Zinc Transporter of Arabidopsis thaliana AtMTP1 is Localized to Vacuolar Membranes and Implicated in Zinc Homeostasis

Abstract

Cation diffusion facilitator (CDF) proteins belong to a family of heavy metal efflux transporters that might play an essential role in homeostasis and tolerance to metal ions. We investigated the subcellular localization of Arabidopsis thaliana AtMTP1, a member of the CDF family, and its physiological role in the tolerance to Zn using MTP1-deficient mutant plants. AtMTP1 was immunochemically detected as a 43 kDa protein in the vacuolar membrane fractioned by sucrose density gradient centrifugation. The expression level of AtMTP1 in suspension-cultured cells was not affected by the Zn concentration in the medium. When AtMTP1 fused with green fluorescent protein was transiently expressed in protoplasts prepared from Arabidopsis suspension-cultured cells, green fluorescence was clearly observed in the vacuolar membrane. A T-DNA insertion mutant line for AtMTP1 displays enhanced sensitivity to high Zn concentrations ranging from 200 to 500 microM, but not to Zn-deficient conditions. Mesophyll cells of the mtp1-1 mutant plants grown in the presence of 500 microM Zn were degraded, suggesting that Zn at high concentrations causes serious damage to leaves and that AtMTP1 plays a crucial role in preventing this damage in plants. Thus we propose that AtMTP1 is localized in the vacuolar membrane and is involved in sequestration of excess Zn in the cytoplasm into vacuoles to maintain Zn homeostasis.

Multidrug and Toxic Compound Extrusion-Type Transporters Implicated in Vacuolar Sequestration of Nicotine in Tobacco Roots

“…Standard procedures (Lieberherr et al, 2005) and the manufacturer's protocol (Amersham Biosciences) were used for purification. Antisera against P-ATPase ( Kobae et al, 2004), V-ATPase (Kobae et al, 2004), and BiP (Hö fte and Chrispeels, 1992) were used, respectively, as markers for the plasma membrane, tonoplast, and endoplasmic reticulum.…”

Quantitative detection of changes in the leaf‐mesophyll tonoplast proteome in dependency of a cadmium exposure of barley (Hordeum vulgare L.) plants

“…Indeed, Fe 2+ importers as well 4 as exporters have been identified. For Zn 2+ only the importer, MTP1, has been described [8,12,13]. It is interesting to note that Arabidopsis halleri, a typical Zn hyperaccumulator, has a constitutive high expression of a MTP1 homologue [14].…”

Isolation of Zn-responsive genes from two accessions of the hyperaccumulator plant Thlaspi caerulescens

“…The T. caerulescens ZTP1 (Assunção et al 2001) is highly homologous to Arabidopsis thaliana MTP1 (formerly ZAT1), a member of the cation diVusion facilitator family of transporters involved in vacuolar Zn sequestration (van der Zaal et al 1999;Kobae et al 2004). The ZTP1 gene is more highly expressed in the roots and shoots of a Zn-tolerant T. caerulescens accession, suggesting that this gene may contribute to Zn tolerance (Assunção et al 2001).…”