A PUTATIVE AMINO-ACID TRANSPORTER IS SPECIFICALLY EXPRESSED IN HAUSTORIA OF THE RUST FUNGUS UROMYCES-FABAE

A cDNA library constructed from haustoria of the rust fungus Uromyces fabae was screened for clones that are differentially expressed in hau storia, One family of cDNAs (in planta-induced gene 2 [PIG2]) was isol ated and found to encode a protein with high homologies to fungal amin o acid transporters, A cDNA clone containing the complete coding regio n of PIG2 and the corresponding genomic clone were isolated and sequen ced, revealing the presence of 17 introns in the PIG2 gene, Expression of PIG2 mRNA appeared to be restricted to haustoria, With antibodies raised against synthetic peptides, the PIG2-encoded protein was found in membrane fractions of isolated haustoria but not of germinated rust spores. With immunofluorescence microscopy, the putative amino acid t ransporter was localized to plasma membranes of the haustorial bodies, but not detected in the haustorial neck, haustorial mother cells, or intercellular fungal hyphae growing within infected leaf tissue, These data present for the first time molecular evidence that the rust haus torium plap a special role in the uptake of nutrients from an infected host cell.