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Isolation and characterization of YlBEM1, a gene required for cell polarization and differentiation in the dimorphic yeast Yarrowia lipolytica.

ABSTRACT: The ability to switch between a unicellular yeast form and different filamentous forms (fungal dimorphism) is an important attribute of most pathogenic fungi. Dimorphism involves a series of events that ultimately result in dramatic changes in the polarity of cell growth in response to environmental factors. We have isolated and characterized YlBEM1, a gene encoding a protein of 639 amino acids that is essential for the yeast-to-hypha transition in the yeast Yarrowia lipolytica and whose transcription is significantly increased during this event. Cells with deletions of YlBEM1 are viable but show substantial alterations in morphology, disorganization of the actin cytoskeleton, delocalization of cortical actin and chitin deposition, multinucleation, and loss of mating ability, thus pointing to a major role for YlBEM1 in the regulation of cell polarity and morphogenesis in this fungus. This role is further supported by the localization of YlBemlp, which, like cortical actin, appears to be particularly abundant at sites of growth of yeast, hyphal, and pseudohyphal cells. In addition, the potential involvement of YlBem1p in septum formation and/or cytokinesis is suggested by the concentration of a green fluorescent protein-tagged version of this protein at the mother-bud neck during the last stages of cell division. Interestingly, overexpression of MHY1, YlRAC1, or YlSEC31, three genes involved in filamentous growth of Y. lipolytica, induced hyphal growth of bem1 null mutant cells.

SUBMITTER: Hurtado CA

PROVIDER: S-EPMC118001 | biostudies-literature | 2002 Aug

REPOSITORIES: biostudies-literature

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Isolation and characterization of YlBEM1, a gene required for cell polarization and differentiation in the dimorphic yeast Yarrowia lipolytica.

Hurtado Cleofe A R CA Rachubinski Richard A RA

Eukaryotic cell 20020801 4

The ability to switch between a unicellular yeast form and different filamentous forms (fungal dimorphism) is an important attribute of most pathogenic fungi. Dimorphism involves a series of events that ultimately result in dramatic changes in the polarity of cell growth in response to environmental factors. We have isolated and characterized YlBEM1, a gene encoding a protein of 639 amino acids that is essential for the yeast-to-hypha transition in the yeast Yarrowia lipolytica and whose transcr ...[more]

PMID: 12456001

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Project description:The yeast Yarrowia lipolytica undergoes a morphological transition from yeast-to-hyphal growth in response to environmental conditions. A forward genetic screen was used to identify mutants that reliably remain in the yeast phase, which were then assessed by whole-genome sequencing. All the smooth mutants identified, so named because of their colony morphology, exhibit independent loss of DNA at a repetitive locus made up of interspersed ribosomal DNA and short 10- to 40-mer telomere-like repeats. The loss of repetitive DNA is associated with downregulation of genes with stress response elements (5'-CCCCT-3') and upregulation of genes with cell cycle box (5'-ACGCG-3') motifs in their promoter region. The stress response element is bound by the transcription factor Msn2p in Saccharomyces cerevisiae We confirmed that the Y. lipolyticamsn2 (Ylmsn2) ortholog is required for hyphal growth and found that overexpression of Ylmsn2 enables hyphal growth in smooth strains. The cell cycle box is bound by the Mbp1p/Swi6p complex in S. cerevisiae to regulate G1-to-S phase progression. We found that overexpression of either the Ylmbp1 or Ylswi6 homologs decreased hyphal growth and that deletion of either Ylmbp1 or Ylswi6 promotes hyphal growth in smooth strains. A second forward genetic screen for reversion to hyphal growth was performed with the smooth-33 mutant to identify additional genetic factors regulating hyphal growth in Y. lipolytica Thirteen of the mutants sequenced from this screen had coding mutations in five kinases, including the histidine kinases Ylchk1 and Ylnik1 and kinases of the high-osmolarity glycerol response (HOG) mitogen-activated protein (MAP) kinase cascade Ylssk2, Ylpbs2, and Ylhog1 Together, these results demonstrate that Y. lipolytica transitions to hyphal growth in response to stress through multiple signaling pathways.IMPORTANCE Many yeasts undergo a morphological transition from yeast-to-hyphal growth in response to environmental conditions. We used forward and reverse genetic techniques to identify genes regulating this transition in Yarrowia lipolytica We confirmed that the transcription factor Ylmsn2 is required for the transition to hyphal growth and found that signaling by the histidine kinases Ylchk1 and Ylnik1 as well as the MAP kinases of the HOG pathway (Ylssk2, Ylpbs2, and Ylhog1) regulates the transition to hyphal growth. These results suggest that Y. lipolytica transitions to hyphal growth in response to stress through multiple kinase pathways. Intriguingly, we found that a repetitive portion of the genome containing telomere-like and rDNA repeats may be involved in the transition to hyphal growth, suggesting a link between this region and the general stress response.

Dataset Information

Isolation and characterization of YlBEM1, a gene required for cell polarization and differentiation in the dimorphic yeast Yarrowia lipolytica.

Publications

Isolation and characterization of YlBEM1, a gene required for cell polarization and differentiation in the dimorphic yeast Yarrowia lipolytica.

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