SEED AND VASCULAR EXPRESSION OF A HIGH-AFFINITY TRANSPORTER FOR CATIONIC AMINO-ACIDS IN ARABIDOPSIS

In most plants amino acids represent the major transport form for orga nic nitrogen. A sensitive selection system in yeast mutants has allowe d identification of a previously unidentified amino acid transporter i n Arabidopsis. AAT1 encodes a hydrophobic membrane protein with 14 mem brane-spanning regions and shares homologies with the ecotropic murine leukemia virus receptor, a bifunctional protein serving also as a cat ionic amino acid transporter in mammals, When expressed in yeast, AAT1 mediates high-affinity transport of basic amino acids, but to a lower extent also recognizes acidic and neutral amino acids, AAT1-mediated histidine transport is sensitive to protonophores and occurs against a concentration gradient, indicating that AAT1 may function as a proton symporter, AAT1 is specifically expressed in major veins of leaves an d roots and in various floral tissues-i.e., peduncle and developing se eds.