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A Root-Expressed Magnesium Transporter of the MRS2/MGT Gene Family in Arabidopsis thaliana Allows for Growth in Low-Mg²⁺ Environments^[W]

Michael Gebert^a, Karoline Meschenmoser^a, Soa Svidová^b, Julian Weghuber^b, Rudolf Schweyen^b,1, Karolin Eifler^a, Henning Lenz^a, Katrin Weyand^a and Volker Knoop^a,2

^a Institut für Zelluläre und Molekulare Botanik, Universität Bonn, D-53115 Bonn, Germany
^b Vienna Biocenter, Abteilung für Mikrobiologie und Genetik, A-1030 Wien, Austria

² Address correspondence to volker.knoop{at}uni-bonn.de.

The MRS2/MGT gene family in Arabidopsis thaliana belongs to the superfamily of CorA-MRS2-ALR-type membrane proteins. Proteins of this type are characterized by a GMN tripeptide motif (Gly-Met-Asn) at the end of the first of two C-terminal transmembrane domains and have been characterized as magnesium transporters. Using the recently established mag-fura-2 system allowing direct measurement of Mg²⁺ uptake into mitochondria of Saccharomyces cerevisiae, we find that all members of the Arabidopsis family complement the corresponding yeast mrs2 mutant. Highly different patterns of tissue-specific expression were observed for the MRS2/MGT family members in planta. Six of them are expressed in root tissues, indicating a possible involvement in plant magnesium supply and distribution after uptake from the soil substrate. Homozygous T-DNA insertion knockout lines were obtained for four members of the MRS2/MGT gene family. A strong, magnesium-dependent phenotype of growth retardation was found for mrs2-7 when Mg²⁺ concentrations were lowered to 50 µM in hydroponic cultures. Ectopic overexpression of MRS2-7 from the cauliflower mosaic virus 35S promoter results in complementation and increased biomass accumulation. Green fluorescent protein reporter gene fusions indicate a location of MRS2-7 in the endomembrane system. Hence, contrary to what is frequently found in analyses of plant gene families, a single gene family member knockout results in a strong, environmentally dependent phenotype.