K+ Transport by the OsHKT2;4 Transporter from Rice with Atypical Na+ Transport Properties and Competition in Permeation of K+ over Mg2+ and Ca2+ Ions
Open Access
- 24 May 2011
- journal article
- Published by Oxford University Press (OUP) in Plant Physiology
- Vol. 156 (3), 1493-1507
- https://doi.org/10.1104/pp.110.168047
Abstract
Members of class II of the HKT transporters, which have thus far only been isolated from grasses, were found to mediate Na+-K+ cotransport and at high Na+ concentrations preferred Na+-selective transport, depending on the ionic conditions. But the physiological functions of this K+-transporting class II of HKT transporters remain unknown in plants, with the exception of the unique class II Na+ transporter OsHKT2;1. The genetically tractable rice (Oryza sativa; background Nipponbare) possesses two predicted K+-transporting class II HKT transporter genes, OsHKT2;3 and OsHKT2;4. In this study, we have characterized the ion selectivity of the class II rice HKT transporter OsHKT2;4 in yeast and Xenopus laevis oocytes. OsHKT2;4 rescued the growth defect of a K+ uptake-deficient yeast mutant. Green fluorescent protein-OsHKT2;4 is targeted to the plasma membrane in transgenic plant cells. OsHKT2;4-expressing oocytes exhibited strong K+ permeability. Interestingly, however, K+ influx in OsHKT2;4-expressing oocytes did not require stimulation by extracellular Na+, in contrast to other class II HKT transporters. Furthermore, OsHKT2;4-mediated currents exhibited permeabilities to both Mg2+ and Ca2+ in the absence of competing K+ ions. Comparative analyses of Ca2+ and Mg2+ permeabilities in several HKT transporters, including Arabidopsis thaliana HKT1;1 (AtHKT1;1), Triticum aestivum HKT2;1 (TaHKT2;1), OsHKT2;1, OsHKT2;2, and OsHKT2;4, revealed that only OsHKT2;4 and to a lesser degree TaHKT2;1 mediate Mg2+ transport. Interestingly, cation competition analyses demonstrate that the selectivity of both of these class II HKT transporters for K+ is dominant over divalent cations, suggesting that Mg2+ and Ca2+ transport via OsHKT2;4 may be small and would depend on competing K+ concentrations in plants.Keywords
This publication has 70 references indexed in Scilit:
- Crystal structure of a potassium ion transporter, TrkHNature, 2011
- High-Affinity K+ Transport in Arabidopsis: AtHAK5 and AKT1 Are Vital for Seedling Establishment and Postgermination Growth under Low-Potassium ConditionsPlant Physiology, 2010
- A rice high-affinity potassium transporter (HKT) conceals a calcium-permeable cation channelProceedings of the National Academy of Sciences, 2010
- Differential Sodium and Potassium Transport Selectivities of the Rice OsHKT2;1 and OsHKT2;2 Transporters in Plant CellsPlant Physiology, 2009
- HKT transporter-mediated salinity resistance mechanisms in Arabidopsis and monocot crop plantsTrends in Plant Science, 2009
- Shoot Na+ Exclusion and Increased Salinity Tolerance Engineered by Cell Type–Specific Alteration of Na+ Transport in ArabidopsisPlant Cell, 2009
- Diversity in Expression Patterns and Functional Properties in the Rice HKT Transporter FamilyPlant Physiology, 2009
- Rice OsHKT2;1 transporter mediates large Na+ influx component into K+-starved roots for growthThe EMBO Journal, 2007
- HKT1;5-Like Cation Transporters Linked to Na+ Exclusion Loci in Wheat, Nax2 and Kna1Plant Physiology, 2007
- A Sodium Transporter (HKT7) Is a Candidate forNax1, a Gene for Salt Tolerance in Durum WheatPlant Physiology, 2006