Characterization of a developmentally regulated amino acid transporter (AAT1p) of the rust fungus Uromyces fabae

In the rust fungus Uromyces fabae, invasion of the host plant and haustorium formation are accompanied by the activation of many genes (PIGs = in planta induced genes). In addition to the previously described AAT2 (PIG2), AAT1 (PIG27) was found to encode a protein with a high similarity to fungal amino acid permeases. AAT1 transcripts are present in germinated hyphae and throughout the mycelium later in the infection process, but occur at the highest levels in haustoria. Expression of AAT1 p in a histidine uptake-defective yeast mutant revealed energy-dependent transport of C-14-histidine, with a K-m value of 25.8 mum. In addition, complementation analysis revealed AAT1-dependent transport for lysine. Using Xenopus oocytes as expression system, AAT1p-dependent symport of protons with a broad spectrum of amino acids was observed, with the highest activities obtained with histidine and lysine. These results confirm that in rust fungi, the expression of amino acid transporters is developmentally regulated and occurs preferentially in the parasitic phase of development.