A Putative Amino Acid Transporter Is Specifically Expressed in Haustoria of the Rust Fungus Uromyces fabae

Abstract

A cDNA library constructed from haustoria of the rust fungus Uromyces fabae was screened for clones that are differentially expressed in haustoria. One family of cDNAs (in planta-induced gene 2 [PIG2]) was isolated and found to encode a protein with high homologies to fungal amino acid transporters. A cDNA clone containing the complete coding region of PIG2 and the corresponding genomic clone were isolated and sequenced, 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 transporter 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 haustorium plays a special role in the uptake of nutrients from an infected host cell.

The Powdery Mildew Disease of Arabidopsis: A Paradigm for the Interaction between Plants and Biotrophic Fungi

“…Successful penetration results in host plasma membrane invagination to accommodate the primary feeding structure of the fungus, the haustorium ( Figure 5, reviewed in O´Connell and . In biotrophic pathogens haustoria are believed to be responsible for the uptake of sugars and amino acids from the plant to the fungal mycelium (Hahn et al, 1997;Voegele et al, 2001) and are thought to actively deliver proteins (effectors) to suppress plant immune responses as is the case for rust fungi (Dodds et Conidiophore formation 4 dpi b 5 dpi 5 to 6 dpi 6 dpi c a Information was obtained from personal communications with D. Meyer as well as from the following publications: Adam and Somerville, 1996;Plotnikova et al, 1998;Adam et al, 1999, Vogel andSomerville, 2002. b hpi, hours post-inoculation; dpi, days post-inoculation; N/A: not available. c phenotype observed on tomato (Whipps et al, 1998;Jones et al, 2001) al.…”

Knocking on the heaven’s wall: pathogenesis of and resistance to biotrophic fungi at the cell wall

“…The presumed role of the haustorium in nutrient absorption has been supported experimentally by the identification and functional characterisation of proton-symportdriven transporters for hexose or amino acids that are resident in the haustorial membrane of the rust fungus U. vignae [53][54][55]. In contrast, the origin and function(s) of the extra-haustorial membrane of pathogenic biotrophs is still poorly understood.…”

Signal and nutrient exchange at biotrophic plant–fungus interfaces

“…Consistent with this view is the increased H + -ATPase activity in rust haustoria compared to that in spores and germlings, and the expression patterns of genes encoding two amino-acid transporters (AAT1 and AAT2) and a hexose transporter (HXT1) in haustoria of the broad bean rust fungus, Uromyces fabae. Although AAT1 is expressed in haustoria and intercellular hyphae, the transcripts and the proteins encoded by AAT2 and HXT1 have been detected only in haustoria [46,47]. Heterologous expression in transgenic yeast and Xenopus oocytes demonstrated that HXTP1p is a proton co-transporter specific for glucose and fructose [48].…”