title: Genetic bypass of Aspergillus nidulans crzA function in calcium homeostasis.
abstract: After dephosphorylation by the phosphatase calcineurin, the fungal transcription factor CrzA enters the nucleus and activates the transcription of genes responsible for calcium homeostasis and many other calcium-regulated activities. A lack of CrzA confers calcium-sensitivity to the filamentous fungus Aspergillus nidulans. To further understand calcium signaling in filamentous fungi and to identify genes that interact genetically with CrzA, we selected for mutations that were able to suppress crzAΔ calcium intolerance and identified three genes. Through genetic mapping, gene sequencing, and mutant rescue, we were able to identify these as cnaB (encoding the calcineurin regulatory subunit), folA (encoding an enzyme involved in folic acid biosynthesis, dihydroneopterin aldolase), and scrC (suppression of crzA(-), encoding a hypothetical protein). By using a calcium indicator, Fluo-3, we were able to determine that the wild-type and the suppressor strains were either able to regulate intracellular calcium levels or were able to take up and or store calcium correctly. The increased expression of calcium transporters, pmcA and/or pmcB, in suppressor mutants possibly enabled tolerance to high levels of calcium. Our results suggest that a cnaB suppressor mutation confers calcium tolerance to crzAΔ strains through restoration of calcium homeostasis. These results stress that in A. nidulans there are calcineurin-dependent and CrzA-independent pathways. In addition, it is possible that CrzA is able to contribute to the modulation of folic acid biosynthesis.
authors.affiliation: Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Brazil.
authors.forename: Ricardo S
authors.initials: RS
authors.lastname: Almeida
authors.forename: Omar
authors.initials: O
authors.lastname: Loss
authors.forename: Ana Cristina
authors.initials: AC
authors.lastname: Colabardini
authors.forename: Neil Andrew
authors.initials: NA
authors.lastname: Brown
authors.forename: Elaine
authors.initials: E
authors.lastname: Bignell
authors.forename: Marcela
authors.initials: M
authors.lastname: Savoldi
authors.forename: Sergio
authors.initials: S
authors.lastname: Pantano
authors.forename: Maria Helena S
authors.initials: MH
authors.lastname: Goldman
authors.forename: Herbert N
authors.initials: HN
authors.lastname: Arst
authors.forename: Gustavo H
authors.initials: GH
authors.lastname: Goldman
mesh_terms: D001232:Aspergillus fumigatus / Q000235:genetics / Q000378:metabolism; D001233:Aspergillus nidulans / Q000235:genetics* / Q000378:metabolism; D019703:Calcineurin / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000235:genetics; D002874:Chromosome Mapping; D005656:Fungal Proteins / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal; D006706:Homeostasis; D013489:Suppression, Genetic
chemical_list: C530975:CrzA protein, Aspergillus fumigatus; D005656:Fungal Proteins; D019703:Calcineurin; D002118:Calcium
keywords: Aspergillus nidulan; CrzA; calcineurin; extragenic suppression; folate biosynthesis