Recombinant Arabidopsis thaliana Magnesium transporter MRS2-7 (MRS2-7)
Description
Overview of MRS2-7
MRS2-7 is a magnesium (Mg²⁺) transporter encoded by the MRS2-7 gene in Arabidopsis thaliana. It belongs to the CorA-MRS2-ALR superfamily of membrane proteins, characterized by a conserved GMN (Gly-Met-Asn) tripeptide motif critical for Mg²⁺ transport . This protein is primarily expressed in root tissues and plays a vital role in Mg²⁺ uptake and homeostasis under low Mg²⁺ environments .
Key Features
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Gene Family: Part of the MRS2/MGT gene family, which includes 10 members in Arabidopsis.
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Subcellular Localization: Localized to the endomembrane system, including the endoplasmic reticulum (ER) .
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Transport Mechanism: Functions as an Mg²⁺ channel, mediating influx into organelles or cytoplasmic compartments .
Role in Magnesium Homeostasis
MRS2-7 is critical for maintaining Mg²⁺ balance under varying concentrations:
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Low Mg²⁺ Conditions:
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High Mg²⁺ Conditions:
Synergy with Other Transporters
MRS2-7 collaborates with MRS2-4 to regulate Mg²⁺ homeostasis:
Recombinant Protein Applications
Recombinant MRS2-7 is widely used in research for functional studies and antibody production:
Research Findings and Mechanistic Insights
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Mg²⁺ Uptake Efficiency:
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Tissue-Specific Expression:
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Regulatory Mechanisms:
Comparative Analysis with Homologs
MRS2-7 shares functional and structural similarities with other MRS2/MGT family members:
Product Specs
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Target Background
- MRS2-7 is the first identified low-affinity Mg2+ transporter from a higher plant. It is encoded by a gene with alternatively spliced transcripts resulting in proteins with distinct functions. [PMID: 19093971]
- Overexpression of MRS2-7 enhances biomass accumulation under magnesium-limiting conditions. [PMID: 19966073]
Q&A
What is MRS2-7 and what is its role in Arabidopsis thaliana?
MRS2-7 is a member of the MRS2/MGT gene family in Arabidopsis thaliana that functions as a magnesium transporter. This family belongs to the superfamily of CorA-MRS2-ALR-type membrane proteins characterized by a GMN tripeptide motif (Gly-Met-Asn) at the end of the first of two C-terminal transmembrane domains. MRS2-7 plays a crucial role in magnesium supply and distribution after uptake from the soil substrate. Unlike many other gene family member knockouts, a single gene knockout of MRS2-7 results in a strong, environmentally dependent phenotype, particularly showing growth retardation when magnesium concentrations are lowered to 50 μM in hydroponic cultures . This indicates that MRS2-7 has a specialized, non-redundant function in magnesium homeostasis within the plant.
Where is MRS2-7 expressed in Arabidopsis thaliana?
MRS2-7 expression is primarily restricted to the root tissues of Arabidopsis thaliana. This localization pattern has been demonstrated through β-glucuronidase (GUS) reporter gene fusions to the promoter region of MRS2-7. Unlike other MRS2 family members that show expression in multiple plant tissues, MRS2-7 expression is entirely restricted to the root at the seedling stage . This root-specific expression pattern correlates with its functional role in magnesium uptake from the soil and distribution within the plant. The expression of MRS2-7 does not appear to be regulated by environmental magnesium concentrations, as RT-PCR analyses using Arabidopsis plantlets raised on different magnesium concentrations (50, 500, or 1500 μM Mg2+) showed no evidence for magnesium-dependent regulation .
How is MRS2-7 localized within plant cells?
Green fluorescent protein (GFP) reporter gene fusions indicate that MRS2-7 is located in the endomembrane system within plant cells . This subcellular localization differs from some other members of the MRS2 family, which may be targeted to different cellular compartments including plasma membrane, mitochondria, or chloroplasts. Bioinformatic predictions also suggest that MRS2-7 may be localized to the cytoskeleton , although experimental evidence using GFP fusions supports the endomembrane system localization. The specific localization of MRS2-7 is important for its function in magnesium transport and homeostasis within different cellular compartments.
What experimental approaches have been used to characterize MRS2-7 function?
Several complementary experimental approaches have been used to characterize MRS2-7 function:
These complementary approaches have provided a comprehensive understanding of MRS2-7 function, localization, and its role in magnesium homeostasis.
How do MRS2-7 knockout mutants respond to different magnesium concentrations?
MRS2-7 knockout mutants exhibit a strong, magnesium-dependent phenotype that varies with external magnesium concentrations:
This magnesium-dependent phenotype is specific to mrs2-7 knockouts and is not observed in single-gene knockouts of other MRS2 family members such as MRS2-1, MRS2-5, and MRS2-10, or even in double knockout lines (mrs2-1 mrs2-5 and mrs2-5 mrs2-10) . This indicates a specialized, non-redundant role for MRS2-7 in magnesium homeostasis, particularly under limiting magnesium conditions.
Importantly, the growth retardation phenotype observed in mrs2-7 knockouts under low magnesium conditions can be complemented and even overcompensated by expressing MRS2-7 from the CaMV 35S promoter, leading to increased biomass accumulation compared to wild-type Arabidopsis .
Can MRS2-7 interact with other members of the MRS2/MGT family to form hetero-oligomers?
Yes, protein-protein interaction studies using the yeast mating-based split-ubiquitin system (mbSUS) have demonstrated that MRS2-7 can interact not only with itself but also with other members of the MRS2/MGT family to varying degrees . These interactions could potentially lead to the formation of hetero-oligomers, similar to the pentameric assemblies observed for bacterial CorA magnesium channels.
Key findings regarding MRS2-7 protein interactions include:
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MRS2-7 demonstrates homologous interactions with itself and heterologous interactions with other MRS2 proteins.
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Six amino acids may be deleted from the carboxy-terminus and 27 (but not 41) from the amino-terminus of MRS2-7 without impairing these protein-protein interactions .
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Despite significant sequence diversification among plant MRS2 proteins, they have retained the ancient CorA/MRS2 core structure and the capacity for protein-protein interactions.
The ability to form hetero-oligomers suggests that plant magnesium homeostasis may be influenced by channel formation where different plant MRS2 proteins meet in the same membrane, either naturally or in transgenic approaches . This could provide an additional layer of regulation for magnesium transport and homeostasis.
How does the efficiency of MRS2-7 in magnesium transport compare to other MRS2 family members?
Experimental data using the mag-fura-2 fluorescence assay has revealed variations in magnesium transport efficiency among different MRS2 family members:
MRS2-7 demonstrated high magnesium uptake efficiency comparable to MRS2-1 and MRS2-10 in direct Mg2+ uptake measurements using mag-fura-2 in isolated yeast mitochondria . This suggests that these three transporters are particularly effective at magnesium transport.
Interestingly, MRS2-3 showed good complementation in growth assays but relatively low magnesium uptake in the mag-fura-2 assay. This discrepancy suggests that MRS2-3 may act as a comparatively slow transporter for Mg2+, allowing for ion homeostasis over longer periods (hours) but not showing measurable transport over shorter time intervals (minutes) .
These differences in transport efficiency may reflect the specialized roles of different MRS2 family members in various tissues and cellular compartments.
What are the structural differences between human MRS2 and plant MRS2-7 that might affect function?
Human MRS2 and plant MRS2-7 share common structural features as members of the CorA-MRS2-ALR superfamily, but also exhibit important differences that may affect their function:
The human MRS2 structure determined by cryo-EM at 2.8 Å resolution in the presence of Mg2+ has provided detailed insights into its mechanism . Similar high-resolution structural studies of plant MRS2-7 would be valuable for understanding its specific mechanism of action and how it differs from the human counterpart.
These structural differences likely contribute to the specialized functions of MRS2 proteins in different organisms and cellular contexts.
How can researchers manipulate MRS2-7 expression to study its role in magnesium homeostasis?
Researchers can employ several strategies to manipulate MRS2-7 expression for studying its role in magnesium homeostasis:
These approaches have already yielded valuable insights into MRS2-7 function. For example, mrs2-7 knockout lines show severe growth retardation under limiting magnesium conditions (50 μM Mg2+), while ectopic overexpression from the CaMV 35S promoter not only complements this phenotype but leads to increased biomass accumulation compared to wild-type plants .
When designing experiments to manipulate MRS2-7, researchers should consider variables such as magnesium concentration in growth media, potential interactions with calcium and other divalent cations, and the possibility of compensatory mechanisms involving other magnesium transporters.
