THE HAK1 GENE OF BARLEY IS A MEMBER OF A LARGE GENE FAMILY AND ENCODES A HIGH-AFFINITY POTASSIUM TRANSPORTER

The high-affinity K+ uptake system of plants plays a crucial role in n utrition and has been the subject of extensive kinetic studies. Howeve r, major components of this system remain to be identified. We isolate d a cDNA from barley roots, HvHAK1, whose translated sequence shows ho mology to the Escherichia coli Kup and Schwanniomyces occidentalis HAK 1 K+ transporters. HVHAK1 conferred high-affinity K+ uptake to a K+-up take-deficient yeast mutant exhibiting the hallmark characteristics of the high-affinity K+ uptake described for barley roots. HVHAK1 also m ediated low-affinity Na+ uptake. Another cDNA (HvHAK2) encoding a poly peptide 42% identical to HvHAK1 was also isolated. Analysis of several genomes of Triticeae indicates that HVHAK1 belongs to a multigene fam ily. Translated sequences from bacterial DNAs and Arabidopsis, rice, a nd possibly human cDNAs show homology to the Kup-HAK1-HvHAK1 family of K+ transporters.