Research On The Function Of A Magnesium Transporter Gene AtMGT7

Magnesium(Mg2+) is the most abundant divalent cation in plant cells and plays a critical role in many physiological processes. The absorption, transportation and assimilation of magnesium are strictly controlled in the tissues and cells.So far, the transport mechanism of magnesium is well known in the bacteria. But it is less understood about the absorption and transportation of magnesium in plant from the molecular levels.In 2001,Li et al identified a putative Mg2+transport gene family(AtMGT) which was a little homology to the CorA of bacteria and MRS2 of yeast by sequence analysis. In our research, we have cloned a AtMGT7 gene by reverse transcription-polymerase chain (RT-PCR). Interestingly, this gene encodes two mRNAs transcripts resulted from alternative splicing variants, designated AtMGT7a and AtMGT7b. AtMGT7a contains 1158 base pairs of nucleotides in the open-reading-frame (ORF), encoding a putative protein of 386 amino acid residues,whereas AtMGT7b contains 1113 nucleotides of ORF, encoding a putative truncated protein of 371 amino acid residues.Gene expression analysis disclosed that the two mRNA variants were expressed with different patterns.AtMGT7a mRNA was widely expressed in all organs,but AtMGT7b was appeared only in root and flower tissues.Furthermore,we localized AtMGT7a to the plasma membrane,whereas AtMGT7b could localize plasma membrane or Functional complementation indicates that AtMGT7a could complement a bacterial mutant strain deficient in Mg2+uptake, while AtMGT7b did not. Furthermore,The 63Ni2+ tracer analysis in the bacterial model showed that AtMGT7a mediates low-affinity transporter of Mg2+, whereas AtMGT7b may be involved in the transport Cu2+ or Cd2+.The patch-clamp technique was used to measure whole-cell ion currents in the HEK293 cell,the HEK293 cell over-expressing AtMGT7a and AtMGT7b.with 50mM Mg2+ bathing sulution, The current in HEk293+AtMGT7a cell averaged-286±46pA. The currents in the HEk293+AtMGT7b cell and HEK293 is more than six-fold smaller. We conclude that AtMGT7a may functionas a magnesium ion channel in HEk cell.Compared to wild type, the color of the leaf in the mutant of AtMGT7 is phenotypically lighter under the Mg2+-dificiency condition. We further examined the content of Chlorophyll and magnesium. The content of Chlorophyll and magnesium in the mutant are obviously lower than the wild type.In short, this study has identified from a higher plant the first low-affinity magnesium transporter encoded by AtMGTJ gene. Connected with the high-affinity magnesium transporter, such as AtMGT1,it presented biological diversity of magnesium transporter. Additionally, the lage magnitude of the Mg2+-depedent currents in HEK293 cell suggests that AtMGT7a could function as an ion channel in plant.