Handling Copper: A Paradigm for the Mechanisms of Metal Ion Homeostasis - Environmental Contamination: Health Risks and Ecological Restoration - page 284

Chlamydomonas .is.a.highly.studied.unicellular,.lagellate,.green.alga..Cells.of.
Chlamydomonas .contain.one.large.chloroplast.that.has.similar.photosynthetic.
machinery.as.higher.plants..There.are.three.target.enzymes.that.require.cop-
per.for.proper.function.in. Chlamydomonas ,.cytochrome.oxidase,.plastocyanin,.
and.multicopper.oxidases.involved.in.iron.acquisition.(Merchant.et.al..2006)..
It.has.been.proposed.that.copper.reductases.work.in.concert.with.a.copper.
transporter.to.import.the.metal.into.cells..A.COPT1.transporter.protein.has.
been.identiied.in. Chlamydomonas .which.is.similar.to.the. Arabidopsis .COPT1.
(Hanikenne.et.al..2005)..In.addition,.this.organism.contains.three.different.
HMA.transporters.(HMA1,.HMA2,.and.HMA3)..The.HMA1.protein.is.simi-
lar.to.the. Arabidopsis .HMA1,.while.HMA2.and.HMA3.cluster.with.P 1B -type.
ATPases.that.are.copper.transporters,.such.as.RAN1.in.plants.(Hanikenne.
et.al..2005)..Although.copper.is.an.essential.micronutrient,.ion.transport.in.
this.organism.is.not.well.understood..Recently,.microarray.analysis.has.been.
implemented.to.investigate.gene.transcription.responses.to.external.copper.
concentrations.in. Chlamydomonas ..In.addition.to.genes.involved.in.metabolic.
processes,. stress-related. and. intracellular. proteolysis. genes. were. greatly.
affected.by.copper.concentrations.(Jamers.et.al..2006).
Copper Homeostasis in Higher Plants Using Arabidopsis as a Model
Arabidopsis . is. a. model. organism. for. plant. systems. that. is. widely. used. in.
genetic.and.molecular.investigations..Reasons.for.its.use.as.a.model.include,.
a. sequenced. genome,. short. life. cycle,. and. it. is. relatively. easy. to. cross. and.
mutate..Plants.are.complex,.multicellular.organisms.that.transport.essential.
micronutrients,.like.copper,.over.a.long.distance.through.organs.and.across.
several.membranes.before.they.reach.their.inal.destination.in.target.proteins.
Copper.enters.through.the.cell.membrane.from.the.apoplast.by.a.Ctr-like.
transporter.called.COPT1.(Kampfenkel.et.al..1995),.and.is.either.sequestered.
or.traficked.to.targets.by.copper.chaperones.(Figure.13.7)..The.COPT1.pro-
tein. and. its. four. homologs. are. expressed. in. stems,. lower,. leaf,. as. well. as.
root.tissue.(Sancenon.et.al..2003).and.COPT1.antisense.plants.show.abnor-
malities. in. pollen. formation. and. increased. root. length. (Sancenon. et. al..
2004)..This.analysis.suggests.that.COPT1.may.play.a.role.in.copper.uptake.
in.the.roots.from.surrounding.environment..Little.work.has.been.done.on.
the. other. proteins. in. the. COPT. family. with. localizations. of. proteins. and.
molecular.characterizations.of.mutants.pending.
Arabidopsis . contains. two. different. cytosolic. ATX-like. copper. chaperones,.
CCH. and. ATX1. (Himelblau. et. al.. 1998,. Puig. et. al.. 2007).. Both. proteins. are.
functional. homologs. of. the. yeast. ATX1. and. have. been. shown. to. interact.
with. the. P-type. ATPases,. RAN1. in. the. Golgi. membrane. (Puig. et. al.. 2007).
and.HMA5.in.the.plasma.membrane.(Andres-Colas.et.al..2006)..The.RAN1.
(responsive-to-antagonist1).transporter.is.a.homolog.of.the.yeast.Ccc2.pro-
tein.and.functions.to.translocate.copper.into.the.endomembrane.system.were.
it. is. required. for. ethylene. signaling. (Hirayama. et. al.. 1999,. Hirayama. and.