The rice monovalent cation transporter OsHKT2;4: revisited ionic selectivity
Ali Sassi1, Delphine Mieulet, Imran Khan
1Biochimie et Physiologie Moléculaire des Plantes, Unité Mixte de Recherche, 5004 Centre National de la Recherche Scientifique/386 Institut National de la Recherche Agronomique/SupAgro-M/Université Montpellier 2, Campus SupAgro-M, Montpellier cedex 2, France.
Plant Physiology
|July 10, 2012
Summary
OsHKT2;4, a rice transporter, does not transport Ca2+ but selectively transports K+ over Na+ at low Na+ concentrations. It functions as a K+ and Na+ permeable transporter, supporting its role in plant K+ uptake.
Area of Science:
- Plant biology
- Molecular biology
- Biochemistry
Background:
- High-affinity K(+) transporters (HKT) are crucial plant membrane transporters.
- HKT transporters are classified into subfamilies 1 (Na+-selective) and 2 (Na+-K+ symporters).
- OsHKT2;4 from rice was previously suggested to transport Ca2+.
Purpose of the Study:
- To reassess the functional properties of rice OsHKT2;4.
- To determine if OsHKT2;4 exhibits Ca2+ permeability.
- To characterize the ion selectivity and transport mechanism of OsHKT2;4.
Main Methods:
- Functional expression of OsHKT2;4 in Xenopus oocytes.
- Electrophysiological recordings to measure ion permeability and transport.
- Assessment of OsHKT2;4 current and potential sensitivity to external ion concentrations (K+, Na+, Ca2+) and pH.
Main Results:
- OsHKT2;4 did not show Ca2+ permeability; previously attributed Ca2+ permeability was likely due to endogenous oocyte conductance.
- OsHKT2;4 exhibited high permeability to K+ (K+ > Rb+ ≈ Cs+ > Na+ ≈ Li+ ≈ NH4+).
- OsHKT2;4 functions as a K+-selective transporter at low external Na+ but transports Na+ at high Na+ concentrations (>10 mM).
Conclusions:
- OsHKT2;4 is a novel functional type within the K+ and Na+-permeable HKT transporter subfamily.
- The high K+ permeability of OsHKT2;4 supports its role in plant K+ transport.
- OsHKT2;4's transport activity is dependent on external Na+ concentration, exhibiting selectivity for K+ under low Na+ conditions.
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