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A Simple Protocol for Mapping the Plant Root System Architecture Traits
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Cellular pH homeostasis shapes root system architecture by modulating auxin-mediated developmental responses
Dimitris Templalexis1, Dikran Tsitsekian1, Gerasimos Daras1
1Department of Biotechnology, Agricultural University of Athens, Iera Odos 75, Athens 118 55, Greece.
Plant Physiology
|August 12, 2025
Summary
The TINY ROOT HAIR 1 (TRH1)/POTASSIUM (K+) UPTAKE 4 (KUP4) transporter maintains root cell elongation by balancing proton gradients. This transporter is crucial for root development under acidic conditions, preventing rhizotoxicity and enabling auxin transport.
Area of Science:
- Plant Biology
- Molecular Physiology
- Cell Biology
Background:
- Cell expansion requires turgor pressure and cell wall acidification.
- Auxin signaling typically promotes cell elongation via apoplast acidification, but inhibits it in roots through an unknown alkalinizing pathway.
- The TRH1/KUP4 transporter regulates auxin transport, influencing root gravitropism and root hair development.
Purpose of the Study:
- To investigate the role of TRH1/KUP4 in root development under acidic conditions.
- To elucidate the mechanism by which auxin transport and root cell elongation are modulated by pH.
- To understand the antagonistic pathway involved in root apoplast alkalinization.
Main Methods:
- Arabidopsis thaliana seedling growth assays under acidic conditions.
- Analysis of root hair length and gravitropic responses in wild-type and trh1/kup4 mutants.
- Application of exogenous auxin and pharmacological treatments.
- Advanced compartmental pH imaging to assess intracellular and apoplastic pH.
Main Results:
- Acidic conditions impair root hair growth and gravitropism in wild-type and trh1/kup4 seedlings, with exacerbated effects in mutants.
- Exogenous auxin partially rescues developmental defects in wild-type roots under acidic conditions.
- trh1/kup4 mutants exhibit cytoplasmic and vacuolar acidification, leading to AHA2 activation, apoplast acidification, and rhizotoxicity, inhibiting root elongation.
Conclusions:
- TRH1/KUP4 is essential for maintaining proton gradients, neutralizing cytoplasm, and alkalizing the apoplast in root cells.
- TRH1/KUP4 facilitates pH-driven auxin transport and modulates cell surface pH, crucial for root cell elongation and architecture.
- Acidity impairs active auxin transport by disrupting proton gradients, highlighting TRH1/KUP4's role in root adaptation to environmental pH.
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