Cloning and functional expression in Saccharomyces cereviae of a K+ transporter, AlHAK, from the graminaceous halophyte, Aeluropus littoralis.

High-affinity K(+) transporters play an important role in K(+) absorption of plants. We isolated a HAK gene from Aeluropus littoralis, a graminaceous halophyte. The amino acid sequence of AlHAK showed high homology with HAK transporters obtained from Oryza sativa (82%) and Hordeum vulgare (82%). When expressed in Saccharomyces cereviae WDelta3, AlHAK performed high-affinity K(+) uptake with a K(m) value of 8 muM, and the growth of transformants was dramatically inhibited by 150 mM Rb(+) and 150 mM Cs(+) but less affected by 300 mM Na(+). AlHAK may thus improve the capacity of plants to maintain a high cytosolic K(+)/Na(+) ratio at high salinity.