Cloning and expression of amino acid transporters from broad bean

This work describes the isolation of a full-length (VfAAP2) and three parti al amino acid transporter genes (VfAAPa, VfAAPb, VfAAPc) from broad bean (V icia faba L.). The function of VfAAP2 was tested by heterologous expression in a yeast mutant deficient in proline uptake. VfAAP2 mediates proton-depe ndent proline uptake with an apparent K-m of about 1 mM. Analysis of substr ate specificity by competition experiments showed that aromatic amino acids , neutral aliphatic acids and L-citrulline are the best competitors, wherea s basic amino acids do not compete with proline. Northern analysis indicate s that all VfAAPs exhibit different patterns of expression. VfAAP2 is most strongly expressed in the stem and at a lower level in sink leaves and pods . VfAAPa, VfAAPb and VfAAPc are most strongly expressed in the flowers, but their expression in the other organs varies.