title: A seven-WD40 protein related to human RACK1 regulates mating and virulence in Ustilago maydis.
abstract: In mammalian cells RACK1 serves as a scaffold protein that has a role in integrating inputs from different signalling pathways and affects translation through association with ribosomes. Ustilago maydis contains a seven-WD40 repeat motif protein designated Rak1, which shows 68% identity to RACK1 and 51% identity to Asc1p of Saccharomyces cerevisiae. An asc1 mutant could be complemented by introduction of U. maydis rak1. The deletion of rak1 affected cell growth, cell wall integrity and specifically attenuated cell fusion. This latter defect was caused by reduced expression of prf1 encoding the regulator for pheromone (mfa) and pheromone-receptor genes. Rak1 interacts with a variety of ribosomal proteins and microarray analysis revealed that the deletion of rak1 led to severely reduced expression of rop1, a transcriptional activator of prf1. The constitutive expression of rop1 could rescue the defect of mfa1 expression as well as conjugation tube formation in response to pheromone induction in the rak1 mutant. Moreover, a solopathogenic rak1 mutant failed to respond to plant-derived stimuli, resulting in attenuated filamentation and pathogenicity. This could be partially rescued by constitutive expression of the b heterodimer. These data suggest that rak1 is a regulator of rop1 expression with additional roles after cell fusion.
authors.affiliation: Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Strasse 10, D-35043 Marburg, Germany.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.forename: Patrick
authors.initials: P
authors.lastname: Berndt
authors.forename: Xiaojuan
authors.initials: X
authors.lastname: Xia
authors.forename: Jörg
authors.initials: J
authors.lastname: Kahnt
authors.forename: Regine
authors.initials: R
authors.lastname: Kahmann
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015966:Gene Expression Regulation, Fungal; D005816:Genetic Complementation Test; D000072235:Mating Factor; D008954:Models, Biological; D009363:Neoplasm Proteins / Q000235:genetics; D010455:Peptides / Q000378:metabolism*; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014588:Ustilago / Q000235:genetics / Q000502:physiology*; D014774:Virulence; D037521:Virulence Factors / Q000378:metabolism*
chemical_list: C111825:ASC1 protein, S cerevisiae; D048868:Adaptor Proteins, Signal Transducing; D005656:Fungal Proteins; D009363:Neoplasm Proteins; D010455:Peptides; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D029701:Saccharomyces cerevisiae Proteins; D037521:Virulence Factors; D000072235:Mating Factor; D019204:GTP-Binding Proteins