A high molecular mass zinc transporter MTP12 forms a functional heteromeric complex with MTP5 in the Golgi in Arabidopsis thaliana

Zinc (Zn) is an essential micronutrient required for plant growth and development. In Arabidopsis thaliana, several families of Zn transporters engaged in Zn import, export and intracellular compartmentalization play important roles in Zn homeostasis. We describe a novel Zn transporter, A. thaliana metal tolerance protein 12 (AtMTP12), which belongs to the cation diffusion facilitator family. AtMTP12 is predicted to consist of 798 amino acids and have 14 transmembrane segments. The expression of AtMTP12 in suspension-cultured cells was not affected by Zn deficiency or excess. Heterologous expression in a mutant of budding yeast (Saccharomyces cerevisiae) that lacks Msc2p, an orthologue of AtMTP12, revealed that AtMTP12 complements the growth phenotype of the msc2 mutant when AtMTP5t1, one of the splicing variants of AtMTP5, is coexpressed. Transient expression of AtMTP12-fused green fluorescent protein in A. thaliana mesophyll protoplasts demonstrated that AtMTP12 is localized to the Golgi apparatus. Moreover, AtMTP12 and AtMTP5t1 interact in the Golgi, as determined by a bimolecular fluorescence complementation assay. These results suggest that AtMTP12 forms a functional complex with AtMTP5t1 to transport Zn into the Golgi.