on. transient. gene. silencing. through. the. iniltration.
of. Agrobacterium tumefaciens . carrying. an. engineered. plasmid. into. ripening.
fruits..Young.fruits,.which.were.still.attached.to.the.plants,.were.injected.with.an.
Agrobacterium .suspension.by.using.a.sterile.1.mL.hypodermic.syringe..The.bac-
teria. containing. a. hairpin. gene. construct. were.evenly. distributed. throughout. the.
entire.fruit..Using.this.method.it.was.possible.to.silence.the. FaCHS .gene.in.nearly.