The Arabidopsis Mg Transporter, MRS2-4, is Essential for Mg Homeostasis Under Both Low and High Mg Conditions.

Magnesium (Mg) is an essential macronutrient, functioning as both a cofactor of many enzymes and as a component of Chl. Mg is abundant in plants; however, further investigation of the Mg transporters involved in Mg uptake and distribution is needed. Here, we isolated anArabidopsis thalianamutant sensitive to high calcium (Ca) conditions without Mg supplementation. The causal gene of the mutant encodes MRS2-4, an Mg transporter.MRS2-4single mutants exhibited growth defects under low Mg conditions, whereas anMRS2-4andMRS2-7double mutant exhibited growth defects even under normal Mg concentrations. Under normal Mg conditions, the Mg concentration of theMRS2-4mutant was lower than that of the wild type. The transcriptome profiles ofmrs2-4-1mutants under normal conditions were similar to those of wild-type plants grown under low Mg conditions. In addition, bothmrs2-4andmrs2-7mutants were sensitive to high levels of Mg. These results indicate that both MRS2-4 and MRS2-7 are essential for Mg homeostasis, even under normal and high Mg conditions. MRS2-4-green fluorescent protein (GFP) was mainly detected in the endoplasmic reticulum. These results indicate that these two MRS2 transporter genes are essential for the ability to adapt to a wide range of environmental Mg concentrations.

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