title: Crosstalk between the unfolded protein response and pathways that regulate pathogenic development in Ustilago maydis.
abstract: The unfolded protein response (UPR) is a conserved eukaryotic signaling pathway regulating endoplasmic reticulum (ER) homeostasis during ER stress, which results, for example, from an increased demand for protein secretion. Here, we characterize the homologs of the central UPR regulatory proteins Hac1 (for Homologous to ATF/CREB1) and Inositol Requiring Enzyme1 in the plant pathogenic fungus Ustilago maydis and demonstrate that the UPR is tightly interlinked with the b mating-type-dependent signaling pathway that regulates pathogenic development. Exact timing of UPR is required for virulence, since premature activation interferes with the b-dependent switch from budding to filamentous growth. In addition, we found crosstalk between UPR and the b target Clampless1 (Clp1), which is essential for cell cycle release and proliferation in planta. The unusual C-terminal extension of the U. maydis Hac1 homolog, Cib1 (for Clp1 interacting bZIP1), mediates direct interaction with Clp1. The interaction between Clp1 and Cib1 promotes stabilization of Clp1, resulting in enhanced ER stress tolerance that prevents deleterious UPR hyperactivation. Thus, the interaction between Cib1 and Clp1 constitutes a checkpoint to time developmental progression and increased secretion of effector proteins at the onset of biotrophic development. Crosstalk between UPR and the b mating-type regulated developmental program adapts ER homeostasis to the changing demands during biotrophy.
authors.affiliation: Georg-August-University Göttingen, Institute for Microbiology and Genetics, Department of Molecular Microbiology and Genetics, 37077 Goettingen, Germany.
authors.forename: Kai
authors.initials: K
authors.lastname: Heimel
authors.forename: Johannes
authors.initials: J
authors.lastname: Freitag
authors.forename: Martin
authors.initials: M
authors.lastname: Hampel
authors.forename: Julia
authors.initials: J
authors.lastname: Ast
authors.forename: Michael
authors.initials: M
authors.lastname: Bölker
authors.forename: Jörg
authors.initials: J
authors.lastname: Kämper
mesh_terms: D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D059865:Endoplasmic Reticulum Stress; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D049770:Genes, Mating Type, Fungal; D008969:Molecular Sequence Data; D055550:Protein Stability; D015398:Signal Transduction; D056811:Unfolded Protein Response; D014588:Ustilago / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D003313:Zea mays / Q000382:microbiology
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D005656:Fungal Proteins