title: Long-distance root-to-shoot transport of phytochelatins and cadmium in Arabidopsis.
abstract: Phytochelatin synthases (PCS) mediate cellular heavy-metal resistance in plants, fungi, and worms. However, phytochelatins (PCs) are generally considered to function as intracellular heavy-metal detoxification mechanisms, and whether long-distance transport of PCs occurs during heavy-metal detoxification remains unknown. Here, wheat TaPCS1 cDNA expression was either targeted to Arabidopsis roots with the Arabidopsis alcohol dehydrogenase (Adh) promoter (Adh::TaPCS1/cad1-3) or ectopically expressed with the cauliflower mosaic virus 35S promoter (35S::TaPCS1/cad1-3) in the PC-deficient mutant cad1-3. Adh::TaPCS1/cad1-3 and 35S::TaPCS1/cad1-3 complemented the cadmium, mercury, and arsenic sensitivities of the cad1-3 mutant. Northern blot, RT-PCR, and Western blot analyses showed Adh promoter-driven TaPCS1 expression only in roots and thus demonstrated lack of long-distance TaPCS1 mRNA and protein transport in plants. Fluorescence HPLC analyses showed that under Cd2+ stress, no PCs were detectable in cad1-3. However, in Adh::TaPCS1/cad1-3 plants, PCs were detected in roots and in rosette leaves and stems. Inductively coupled plasma atomic emission spectrometer analyses showed that either root-specific or ectopic expression of TaPCS1 significantly enhanced long-distance Cd2+ transport into stems and rosette leaves. Unexpectedly, transgenic expression of TaPCS1 reduced Cd2+ accumulation in roots compared with cad1-3. The reduced Cd2+ accumulation in roots and enhanced root-to-shoot Cd2+ transport in transgenic plants were abrogated by l-buthionine sulfoximine. The presented findings show that (i) transgenic expression of TaPCS1 suppresses the heavy-metal sensitivity of cad1-3, (ii) PCs can be transported from roots to shoots, and (iii) transgenic expression of the TaPCS1 gene increases long-distance root-to-shoot Cd2+ transport and reduces Cd2+ accumulation in roots.
authors.affiliation: Division of Biological Sciences and Center for Molecular Genetics, Cell and Developmental Biology Section, University of California at San Diego, La Jolla, CA 92093-0116, USA.
authors.forename: Ji-Ming
authors.initials: JM
authors.lastname: Gong
authors.forename: David A
authors.initials: DA
authors.lastname: Lee
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D019881:Aminoacyltransferases / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D002104:Cadmium / Q000493:pharmacokinetics* / Q000633:toxicity; D004351:Drug Resistance; D017343:Genes, Plant; D005978:Glutathione; D008667:Metalloproteins / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation; D054811:Phytochelatins; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D030821:Plants, Genetically Modified
chemical_list: D008667:Metalloproteins; D002104:Cadmium; D019328:Buthionine Sulfoximine; D054811:Phytochelatins; D019881:Aminoacyltransferases; C093784:glutathione gamma-glutamylcysteinyltransferase; D005978:Glutathione