The Uromyces fabae UfAAT3 gene encodes a general amino acid permease that prefers uptake of in planta scarce amino acids

Abstract

SUMMARY The obligately biotrophic rust fungi are dependent on nutrient supply from their host plants. A cDNA library of infection structures of the rust fungus Uromyces fabae was used to identify a gene (UfAAT3) that encodes a protein with a high degree of sequence similarity to fungal amino acid permeases. The expression profile revealed by RT-PCR shows an up-regulation very early during rust development, with the highest level in haustoria and infected leaves. Heterologous expression of UfAAT3p in Xenopus oocytes revealed an amino acid permease energized by co-transport with protons and exhibiting a broad substrate specificity. Compared to the previously described U. fabae amino acid transporter (AAT1), which represented the highest transport activities for lysine and histidine, electrophysiological measurements with cRNA of UfAAT3-injected oocytes showed substrate preferences for leucine and the sulphur containing amino acids methionine and cysteine. The unique contribution of the amino acid permeases and their substrate affinities might be connected with the availability of amino acids in the leaf tissue. Thus, in order to compare the substrate profiles of AAT1p and UfAAT3p with the natural environment of U. fabae we analysed the amino acid concentration in the apoplastic space, in addition to that in extracts of Vicia faba leaves. The predominant free amino acids were asparagine, alanine, glutamine and glutamate. However, most amino acids were present at low concentrations (between 0.02 and 0.16 mm), including the preferred substrates of the U. fabae amino acid permeases AAT1p and UfAAT3p.

Microarray analysis of expressed sequence tags from haustoria of the rust fungus Uromyces fabae

“…Upregulation of a 4-aminobutyrate (GABA) aminotransferase has also been observed in the biotrophic fungus Cladosporium fulvum during infection (Solomon and Oliver, 2002). Low but signiWcant concentrations of GABA have been detected in the apoplast of rust-infected broad bean leaves (Struck et al, 2004). As it has been proposed for C. fulvum, GABA might be a signiWcant nitrogen source for biotrophic fungi in general.…”

“…It has previously been shown that in U. fabae, at least three amino acid permeases are expressed in the biotrophic mycelium. While PIG2p (AAT2p) has an unknown substrate speciWcity , AAT1p (PIG27p) is speciWc for lysine and histidine (Struck et al, 2002), and AAT3p is a broad speciWcity amino acid transporter (Struck et al, 2004). Based on the gene expression data for these transporters, amino acid uptake seems to occur both via haustoria and via intercellular hyphae.…”

The Amino Acid Permeases AAP3 and AAP6 Are Involved in Root-Knot Nematode Parasitism of Arabidopsis

“…Amino acid transporters are central to infection for several other obligate pathogens such as fungal, protozoan, and insect parasites. The rust fungus Uromyces fabae induces expression of a general amino acid permease, UtAAT3, in haustoria to acquire amino acids from the leaf apoplast (Struck et al 2004). The expression of the cationic amino acid transporter CAT2B from mouse is upregulated during Leishmania amazonensis infection, thereby providing the arginine necessary for proliferation of the parasite (Wanasen et al 2007).…”

Reduced Carbohydrate Availability Enhances the Susceptibility of Arabidopsis toward Colletotrichum higginsianum

“…During biotrophy, an interface between the fungal and the host plasma membrane is formed, through which solute exchange and effector delivery to the host takes place (for review, see Divon and Fluhr, 2007;Stergiopoulos and de Wit, 2009). Evidence obtained for the rust fungus Uromyces fabae suggests that host assimilates are mainly taken up in the form of hexoses generated from secreted fungal invertase and amino acids (Voegele et al, 2001;Struck et al, 2002Struck et al, , 2004. Recently, a high-affinity Suc transporter from the corn smut fungus Ustilago maydis was described that suggests a direct uptake of Suc in this pathosystem (Wahl et al, 2010).…”