title: The fungal UmSrt1 and maize ZmSUT1 sucrose transporters battle for plant sugar resources.
abstract: The biotrophic fungus Ustilago maydis causes corn smut disease, inducing tumor formation in its host Zea mays. Upon infection, the fungal hyphae invaginate the plasma membrane of infected maize cells, establishing an interface where pathogen and host are separated only by their plasma membranes. At this interface the fungal and maize sucrose transporters, UmSrt1 and ZmSUT1, compete for extracellular sucrose in the corn smut/maize pathosystem. Here we biophysically characterized ZmSUT1 and UmSrt1 in Xenopus oocytes with respect to their voltage-, pH- and substrate-dependence and determined affinities toward protons and sucrose. In contrast to ZmSUT1, UmSrt1 has a high affinity for sucrose and is relatively pH- and voltage-independent. Using these quantitative parameters, we developed a mathematical model to simulate the competition for extracellular sucrose at the contact zone between the fungus and the host plant. This approach revealed that UmSrt1 exploits the apoplastic sucrose resource, which forces the plant transporter into a sucrose export mode providing the fungus with sugar from the phloem. Importantly, the high sucrose concentration in the phloem appeared disadvantageous for the ZmSUT1, preventing sucrose recovery from the apoplastic space in the fungus/plant interface.
authors.affiliation: Institute for Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, Biocenter, University of Würzburg, 97082 Würzburg, Germany.
authors.forename: Anke
authors.initials: A
authors.lastname: Wittek
authors.affiliation: Centro de Bioinformática y Simulación Molecular, Facultad de Ingeniería, Universidad de Talca, Talca, Chile.
authors.forename: Ingo
authors.initials: I
authors.lastname: Dreyer
authors.affiliation: College of Science, King Saud University, Riyadh 11451, Saudi Arabia.
authors.forename: Khaled A S
authors.initials: KAS
authors.lastname: Al-Rasheid
authors.affiliation: Molecular Plant Physiology, University Erlangen-Nürnberg, 91058 Erlangen, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Sauer
authors.affiliation: Institute for Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, Biocenter, University of Würzburg, 97082 Würzburg, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Hedrich
authors.affiliation: Institute for Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, Biocenter, University of Würzburg, 97082 Würzburg, Germany.
authors.forename: Dietmar
authors.initials: D
authors.lastname: Geiger
mesh_terms: D000818:Animals; D050260:Carbohydrate Metabolism; D054884:Host-Pathogen Interactions; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008954:Models, Biological; D010940:Plant Proteins / Q000378:metabolism*; D013395:Sucrose / Q000378:metabolism; D014588:Ustilago / Q000378:metabolism*; D014981:Xenopus; D003313:Zea mays / Q000378:metabolism / Q000382:microbiology*
chemical_list: D026901:Membrane Transport Proteins; D010940:Plant Proteins; C078729:sucrose transport protein, plant; D013395:Sucrose