Although magnesium (Mg 2+ ) is the most abundant divalent cation in plant cells, little is known about the mechanism of Mg 2+ uptake by plant roots. Here, we report a key function of Magnesium Transport6 (MGT6)/Mitochondrial RNA Splicing2-4 in Mg 2+ uptake and low-Mg 2+ tolerance in Arabidopsis thaliana. MGT6 is expressed mainly in plant aerial tissues when Mg 2+ levels are high in the soil or growth medium. Its expression is highly induced in the roots during Mg 2+ deficiency, suggesting a role for MGT6 in response to the low-Mg 2+ status in roots. Silencing of MGT6 in transgenic plants by RNA interference (RNAi) resulted in growth retardation under the low-Mg 2+ condition, and the phenotype was restored to normal growth after RNAi plants were transferred to Mg 2+ -sufficient medium. RNAi plants contained lower levels of Mg 2+ compared with wild-type plants under low Mg 2+ but not under Mg 2+ -sufficient conditions. Further analysis indicated that MGT6 was localized in the plasma membrane and played a key role in Mg 2+ uptake by roots under Mg 2+ limitation. We conclude that MGT6 mediates Mg 2+ uptake in roots and is required for plant adaptation to a low-Mg 2+ environment.

Magnesium (Mg 2+ ) is abundant in plant cells and plays a critical role in many physiological processes. A 10-member gene family AtMGT (also known as AtMRS2) was identified in Arabidopsis, which belongs to a eukaryote subset of the CorA superfamily, functioning as Mg 2+ transporters. Some family members (AtMGT1 and AtMGT10) function as high-affinity Mg 2+ transporter and could complement bacterial mutant or yeast mutant lacking Mg 2+ transport capability. Here we report an AtMGT family member, AtMGT9, that functions as a low-affinity Mg 2+ transporter, and is essential for pollen development. The functional complementation assay in Salmonella mutant strain MM281 showed that AtMGT9 is capable of mediating Mg 2+ uptake in the sub-millimolar range of Mg 2+ . The AtMGT9 gene was expressed most strongly in mature anthers and was also detectable in vascular tissues of the leaves, and in young roots. Disruption of AtMGT9 gene expression resulted in abortion of half of the mature pollen grains in heterozygous mutant +/mgt9, and no homozygous mutant plant was obtained in the progeny of selfed +/mgt9 plants. Transgenic plants expressing AtMGT9 in these heterozygous plants can recover the pollen phenotype to the wild type. In addition, At-MGT9 RNAi transgenic plants also showed similar abortive pollen phenotype to mutant +/mgt9. Together, our results demonstrate that AtMGT9 functions as a low-affinity Mg 2+ transporter that plays a crucial role in male gametophyte development and male fertility.

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Excessive cadmium (Cd) accumulation in grains of rice (Oryza sativa L.) is a risk to food security. The transporters in the nodes of rice are involved in the distribution of mineral elements including toxic elements to different tissues such as grains. However, the mechanism of Cd accumulation in grains is largely unknown. Here, we report a node-expressed transporter gene, OsCCX2, a putative cation/calcium (Ca) exchanger, mediating Cd accumulation in the grains of rice. Knockout of OsCCX2 caused a remarkable reduction of Cd content in the grains. Further study showed that disruption of this gene led to a reduced root-to-shoot translocation ratio of Cd. Moreover, Cd distribution was also disturbed in different levels of internode and leaf. OsCCX2 is localized to plasma membrane, and OsCCX2 is mainly expressed in xylem region of vascular tissues at the nodes. OsCCX2 might function as an efflux transporter, responsible for Cd loading into xylem vessels. Therefore, our finding revealed a novel Cd transporter involved in grain Cd accumulation, possibly via a Ca transport pathway in the nodes of rice.

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