Abstract
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. Here, we characterized the MTP6 protein from cucumber, Cucumis sativus. When expressed in yeast and in protoplasts isolated from Arabidopsis cells, CsMTP6 localized in mitochondria and contributed to the efflux of Fe and Mn from these organelles. Immunolocalization of CsMTP6 in cucumber membranes confirmed this association with mitochondria. Root expression and protein levels of CsMTP6 were significantly up-regulated in conditions of Fe deficiency and excess, but were not affected by Mn availability. These results indicate that MTP6 proteins contribute to the distribution of Fe and Mn between the cytosol and mitochondria of plant cells, and are regulated by Fe to maintain mitochondrial and cytosolic iron homeostasis under varying conditions of Fe availability.
Highlights
Iron plays an essential role in many housekeeping cellular functions, including respiration, photosynthesis, Fe-S cluster assembly, and heme synthesis, but it can be highly reactive and toxic as a catalyst of the Fenton reaction when present in excess (Winterbourn, 1995; Briat et al, 2010)
Group 6 containing the metal tolerance protein 6 (MTP6) proteins has been classified in the Fe/ Zn-cation diffusion facilitator (CDF) group, including bacterial FieF-like and WmFieF-like proteins and the fungal MMT-like proteins, which are involved in Fe transport (Li and Kaplan, 1997; Grünberg et al, 2001; Grass et al, 2005; Li et al, 2014)
CsMTP6 was differentially expressed in all the vegetative organs, with the lowest expression level in the hypocotyls (Fig. S1, Dataset S1 at Dryad). cDNA prepared from the bulk sample of roots was used to amplify the full cDNAs of CsMTP6 for the subsequent analysis of CsMTP6 function and localization in yeast and Arabidopsis protoplasts
Summary
Iron plays an essential role in many housekeeping cellular functions, including respiration, photosynthesis, Fe-S cluster assembly, and heme synthesis, but it can be highly reactive and toxic as a catalyst of the Fenton reaction when present in excess (Winterbourn, 1995; Briat et al, 2010).
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