Magnesium transporter AtMGT9 is essential for pollen development in Arabidopsis

Abstract

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.

MNR2 Regulates Intracellular Magnesium Storage in Saccharomyces cerevisiae

“…Most plant genomes encode multiple MIT proteins (Schock et al 2000;Li et al 2001). The Arabidopsis plasma membrane protein AtMGT1 (Li et al 2001), the chloroplast inner membrane protein AtMrs2-11 (Drummond et al 2006), and the mitochon-drial protein AtMgt5 (Chen et al 2009) have all been shown to play important roles in Mg homeostasis, but the function of many other members of this large gene family remains unknown. The identification of a functional homolog of Mnr2 in plants would further advance our understanding of Mg homeostasis in higher eukaryotes as well as provide a potentially useful tool to manipulate the nutrient content of economically important species.…”

Fertility control: the role of magnesium transporters in pollen development

“…The story became even more fascinating when Chen et al [3] described a second Mg 2+ transporter, AtMGT9, which also affected pollen viability. AtMGT9 supported the growth of the bacterial MM281 mutant at 500 µM Mg 2+ , but not at 10 µM Mg 2+ , reminiscent of a low-affinity transporter.…”

“…As with AtMGT5, disruption of AtMGT9 led to pollen abortion, and only hemizygous mutants survived. Crossing experiments proved that the mutated atmgt9 allele could not be transmitted through the pollen due to lack of fertility [3].…”

“…The works by Luan and co-workers [2,3] show a tight connection between Mg 2+ transporter function and pollen development for the first time, although we do not know in detail how the two transporters sustain pollen formation and thus fertility. One model supposes that both proteins are located in mitochondria (though the localization of AtMGT9 still has to be investigated) but function independently to contribute to mitochondrial Mg 2+ homeostasis.…”

“…Surprisingly, however, the molecular mechanisms underlying these processes in higher plants are still largely unknown. Recently, two reports [2,3] disclosed functions of two Mg 2+ transporters in pollen development. Pollen grains are the male gametes in flowering plants.…”