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Functional variability in adhesion and flocculation of yeast megasatellite genes
Cyril Saguez1,2, David Viterbo1, Stéphane Descorps-Declère1,3
1Institut Pasteur, Université Paris Cité, CNRS UMR3525, Genétique des Génomes, Paris F-75015, France.
Abstract:
Megasatellites are large tandem repeats found in all fungal genomes but especially abundant in the opportunistic pathogen Candida glabrata. They are encoded in genes involved in cell-cell interactions, either between yeasts or between yeast and human cells. In the present work, we have been using an iterative genetic system to delete several Candida glabrata megasatellite-containing genes and found that 2 of them were positively involved in adhesion to epithelial cells, whereas 3 genes negatively controlled adhesion. Two of the latter, CAGL0B05061g or CAGL0A04851g, were also negative regulators of yeast-to-yeast adhesion, making them central players in controlling Candida glabrata adherence properties. Using a series of synthetic Saccharomyces cerevisiae strains in which the FLO1 megasatellite was replaced by other tandem repeats of similar length but different sequences, we showed that the capacity of a strain to flocculate in liquid culture was unrelated to its capacity to adhere to epithelial cells or to invade agar. Finally, to understand how megasatellites were initially created and subsequently expanded, an experimental evolution system was set up, in which modified yeast strains containing different megasatellite seeds were grown in bioreactors for more than 200 generations and selected for their ability to sediment at the bottom of the culture tube. Several flocculation-positive mutants were isolated. Functionally relevant mutations included general transcription factors as well as a 230-kbp segmental duplication.
Insights
Megasatellites, large repeats in fungal genomes, significantly impact Candida glabrata's cell adhesion. Genetic studies reveal specific megasatellite genes controlling yeast-to-epithelial and yeast-to-yeast interactions.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Megasatellites are large tandem repeats prevalent in fungal genomes, particularly abundant in Candida glabrata.
- These repeats are encoded in genes associated with cell-cell interactions, including yeast-host and yeast-yeast interactions.
Purpose of the Study:
- To investigate the role of megasatellite-containing genes in Candida glabrata adhesion.
- To explore the relationship between megasatellite sequences and flocculation/adhesion properties.
- To understand the evolutionary mechanisms of megasatellite creation and expansion.
Main Methods:
- Iterative genetic system to delete megasatellite-containing genes in Candida glabrata.
- Construction of synthetic Saccharomyces cerevisiae strains with altered megasatellite sequences.
- Experimental evolution in bioreactors over 200 generations to select for flocculation-positive mutants.
Main Results:
- Two megasatellite genes positively regulate adhesion to epithelial cells; three genes negatively regulate it.
- Two specific genes (CAGL0B05061g, CAGL0A04851g) negatively regulate both epithelial and yeast-to-yeast adhesion.
- Flocculation in liquid culture is independent of epithelial cell adhesion or agar invasion.
- Experimental evolution identified mutations in transcription factors and segmental duplications linked to increased flocculation.
Conclusions:
- Megasatellite genes play crucial, distinct roles in regulating Candida glabrata adhesion.
- The capacity for flocculation is separable from epithelial adhesion, suggesting different underlying mechanisms.
- Megasatellite expansion can be driven by mutations in general transcription factors and chromosomal duplications.
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