Abstract
Candida albicans cell wall is important for growth and interaction with the environment. RLM1 is one of the putative transcription factors involved in the cell wall integrity pathway, which plays an important role in the maintenance of the cell wall integrity. In this work we investigated the involvement of RLM1 in the cell wall biogenesis and in virulence. Newly constructed C. albicans Δ/Δrlm1 mutants showed typical cell wall weakening phenotypes, such as hypersensitivity to Congo Red, Calcofluor White, and caspofungin (phenotype reverted in the presence of sorbitol), confirming the involvement of RLM1 in the cell wall integrity. Additionally, the cell wall of C. albicans Δ/Δrlm1 showed a significant increase in chitin (213%) and reduction in mannans (60%), in comparison with the wild-type, results that are consistent with cell wall remodelling. Microarray analysis in the absence of any stress showed that deletion of RLM1 in C. albicans significantly down-regulated genes involved in carbohydrate catabolism such as DAK2, GLK4, NHT1 and TPS1, up-regulated genes involved in the utilization of alternative carbon sources, like AGP2, SOU1, SAP6, CIT1 or GAL4, and genes involved in cell adhesion like ECE1, ALS1, ALS3, HWP1 or RBT1. In agreement with the microarray results adhesion assays showed an increased amount of adhering cells and total biomass in the mutant strain, in comparison with the wild-type. C. albicans mutant Δ/Δrlm1 strain was also found to be less virulent than the wild-type and complemented strains in the murine model of disseminated candidiasis. Overall, we showed that in the absence of RLM1 the modifications in the cell wall composition alter yeast interaction with the environment, with consequences in adhesion ability and virulence. The gene expression findings suggest that this gene participates in the cell wall biogenesis, with the mutant rearranging its metabolic pathways to allow the use of alternative carbon sources.
Highlights
The yeast cell wall is an essential cellular structure for the osmotic stabilization, protection against mechanical damage, maintenance of cell shape, adhesion, and invasive growth [1]
Since C. albicans RLM1 mutants did not show any of the phenotypes described for S. cerevisiae cell wall integrity (CWI) mutants, the sensitivity of the deleted strains to a range of cell wall-perturbing agents, as well as to compounds known to be associated with altered cell walls, was determined
Deletions of several S. cerevisiae genes involved in the cell wall integrity pathway such as BCK1, MKK1, MKK2 or SLT2/MPK1 confer typical phenotypes, such as failure to grow at elevated temperatures in the absence of an osmostabilizer; sensitivity to caffeine in the medium; failure to grow on glycerol medium; and sensitivity to nitrogen starvation [33,34,35,36,37]
Summary
The yeast cell wall is an essential cellular structure for the osmotic stabilization, protection against mechanical damage, maintenance of cell shape, adhesion, and invasive growth [1] It consists of a matrix of b-glucan, chitin and mannoproteins, surrounding the plasma membrane. The response to cell wall damage is well understood from studies with the budding yeast Saccharomyces cerevisiae, where the PKC-MAPK pathway is the major cell wall responsive regulatory system in stress conditions and during cell wall biogenesis This pathway comprises the sensors Mid and Wsc in the plasma membrane which, upon cell wall damage, interact with the GDP/GTP exchange factor Rom, leading to the conversion of the G protein Rho to its activated GTP-bound state. The calcineurin and high-osmolarity pathways have been shown to participate in the response to cell wall damages
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