title: Physical and genetic interaction between ammonium transporters and the signaling protein Rho1 in the plant pathogen Ustilago maydis.
abstract: Dimorphic transitions between yeast-like and filamentous forms occur in many fungi and are often associated with pathogenesis. One of the cues for such a dimorphic switch is the availability of nutrients. Under conditions of nitrogen limitation, fungal cells (such as those of Saccharomyces cerevisiae and Ustilago maydis) switch from budding to pseudohyphal or filamentous growth. Ammonium transporters (AMTs) are responsible for uptake and, in some cases, for sensing the availability of ammonium, a preferred nitrogen source. Homodimer and/or heterodimer formation may be required for regulating the activity of the AMTs. To investigate the potential interactions of Ump1 and Ump2, the AMTs of the maize pathogen U. maydis, we first used the split-ubiquitin system, followed by a modified split-YFP (yellow fluorescent protein) system, to validate the interactions in vivo. This analysis showed the formation of homo- and hetero-oligomers by Ump1 and Ump2. We also demonstrated the interaction of the high-affinity ammonium transporter, Ump2, with the Rho1 GTPase, a central protein in signaling, with roles in controlling polarized growth. This is the first demonstration in eukaryotes of the physical interaction in vivo of an ammonium transporter with the signaling protein Rho1. Moreover, the Ump proteins interact with Rho1 during the growth of cells in low ammonium concentrations, a condition required for the expression of the Umps. Based on these results and the genetic evidence for the interaction of Ump2 with both Rho1 and Rac1, another small GTPase, we propose a model for the role of these interactions in controlling filamentation, a fundamental aspect of development and pathogenesis in U. maydis.
authors.affiliation: Department of Biology, Program on Disease Evolution, University of Louisville, Louisville, Kentucky, USA.
authors.forename: Jinny A
authors.initials: JA
authors.lastname: Paul
authors.affiliation: Kidney Disease Program, University of Louisville, Louisville, Kentucky, USA.
authors.forename: Michelle T
authors.initials: MT
authors.lastname: Barati
authors.affiliation: Department of Biology, Program on Disease Evolution, University of Louisville, Louisville, Kentucky, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Cooper
authors.affiliation: Department of Biology, Program on Disease Evolution, University of Louisville, Louisville, Kentucky, USA michael.perlin@louisville.edu.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Perlin
mesh_terms: D000595:Amino Acid Sequence; D000242:Cyclic AMP; D005656:Fungal Proteins / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal / Q000235:genetics; D025301:Hyphae / Q000235:genetics / Q000254:growth & development; D017136:Ion Transport / Q000235:genetics*; D018832:Molecular Chaperones / Q000235:genetics; D009584:Nitrogen / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D015398:Signal Transduction; D014588:Ustilago / Q000235:genetics* / Q000254:growth & development; D003313:Zea mays / Q000382:microbiology
chemical_list: D005656:Fungal Proteins; D018832:Molecular Chaperones; C110856:proteasome maturation protein; D000242:Cyclic AMP; D009584:Nitrogen