Poplar Metal Tolerance Protein 1 Confers Zinc Tolerance and Is an Oligomeric Vacuolar Zinc Transporter with an Essential Leucine Zipper Motif

Abstract

Cation diffusion facilitator (CDF) proteins are a recently discovered family of cation efflux transporters that might play an essential role in metal homeostasis and tolerance. Here, we describe the identification, characterization, and localization of PtdMTP1, a member of the CDF family from the hybrid poplar Populus trichocarpa ؋ Populus deltoides . PtdMTP1 is expressed constitutively and ubiquitously, although at low levels. Heterologous expression in yeast showed that PtdMTP1 was able to complement the hypersensitivity of mutant strains to Zn but not to other metals, including Cd, Co, Mn, and Ni. PtdMTP1 fused to green fluorescent protein localized to the vacuolar membrane both in yeast and in plant cells, consistent with a function of PtdMTP1 in zinc sequestration. Overexpression of PtdMTP1 in Arabidopsis confers Zn tolerance. We show that PtdMTP1, when expressed in yeast and Arabidopsis, forms homooligomers, a novel feature of CDF members. Oligomer formation is disrupted by reducing agents, indicating possible disulfide bridge formation. PtdMTP1 also contains a conserved Leu zipper motif. Although not necessary for oligomer formation, Leu residues within this motif are required for PtdMTP1 functional activity.

Transition metal transport

“…Blue colour denotes Zn-responsive genes with increased transcript levels upon Zn deficiency; orange colour denotes Zn homeostasis genes with mainly constitutive expression; green colour denotes genes that are more likely to be involved in the homeostasis of metal ions other than Zn. Superscripts denote the following microarray-based studies: [36].…”

Common Functions or Only Phylogenetically Related? The Large Family of PLAC8 Motif-Containing/PCR Genes

“…CAXs and some MTP transporters catalyze the transport of heavy metals across the vacuolar membrane and are essential for vacuolar sequestration. Increasing the expression of the tonoplast-localized MTP1 can enhance Zn resistance (Blaudez et al, 2003;Gustin et al, 2009;van der Zaal et al, 1999). In yeast, ATP-binding cassette (ABC) transporters sequester heavy metals into vacuoles.…”

A secretory pathway-localized cation diffusion facilitator confers plant manganese tolerance

“…The highly similar human Zn 2ϩ transporters Zn-T1, Zn-T2, and Zn-T3, for example, are targeted to plasma membrane, intracellular vesicles, and synaptic vesicles (23). There are 12 CDF members in the Arabidopsis genome (24). The Zn 2ϩ -transporting subfamily has been studied most extensively in plants (24)(25)(26)(27)(28)(29).…”