The Rice monovalent cation transporter OsHKT2;4: Revisited ionic selectivity

Sassi Ali, Mieulet Delphine, Khan Imran, Moreau Bertrand, Gaillard Isabelle, Sentenac Hervé, Very Anne-Aliénor. 2012. The Rice monovalent cation transporter OsHKT2;4: Revisited ionic selectivity. Plant Physiology, 160 (1) : 498-510.

https://doi.org/10.1104/pp.112.194936

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Quartile : Outlier, Sujet : PLANT SCIENCES

Résumé : The family of plant membrane transporters named HKT (for high-affinity K+ transporters) can be subdivided into subfamilies 1 and 2, which, respectively, comprise Na+-selective transporters and transporters able to function as Na+-K+ symporters, at least when expressed in yeast (Saccharomyces cerevisiae) or Xenopus oocytes. Surprisingly, a subfamily 2 member from rice (Oryza sativa), OsHKT2;4, has been proposed to form cation/K+ channels or transporters permeable to Ca2+ when expressed in Xenopus oocytes. Here, OsHKT2;4 functional properties were reassessed in Xenopus oocytes. A Ca2+ permeability through OsHKT2;4 was not detected, even at very low external K+ concentration, as shown by highly negative OsHKT2;4 zero-current potential in high Ca2+ conditions and lack of sensitivity of OsHKT2;4 zero-current potential and conductance to external Ca2+. The Ca2+ permeability previously attributed to OsHKT2;4 probably resulted from activation of an endogenous oocyte conductance. OsHKT2;4 displayed a high permeability to K+ compared with that to Na+ (permeability sequence: K+ . Rb+ _ Cs+ . Na+ _ Li+ _ NH4 +). Examination of OsHKT2;4 current sensitivity to external pH suggested that H+ is not significantly permeant through OsHKT2;4 in most physiological ionic conditions. Further analyses in media containing both Na+ and K+ indicated that OsHKT2;4 functions as K+-selective transporter at low external Na+, but transports also Na+ at high (.10 mM) Na+ concentrations. These data identify OsHKT2;4 as a new functional type in the K+ and Na+-permeable HKT transporter subfamily. Furthermore, the high permeability to K+ in OsHKT2;4 supports the hypothesis that this system is dedicated to K+ transport in the plant.

Mots-clés Agrovoc : Oryza sativa, cytologie, propriété physicochimique, membrane cellulaire, potassium, sodium, calcium, Xenopus laevis, capacité d'échange ionique

Classification Agris : F61 - Physiologie végétale - Nutrition
L50 - Physiologie et biochimie animales
F60 - Physiologie et biochimie végétale

Champ stratégique Cirad : Axe 1 (2005-2013) - Intensification écologique

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