title: iTRAQ analysis reveals mechanisms of growth defects due to excess zinc in Arabidopsis.
abstract: The micronutrient zinc is essential for all living organisms, but it is toxic at high concentrations. Here, to understand the effects of excess zinc on plant cells, we performed an iTRAQ (for isobaric tags for relative and absolute quantification)-based quantitative proteomics approach to analyze microsomal proteins from Arabidopsis (Arabidopsis thaliana) roots. Our approach was sensitive enough to identify 521 proteins, including several membrane proteins. Among them, IRT1, an iron and zinc transporter, and FRO2, a ferric-chelate reductase, increased greatly in response to excess zinc. The expression of these two genes has been previously reported to increase under iron-deficient conditions. Indeed, the concentration of iron was significantly decreased in roots and shoots under excess zinc. Also, seven subunits of the vacuolar H(+)-ATPase (V-ATPase), a proton pump on the tonoplast and endosome, were identified, and three of them decreased significantly in response to excess zinc. In addition, excess zinc in the wild type decreased V-ATPase activity and length of roots and cells to levels comparable to those of the untreated de-etiolated3-1 mutant, which bears a mutation in V-ATPase subunit C. Interestingly, excess zinc led to the formation of branched and abnormally shaped root hairs, a phenotype that correlates with decreased levels of proteins of several root hair-defective mutants. Our results point out mechanisms of growth defects caused by excess zinc in which cross talk between iron and zinc homeostasis and V-ATPase activity might play a central role.
authors.affiliation: Plant Science Education Unit, Nara Institute of Science and Technology, Ikoma 630-0192, Japan. fukao@bs.naist.jp
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Fukao
authors.forename: Ali
authors.initials: A
authors.lastname: Ferjani
authors.forename: Rie
authors.initials: R
authors.lastname: Tomioka
authors.forename: Nahoko
authors.initials: N
authors.lastname: Nagasaki
authors.forename: Rie
authors.initials: R
authors.lastname: Kurata
authors.forename: Yuka
authors.initials: Y
authors.lastname: Nishimori
authors.forename: Masayuki
authors.initials: M
authors.lastname: Fujiwara
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Maeshima
mesh_terms: D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism; D049108:Cell Enlargement; D038181:FMN Reductase / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D000090463:Iron Deficiencies; D016254:Mutagenesis, Insertional; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D020543:Proteome / Q000032:analysis; D040901:Proteomics / Q000379:methods*; D018749:RNA, Plant / Q000235:genetics; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology*
chemical_list: D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; C099651:IRT1 protein, Arabidopsis; D020543:Proteome; D018749:RNA, Plant; D038181:FMN Reductase; C023903:ferric citrate iron reductase; D025262:Vacuolar Proton-Translocating ATPases; D015032:Zinc