Identification and Functional Analysis of Two Mitoferrins, CsMIT1 and CsMIT2, Participating in Iron Homeostasis in Cucumber.

Mitochondria are one of the major iron sinks in plant cells. Mitochondrial iron accumulation involves the action of ferric reductase oxidases (FRO) and carriers located in the inner mitochondrial membrane. It has been suggested that among these transporters, mitoferrins (mitochondrial iron transporters, MITs) belonging to the mitochondrial carrier family (MCF) function as mitochondrial iron importers.

Cucumber Golgi protein CsMTP5 forms a Zn-transporting heterodimer with high molecular mass protein CsMTP12.

Heterodimeric complexes formed by members of the cation facilitator (CDF) family catalyse the import of Zn into the secretory pathway of yeast and vertebrate cells. Orthologous proteins AtMTP5 and AtMTP12 from Arabidopsis have also been shown to form a heterodimeric complex at the Golgi compartment of plant cells that possibly transport Zn. In this study we show that cucumber proteins CsMTP5 and CsMTP12 form a functional heterodimer that is involved in the loading of Zn into the ER lumen under low Zn, and not in the detoxification of yeast from Zn excess through vesicle-mediated exocytosis.

Metal tolerance protein MTP6 affects mitochondrial iron and manganese homeostasis in cucumber.

Members of the cation diffusion facilitator (CDF) family have been identified in all kingdoms of life. They have been divided into three subgroups, namely Zn-CDF, Fe/Zn-CDF, and Mn-CDF, based on their putative specificity to transported metal ions. The plant metal tolerance protein 6 (MTP6) proteins fall into the Fe/Zn-CDF subgroup; however, their function in iron/zinc transport has not yet been confirmed.

Cucumber metal tolerance protein 7 (CsMTP7) is involved in the accumulation of Fe in mitochondria under Fe excess.

The plant metal tolerance protein family (MTP) includes 12 members that have been classified into three phylogenetically different subgroups - Zn-cation diffusion facilitator (CDF), Fe/Zn-CDF and Mn-CDF - based on their putative metal specificity. To date, only members belonging to the Zn-CDF or Mn-CDF group have been characterized functionally. The plant Fe/Zn-CDF subgroup includes two proteins, MTP6 and MTP7, but their function and metal specificity have not been confirmed.

[Characterization of the proteins involved in the transport and storage of iron in plants].

Iron is a transient metal essential for the proper growth and development of plants because as a component of the enzymes with a wide redox potential, iron contributes to the key cellular processes. During evolution, plants have developed a wide range of molecular mechanisms for the efficient control of iron homeostasis within their cells, tissues and organs. These include membrane proteins involved in the uptake, long-distance transport and intracellular distribution of iron as well as the iron-storing and iron-chelating proteins, that are involved in the protection of the plant cells from iron excess and/or ensure the proper growth and development of plants under Fe deficiency.