title: Rescue of Aspergillus nidulans severely debilitating null mutations in ESCRT-0, I, II and III genes by inactivation of a salt-tolerance pathway allows examination of ESCRT gene roles in pH signalling.
abstract: The Aspergillus pal pathway hijacks ESCRT proteins into ambient pH signalling complexes. We show that components of ESCRT-0, ESCRT-I, ESCRT-II and ESCRT-III are nearly essential for growth, precluding assessment of null mutants for pH signalling or trafficking. This severely debilitating effect is rescued by loss-of-function mutations in two cation tolerance genes, one of which, sltA, encodes a transcription factor whose inactivation promotes hypervacuolation. Exploiting a conditional expression sltA allele, we demonstrate that deletion of vps27 (ESCRT-0), vps23 (ESCRT-I), vps36 (ESCRT-II), or vps20 or vps32 (both ESCRT-III) leads to numerous small vacuoles, a phenotype also suppressed by SltA downregulation. This situation contrasts with normal vacuoles and vacuole-associated class E compartments seen in Saccharomyces cerevisiae ESCRT null mutants. Exploiting the suppressor phenotype of sltA(-) mutations, we establish that Vps23, Vps36, Vps20 and Vps32 are essential for pH signalling. Phosphatidylinositol 3-phosphate-recognising protein Vps27 (ESCRT-0) is not, consistent with normal pH signalling in rabB null mutants unable to recruit Vps34 kinase to early endosomes. In contrast to the lack of pH signalling in the absence of Vps20 or Vps32, detectable signalling occurs in the absence of ESCRT-III subunit Vps24. Our data support a model in which certain ESCRT proteins are recruited to the plasma membrane to mediate pH signalling.
authors.affiliation: Section of Microbiology, Imperial College London, Flowers Building, Armstrong Road, London SW7 2AZ,  UK.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Calcagno-Pizarelli
authors.forename: América
authors.initials: A
authors.lastname: Hervás-Aguilar
authors.forename: Antonio
authors.initials: A
authors.lastname: Galindo
authors.forename: Juan F
authors.initials: JF
authors.lastname: Abenza
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Peñalva
authors.forename: Herbert N
authors.initials: HN
authors.lastname: Arst
mesh_terms: D000483:Alleles; D001233:Aspergillus nidulans / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics* / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D050939:Gene Fusion; D005800:Genes, Fungal; D006863:Hydrogen-Ion Concentration; D010641:Phenotype; D021382:Protein Sorting Signals; D021381:Protein Transport; D055049:Salt Tolerance; D015398:Signal Transduction; D013489:Suppression, Genetic; D015533:Transcriptional Activation; D014617:Vacuoles / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000737:chemistry
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D005656:Fungal Proteins; D021382:Protein Sorting Signals; D033921:Vesicular Transport Proteins