title: Genomic and functional analyses unveil the response to hyphal wall stress in Candida albicans cells lacking β(1,3)-glucan remodeling.
abstract: The cell wall is essential for the yeast to hypha (Y-H) transition that enables Candida albicans to invade human tissues and evade the immune system. The main constituent, β(1,3)-glucan, is remodeled by glucanosyltransferases of the GH72 family. Phr1p is responsible of glucan remodeling at neutral-alkaline pH and is essential for morphogenesis and virulence. Due to the pH-regulated expression of PHR1, the phr1Δ phenotype is manifested at pH > 6 and its severity increases with the rise in pH. We exploited the pH-conditional nature of a PHR1 null mutant to analyze the impact of glucan remodeling on the hyphal transcriptional program and the role of chitin synthases in the hyphal wall stress (HWS) response.
  
  
  
  In hyphal growth inducing conditions, phr1Δ germ tubes are defective in elongation, accumulate chitin, and constitutively activate the signaling pathways mediated by the MAP kinases Mkc1p, Cek1p and Hog1p. The transcriptional profiles revealed an increase of transcript levels for genes involved in cell wall formation (CHS2 and CHS8, CRH11, PGA23, orf19.750, RBR1, RBT4, ECM331, PGA6, PGA13), protein N-glycosylation and sorting in the ER (CWH8 and CHS7), signaling (CPP1, SSK2), ion transport (FLC2, YVC1), stress response and metabolism and a reduced expression of adhesins. A transient up-regulation of DNA replication genes associated with entry into S-phase occurred whereas cell-cycle regulating genes (PCL1, PCL2, CCN1, GIN4, DUN1, CDC28) were persistently up-regulated. To test the physiological relevance of altered CHS gene expression, phr1Δ chsxΔ (x = 2,3,8) mutant phenotypes were analyzed during the Y-H transition. PHR1 deletion was synthetic lethal with CHS3 loss on solid M199 medium-pH 7.5 and with CHS8 deletion on solid M199-pH 8. On Spider medium, PHR1 was synthetic lethal with CHS3 or CHS8 at pH 8.
  
  
  
  The absence of Phr1p triggers an adaptive response aimed to reinforce the hyphal cell wall and restore homeostasis. Chs3p is essential in preserving phr1Δ cell integrity during the Y-H transition. Our findings also unveiled an unanticipated essential role of Chs8p during filamentation on solid media. These results highlight the flexibility of fungal cells in maintaining cell wall integrity and contribute to assessments of glucan remodeling as a target for therapy.
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, Via Celoria 26, 20133, Milano, Italy.
authors.forename: Genny
authors.initials: G
authors.lastname: Degani
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, Via Celoria 26, 20133, Milano, Italy.|Present address: Unit of Cell therapy and Cryobiology, Fondazione IRCCS Cà Granda, Ospedale Maggiore Policlinico, Milano, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Ragni
authors.affiliation: Unidad de Genómica, CAI de Genómica y Proteómica, UCM, Madrid, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: Botias
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, Via Celoria 26, 20133, Milano, Italy.|Present address: Evolva, Basel, Switzerland.
authors.forename: Davide
authors.initials: D
authors.lastname: Ravasio
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, Via Celoria 26, 20133, Milano, Italy.|Present address: Instituto de Biología Funcional y Genómica, Salamanca, Spain.
authors.forename: Julia
authors.initials: J
authors.lastname: Calderon
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, Via Celoria 26, 20133, Milano, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Pianezzola
authors.affiliation: Departamento de Microbiologia II, Facultad de Farmacia, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Jose Manuel
authors.initials: JM
authors.lastname: Rodriguez-Peña
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, Via Celoria 26, 20133, Milano, Italy.
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: Vanoni
authors.affiliation: Departamento de Microbiologia II, Facultad de Farmacia, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Arroyo
authors.affiliation: Department of Microbiology and Immunology, Georgetown University, Washington, D.C, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Fonzi
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, Via Celoria 26, 20133, Milano, Italy. Laura.Popolo@unimi.it.
authors.forename: Laura
authors.identifier: 0000-0002-5590-0167
authors.initials: L
authors.lastname: Popolo
mesh_terms: D002176:Candida albicans / Q000502:physiology*; D002473:Cell Wall / Q000378:metabolism*; D016000:Cluster Analysis; D004261:DNA Replication; D004843:Epistasis, Genetic; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D015966:Gene Expression Regulation, Fungal; D016681:Genome, Fungal; D023281:Genomics / Q000379:methods; D005936:Glucans / Q000378:metabolism*; D025301:Hyphae; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D013312:Stress, Physiological; D059467:Transcriptome
chemical_list: D005656:Fungal Proteins; D005936:Glucans; D008562:Membrane Glycoproteins; C091515:PHR1 protein, Candida albicans
keywords: Cell integrity; Cell wall; Chitin; Family GH72; Hyphal growth; MAP kinases; β(1,3)-glucan