A Root-Expressed Magnesium Transporter of theMRS2/MGTGene Family inArabidopsis thalianaAllows for Growth in Low-Mg2+ Environments

Abstract

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 Mg 2+ 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 Mg 2+ concentrations were lowered to 50 mM 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.

Two Distinct Families of Protein Kinases Are Required for Plant Growth under High External Mg2+ Concentrations in Arabidopsis

“…Therefore, it is essential for photosynthesis. Recent studies have revealed that several mitochondrial RNA splicing2 (MRS2)/magnesium transport (MGT) proteins, which are structurally homologous to bacterial Co 2+ resistance A (CorA) proteins and ALUMINUM RESISTANCE1 (ALR1), ALR2, and MRS2 in yeast, play an important role in Mg 2+ transport and plant growth under low external Mg 2+ conditions (Gebert et al, 2009;Lenz et al, 2013;Mao et al, 2014). However, it remains largely unknown how plants maintain cellular Mg 2+ homeostasis under high external Mg 2+ conditions.…”

Root-Specific Reduction of Cytokinin Causes Enhanced Root Growth, Drought Tolerance, and Leaf Mineral Enrichment in Arabidopsis and Tobacco

“…Mg 2+ ions are transported in plants by proteins of the MRS2/ MGT family (Gebert et al, 2009). qRT-PCR analysis revealed that none of the eight analyzed MRS2/MGT genes showed a significantly and consistently increased expression level in roots of transgenic plants when compared with wild-type controls (see (A) Summary of changes in the concentrations of all analyzed elements in plants grown under different conditions.…”

ArabidopsisTransporter MGT6 Mediates Magnesium Uptake and Is Required for Growth under Magnesium Limitation

“…Members of the MGT family are expressed in a broad range of plant tissues (Li et al, 2001Mao et al, 2008;Chen et al, 2009;Gebert et al, 2009), and the proteins are located to the plasma membrane or in intracellular organelles, including mitochondria, plastid, and tonoplast (Li et al, 2001Drummond et al, 2006;Gebert et al, 2009;Conn et al, 2011), indicating their roles in Mg 2+ transport in and out of the cell and in exchange among the compartments of the cell.…”

“…We refer to this family as MGT for simplicity unless studies using different terms are discussed. The Mg 2+ transport activities of several MGTs have been characterized in heterologous systems, including bacteria or yeast mutants lacking Mg 2+ transport capacity (Schock et al, 2000;Li et al, 2001Li et al, , 2008Mao et al, 2008;Chen et al, 2009;Gebert et al, 2009). In these systems, members of the MGT family vary in their affinities for Mg 2+ transport, including highaffinity (MGT1 and MGT10), low-affinity (MGT7 and MGT9), and dual-affinity (MGT5) members (Schock et al, 2000;Li et al, 2001Li et al, , 2008Drummond et al, 2006;Mao et al, 2008;Chen et al, 2009;Gebert et al, 2009).…”