Plant Selenium Metabolism: Genetic Manipulation, Phytotechnological Applications, and Ecological Implications - Environmental Contamination: Health Risks and Ecological Restoration - page 302

in.agreement.with.the.laboratory.results..Plant.growth.was.the.same.for.all.
plant.types.in.this.experiment..Two.ield.experiments.were.carried.out.on.
Se.(selenate)-contaminated.sediment.in.the.San.Joaquin.Valley.(California).
by. Bañuelos. et. al.. (2005,. 2007).. The. APS. transgenics. accumulated. Se. to.
fourfold. higher. levels. than. wild-type. B. juncea ,. and. cpSL. and. SMT. trans-
genics.showed.twofold.higher.Se.accumulation.than.wild-type. B. juncea ,.all.
in.agreement.with.earlier.laboratory.experiments..Biomass.production.was.
comparable. for. the. different. plant. types.. Thus,. in. the. ield. as. well. as. the.
lab,.the.various.transgenics.showed.enhanced.Se.accumulation,.volatiliza-
tion,.and/or.tolerance,.all.promising.traits.for.use.in.phytoremediation.or.as.
Se-fortiied.foods.
NewInsightintoSeToleranceandAccumulation
MechanismsfromIntegratedGenomic,
Genetic,andBiochemicalApproaches
In.order.to.obtain.new.insight.into.key.genes.that.control.Se.uptake,.hyperac-
cumulation,.and. volatilization , . several.studies.were. done.in.the. past.years.
using.either.model.plant.species.or.hyperaccumulators..First,.a.comparative.
study.was.performed.using.recombinant.inbred.lines.(RIL).of.model.species.
A. thaliana ..Several.quantitative.trait.loci.(QTL).were.identiied.that.cosegre-
gated. with. the. higher. selenate. tolerance. in. accession. Columbia. compared.
with.accession.Landsberg.erecta.(Zhang.et.al..2006a)..Genes.in.the.identiied.
QTL.regions.include.a.homologue.of.SeCys.methyl.transferase.(SMT),.ATP.
sulfurylase,.and.SAT..The.results.from.the.QTL.study.strongly.suggested.that.
tolerance. to. selenate. and.selenite. is. controlled. by. different. loci.. In. another.
study,.tolerance.to.and.accumulation.of.Se.were.found.to.not.be.correlated.
in.a.study.comparing.19.different.ecotypes.of. Arabidopsis .with.variable.toler-
ance.to.Se.(Zhang.et.al..2006b)..Based.on.these.results,.it.should.be.possible.
to.breed.plants.that.both.accumulate.and.tolerate.Se.well.
In.another.approach.to.identify.key.genes.modulating.the.Se.response,.a.
transcriptome.study.was.performed.on.plants.grown.on.selenate.and.con-
trol. media. for. 10. days. (Van. Hoewyk. et. al.. 2008).. Genes. involved. in. ethyl-
ene.and.jasmonic.acid.(JA).pathways.were.upregulated.by.Se..Furthermore,.
Arabidopsis . mutants. with. a. defect. in. genes. involved. in. ethylene. synthesis.
(acs6),.ethylene.signaling.(ein2-1.and.ein3-1),.and.JA.signaling.(jar1-1).showed.
reduced. tolerance. to. selenate,. and. overexpression. of. a. protein. involved. in.
ethylene.signaling.(ERF1).increased.selenate.resistance.(Van.Hoewyk.et.al..
2008)..A.similar.study.by.Tamaoki.et.al..(2008).also.implicated.the.involve-
ment.of.the.two.hormones.ethylene.and.JA.in.selenite.resistance.(Tamaoki.
et. al.. 2008). and. additionally. suggested. that. reactive. oxygen. species. (ROS).
may. have. a. signaling. role.. The. resistance. mechanism. appears. to. involve.