NRT2.1 Antibody

What is NRT2.1 and why is it important in plant research?

NRT2.1 (Nitrate Transporter 2.1) is a high-affinity nitrate transporter primarily studied in Arabidopsis thaliana. It serves as a main component of the root nitrate high-affinity transport system and functions as a repressor of lateral root initiation independently of nitrate uptake . NRT2.1 is critically important in plant research because:

• It plays a central role in nitrogen acquisition, particularly under low nitrate conditions

• It connects nutrient sensing with developmental responses like lateral root formation

• It demonstrates complex regulatory mechanisms at transcriptional and post-translational levels

• It has been shown to interact with NAR2.1 to form a functional nitrate transport complex

• Understanding its function helps develop crops with improved nitrogen use efficiency

The protein is known by several synonyms including ACH1, ATNRT2.1, ATNRT2:1, LATERAL ROOT INITIATION 1 (LIN1), and others .

What are the key considerations when selecting an NRT2.1 antibody?

When selecting an NRT2.1 antibody for research applications, several important factors should be considered:

• Epitope specificity: The epitope location can be critical. For example, antibodies targeting the C-terminus (such as anti-NRT2.1 20, which targets an epitope 18 amino acids upstream of the C-terminus) may detect different forms of the protein than those targeting other regions .

• Cross-reactivity: Verify the predicted reactivity across species. Available antibodies may cross-react with NRT2.1 in Brassica species (B. juncea, B. napus, B. rapa) and some other plants like Ricinus communis or Solanum lycopersicum .

• Application compatibility: Ensure the antibody is validated for your intended application. Current commercial antibodies are primarily validated for Western blotting .

• Clonality: Polyclonal antibodies (like the rabbit polyclonal described in the search results) provide good sensitivity but may have batch-to-batch variation .

• Phospho-specific needs: For studies on post-translational regulation, consider whether you need phospho-specific antibodies that can detect specific phosphorylation sites like S501 .

How should NRT2.1 antibodies be stored and reconstituted?

Proper storage and reconstitution of NRT2.1 antibodies is essential for maintaining their activity and specificity:

• Storage temperature: Store lyophilized or reconstituted antibodies at -20°C .

• Reconstitution procedure: For lyophilized antibodies, add 50 μL of sterile water to reconstitute .

• Avoiding freeze-thaw cycles: Once reconstituted, make aliquots to avoid repeated freeze-thaw cycles that can degrade antibody quality .

• Preparation before use: Spin tubes briefly prior to opening them to avoid any losses that might occur from lyophilized material adhering to the cap or sides of the tubes .

• Working dilution: For Western blotting applications, a typical dilution is 1:5000 with standard ECL detection systems .

What is the most effective protein extraction method for detecting NRT2.1?

The detection of NRT2.1 requires careful consideration of protein extraction methods:

• Recommended fraction: Microsomal fraction is strongly recommended as it contains higher amounts of NRT2.1 protein compared to total protein extracts .

• Use of detergents: If using total protein extract, SDS should be applied from the beginning in the extraction buffer to solubilize membrane proteins effectively .

• Protease inhibition: A protease inhibitor cocktail is essential to prevent degradation of NRT2.1 during extraction .

• Expected molecular weight: NRT2.1 typically appears at approximately 45 kDa on Western blots, though the theoretical molecular weight is 57.7 kDa .

• Multimeric forms: Higher molecular weight bands at approximately 100 kDa and 130 kDa may be observed, likely representing multimeric forms of NRT2.1 .

For optimal results, researchers should prepare microsomal fractions from fresh plant tissues and maintain cold temperatures throughout the extraction process.

How can I detect phosphorylated forms of NRT2.1?

Detection of phosphorylated NRT2.1 requires specific approaches:

• Phospho-specific antibodies: Use antibodies specifically raised against phosphorylated epitopes, such as anti-S501P antibody for detecting phosphorylation at serine 501 .

• Protein abundance considerations: The amount of NRT2.1 after certain treatments (like nitrogen starvation) may be too low to detect the phosphorylated form, even with phospho-specific antibodies .

• Induction treatments: To optimize detection of phosphorylated forms, consider inducing plants with nitrate (e.g., 1 mM NO₃⁻) for specific time periods (1-4 hours) following nitrogen starvation .

• Quantitative analysis: ELISA using both phospho-specific and general anti-NRT2.1 antibodies can provide quantitative data on phosphorylation levels .

• Western blot considerations: Both monomeric (~45 kDa) and multimeric forms (~100-130 kDa) of phosphorylated NRT2.1 may be detected, with different patterns of phosphorylation in each form .

Research has shown that S501 phosphorylation status changes in response to nitrate treatments, with evidence suggesting that dephosphorylation at S501 correlates with increased NRT2.1 activity .

What controls should be included when working with NRT2.1 antibodies?

Proper experimental controls are crucial when working with NRT2.1 antibodies:

• Negative control: Include samples from nrt2.1 knockout mutants (like the nrt2.1-2 mutant) to confirm antibody specificity .

• Phosphorylation controls: When studying phosphorylation, transgenic plants expressing phosphomimetic (e.g., S501D) or phospho-null (e.g., S501A) variants of NRT2.1 can serve as important controls .

• Loading controls: Include membrane protein loading controls appropriate for microsomal fractions.

• Time course controls: When studying responses to nitrate treatments, include multiple time points (e.g., 1h and 4h after treatment) to capture dynamics of protein expression and modification .

• Cross-reactivity controls: If working with species other than Arabidopsis, validate antibody specificity in your species of interest before proceeding with experiments.

These controls help ensure reliable interpretation of results and identification of specific NRT2.1 bands versus non-specific binding.

How do post-translational modifications affect NRT2.1 function?

Post-translational modifications play a crucial role in regulating NRT2.1 function:

• Phosphorylation at S501: Research has demonstrated that phosphorylation at serine 501 can inactivate NRT2.1 function. This has been confirmed through transgenic plants expressing phosphomimetic substitutions (S501D), which showed dramatically reduced high-affinity nitrate uptake .

• C-terminal processing: Evidence suggests that NRT2.1 undergoes partial proteolysis at its C-terminus, which may regulate its activity. Studies using truncated forms of NRT2.1 (ΔC 494-530 and ΔC 514-530) identified an essential sequence for NRT2.1 activity located between residues 494-513 .

• Effect on protein-protein interactions: Post-translational modifications don't appear to prevent interaction with NAR2.1, as phosphomimetic NRT2.1 variants (S501D) still formed complexes with NAR2.1 similar to wild-type or phospho-null (S501A) variants .

• Impact on protein stability: Some modifications may affect NRT2.1 protein abundance. For instance, S501D plants showed lower levels of NRT2.1 protein compared to S501A and wild-type plants .

The research suggests a model where dephosphorylation of S501 in response to nitrate treatment activates NRT2.1, providing a rapid post-translational regulatory mechanism independent of transcriptional control .

Why might I observe multiple bands for NRT2.1 in Western blots?

The observation of multiple bands in NRT2.1 Western blots is common and has biological significance:

• Expected band sizes: The monomeric form of NRT2.1 typically appears at ~45 kDa, while higher molecular weight bands at ~100 kDa and ~130 kDa likely represent multimeric forms .

• Confirmation of specificity: All these bands should be absent in nrt2.1 knockout mutants, confirming they represent specific detection of NRT2.1 protein .

• Differential phosphorylation: The phosphorylation status may differ between monomeric and multimeric forms. Research has shown that after nitrate treatment, phosphorylated NRT2.1 decreased in the multimeric forms while increasing in the monomeric form, suggesting a redistribution of phosphorylated protein .

• Membrane protein characteristics: As a membrane protein, NRT2.1 may not completely dissociate during SDS-PAGE sample preparation, leading to the appearance of dimers or other oligomeric forms.

• C-terminal processing: Partial proteolysis of the C-terminus may generate truncated forms of NRT2.1 that appear as additional bands .

The pattern of these multiple bands may change depending on experimental conditions and treatments, providing valuable information about NRT2.1 regulation and dynamics.

How can I distinguish between transcriptional and post-translational regulation of NRT2.1?

Distinguishing between transcriptional and post-translational regulation of NRT2.1 requires complementary approaches:

• Transcript vs. protein abundance comparison:

  • Measure NRT2.1 mRNA levels via RT-qPCR

  • Simultaneously quantify protein levels via Western blotting

  • Discrepancies between mRNA and protein changes suggest post-translational regulation

• Phosphorylation status monitoring:

  • Use phospho-specific antibodies (like anti-S501P) alongside total NRT2.1 antibodies

  • Calculate the ratio of phosphorylated to total NRT2.1 protein

  • Changes in this ratio without corresponding mRNA changes indicate post-translational regulation

• Transgenic approaches:

  • Express NRT2.1 under constitutive promoters to eliminate transcriptional regulation

  • Compare plants expressing wild-type NRT2.1 versus phospho-variants (S501A or S501D)

  • Differences in nitrate uptake between these lines (with similar protein levels) would confirm post-translational regulation

• Activity assays:

  • Measure high-affinity nitrate uptake under conditions where NRT2.1 protein levels remain constant

  • Rapid changes in uptake without protein level changes suggest post-translational regulation

Research has shown that while NRT2.1 is subject to complex transcriptional regulation by nitrate, N metabolites, light, and sugars, post-translational regulation through phosphorylation provides an additional rapid control mechanism .

How should I interpret changes in NRT2.1 phosphorylation in response to nitrate treatments?

Interpreting changes in NRT2.1 phosphorylation requires careful analysis:

• Inverse correlation with activity: Research suggests that phosphorylation at S501 negatively regulates NRT2.1 activity. When plants are exposed to nitrate, the proportion of NRT2.1 phosphorylated at S501 decreases relative to total NRT2.1, correlating with increased transporter activity .

• Timing considerations:

  • After 4h of nitrate re-supply (following N starvation), total NRT2.1 protein increases

  • The level of S501-phosphorylated NRT2.1 may not change in absolute terms

  • This leads to a decrease in the phosphorylated fraction relative to total protein

• Distribution between monomeric and multimeric forms:

  • S501-phosphorylated NRT2.1 appears to redistribute from multimeric to monomeric forms after nitrate treatment

  • This redistribution may represent a mechanism for regulating activity through protein complex dynamics

• Quantitative assessment: When analyzing Western blots, consider:

  Time after NO₃⁻ supply	Total NRT2.1 (relative)	S501-P NRT2.1 (relative)	S501-P/Total ratio
  1h	1.0	1.0	High
  4h	↑ (~1.5-2.0)	~ unchanged	Lower

This pattern is consistent with a model where dephosphorylation at S501 during sustained nitrate exposure contributes to activation of NRT2.1-mediated nitrate uptake .

What explains the discrepancy between ELISA and Western blot results when analyzing NRT2.1 phosphorylation?

The research results reveal an interesting discrepancy between ELISA and Western blot analysis of NRT2.1 phosphorylation that requires careful interpretation:

This case highlights the importance of using multiple analytical techniques when studying complex post-translational modifications and protein complexes.

How can I correlate NRT2.1 protein levels and post-translational modifications with functional activity?

Correlating NRT2.1 protein dynamics with its functional activity requires integrating multiple experimental approaches:

• Nitrate uptake assays: Measure high-affinity nitrate uptake in intact roots using ¹⁵N-labeled nitrate or equivalent methods to quantify transport activity .

• Protein analysis:

  • Quantify total NRT2.1 protein levels via Western blot using anti-NRT2.1 antibodies

  • Determine S501 phosphorylation status using phospho-specific antibodies

  • Calculate the ratio of phosphorylated to total NRT2.1

• Genetic approaches: Compare wild-type plants with:

  • nrt2.1 knockout mutants (complete loss of function)

  • Phosphomimetic mutants (S501D) simulating constitutive phosphorylation

  • Phospho-null mutants (S501A) preventing phosphorylation at the S501 site

• Correlation analysis: Create data tables like the following to identify patterns:

  Genotype/Treatment	Nitrate Uptake (relative)	Total NRT2.1	S501-P NRT2.1	S501-P/Total Ratio
  WT (N-starved)	Low	Low	Variable	High
  WT (1h NO₃⁻)	Medium	Medium	Medium	Medium
  WT (4h NO₃⁻)	High	High	Medium	Low
  nrt2.1 mutant	Very low	None	None	N/A
  S501A	High	Medium-High	None	Zero
  S501D	Very low	Lower	N/A	N/A

Research demonstrates that despite having detectable NRT2.1 protein and normal interaction with NAR2.1, S501D plants show dramatically reduced nitrate uptake, supporting the model that S501 phosphorylation directly inhibits NRT2.1 transport activity .

How should I design experiments to investigate the role of S501 phosphorylation in NRT2.1 regulation?

Designing effective experiments to study S501 phosphorylation requires comprehensive planning:

• Complementation studies:

  • Generate transgenic plants expressing NRT2.1 variants in the nrt2.1 knockout background

  • Include wild-type NRT2.1, phosphomimetic (S501D), and phospho-null (S501A) variants

  • Use the native NRT2.1 promoter to maintain physiological expression patterns

  • Measure growth phenotypes, nitrate uptake, and protein levels to assess function

• Temporal dynamics:

  • Design time-course experiments following nitrate re-supply

  • Include early (1h) and later (4h) time points to capture dynamic changes

  • Simultaneously measure nitrate uptake, total NRT2.1, and phosphorylated NRT2.1

• Protein interaction studies:

  • Use techniques like BiFC (Bimolecular Fluorescence Complementation) to assess interaction with NAR2.1

  • Compare interaction efficiency between wild-type and phosphovariant forms of NRT2.1

  • Include quantification controls (like RFP fluorescence) for normalization

• Physiological relevance:

  • Include experiments under different nitrogen regimes that mimic natural conditions

  • Compare responses to sustained versus transient nitrate availability

  • Correlate molecular data with whole-plant phenotypes like growth and lateral root development

Research using this approach has successfully demonstrated that S501 phosphorylation serves as a molecular switch that can inactivate NRT2.1 function, providing a rapid post-translational regulatory mechanism .

What approaches can reveal the molecular mechanisms controlling NRT2.1 phosphorylation?

Uncovering the mechanisms controlling NRT2.1 phosphorylation requires multiple complementary approaches:

• Identification of responsible kinases and phosphatases:

  • Perform kinase/phosphatase inhibitor studies to determine enzyme classes involved

  • Conduct protein-protein interaction screens (Y2H, co-IP) to identify candidates

  • Test candidate enzymes through in vitro phosphorylation/dephosphorylation assays

  • Validate in planta through genetic approaches (mutants, overexpression)

• Signal transduction pathways:

  • Test the effects of various nitrogen sources and metabolites

  • Investigate cross-talk with other signaling pathways (sugar, hormone, stress)

  • Use pharmacological approaches to disrupt specific signaling components

  • Employ genetic approaches with signaling mutants

• Structural studies:

  • Generate structural models of NRT2.1 focusing on the C-terminal region (494-513)

  • Determine how S501 phosphorylation might affect protein conformation

  • Investigate whether phosphorylation influences interaction with other proteins beyond NAR2.1

• Advanced phosphoproteomic approaches:

  • Employ quantitative phosphoproteomics to identify all NRT2.1 phosphorylation sites

  • Determine which sites show coordinated regulation

  • Identify conditions that trigger phosphorylation/dephosphorylation events

Such approaches would extend the current understanding that S501 phosphorylation status is modulated by nitrate availability, suggesting the existence of nitrate-responsive signaling pathways that control the activity of relevant kinases or phosphatases .

How does NRT2.1 regulation compare with other nitrate transporters?

Understanding NRT2.1 regulation in the context of other nitrate transporters provides valuable comparative insights:

• Comparison with other NRT2 family members:

  • While NRT2.1 is the most abundant high-affinity nitrate transporter in Arabidopsis roots, other family members (NRT2.2-NRT2.7) have specialized functions and potentially different regulatory mechanisms

  • NRT2.1 regulation through phosphorylation may be unique or shared among family members

  • Sequence alignment of the region containing S501 across NRT2 family members could indicate conservation of this regulatory mechanism

• Comparison with NRT1/NPF family:

  • Unlike NRT2.1, some NRT1/NPF transporters (low-affinity family) are known to function as nitrate sensors/transceptors

  • NRT1.1/CHL1/NPF6.3 undergoes phosphorylation at T101, which switches its affinity from low to high

  • This represents a different phosphorylation-based regulatory mechanism than NRT2.1, where S501 phosphorylation appears to inactivate the transporter

• Functional coordination:

  Transporter	Affinity	Regulation by Phosphorylation	Function when Phosphorylated
  NRT2.1	High	S501	Inactive
  NRT1.1	Low/High	T101	Switches to high affinity
  Other NRT2s	High	Under investigation	Unknown
  Other NPFs	Low	Various sites	Diverse effects

Understanding these comparative aspects helps place NRT2.1 regulation in a broader context of nitrogen acquisition strategies in plants.

What is the significance of the NRT2.1/NAR2.1 complex for antibody-based detection?

The NRT2.1/NAR2.1 complex formation has important implications for antibody-based detection and experimental design:

• Complex formation requirement:

  • NRT2.1 requires association with NAR2.1 to form a functional nitrate transport system

  • This two-component system affects how NRT2.1 exists in native membranes

• Detection considerations:

  • Antibodies may have different accessibilities to epitopes depending on complex formation

  • The ~400 kDa complex observed in Blue Native PAGE contains both NRT2.1 and NAR2.1

  • Higher molecular weight bands in standard Western blots may represent partially denatured complexes

• Experimental validation:

  • Research has used both Western blotting and rBiFC (ratiometric Bimolecular Fluorescence Complementation) to confirm interaction between NRT2.1 variants and NAR2.1

  • The quantification of fluorescence signals showed similar interaction efficiency between NAR2.1 and either wild-type NRT2.1 or phosphovariant forms (S501A, S501D)

• Functional implications:

  • Despite normal complex formation with NAR2.1, phosphomimetic S501D NRT2.1 lacks transport activity

  • This indicates that S501 phosphorylation affects a step after complex formation, possibly by altering the transport mechanism itself

These findings are significant because they demonstrate that antibody detection of NRT2.1 must consider its existence in protein complexes, and that regulatory mechanisms can act on the assembled complex rather than preventing complex formation.

This understanding helps researchers properly interpret Western blot results and design experiments that account for the dimeric nature of the functional nitrate transport system.