Mutant alleles of the essential 14-3-3 gene in Candida albicans distinguish between growth and filamentation

Abstract

The opportunistic fungal pathogen Candida albicans has the ability to exploit diverse host environments and can either reside commensally or cause disease. In order to adapt to its new environment it must respond to new physical conditions, nutrient sources, and the host immune response. This requires the co-regulation of multiple signalling networks. The 14-3-3 family of proteins is highly conserved in all eukaryotic species. These proteins regulate signalling pathways involved in cell survival, the cell cycle, and differentiation, and effect their functions via interactions with phosphorylated serines/threonines. In C. albicans there is only one 14-3-3 protein, Bmh1p, and it is required for vegetative growth and optimal filamentation. In order to dissect separate functions of Bmh1p in C. albicans, site-directed nucleotide substitutions were made in the C. albicans BMH1 gene based on studies in other species. Putative temperature-sensitive, ligand-binding and dimerization mutants were constructed. In addition two mutant strains identified through random mutagenesis were analysed. All five mutant strains demonstrated varying defects in growth and filamentation. This paper begins to segregate functions of Bmh1p that are required for optimal growth and the different filamentation pathways. These mutant strains will allow the identification of 14-3-3 target interactions and correlate the individual functions of Bmh1p to cellular processes involved in pathogenesis.

Ustilago maydis Rho1 and 14-3-3 Homologues Participate in Pathways Controlling Cell Separation and Cell Polarity

“…For example, in S. cerevisiae, 14-3-3 homologues Bmh1/Bmh2 regulate pseudohypha formation through the MAPK pathway (38). 14-3-3 proteins have also been implicated in controlling filamentation in other dimorphic fungi, especially in C. albicans (37) and Y. lipolytica (16). In these organisms, the extent of filamentous growth is proportional to the level of 14-3-3 protein expression (16).…”

“…14-3-3 functions have been associated with filamentous or pseudohyphal growth in C. albicans (37) and Yarrowia lipolytica. In C. albicans (30) and Y. lipolytica (16), strains with mutations in 14-3-3 proteins either develop abnormal filaments or fail to differentiate completely.…”

“…These acidic proteins have been found in each cellular compartment and most organisms examined possess multiple isoforms: seven isoforms are found in mammals, and as many as fifteen isoforms have been identified in plants (31). Interestingly, the yeast Saccharomyces cerevisiae, the fruit fly, Drosophila melanogaster, and the nematode, Caenorhabditis elegans, each possess only two 14-3-3 isoforms (50), while Candida albicans contains a single isoform (37). They function typically by binding their particular ligands at phosphoserine or phosphothreonine residues (50).…”

Decreased expression of 14-3-3 inParacoccidioides brasiliensisconfirms its involvement in fungal pathogenesis

“…Additionally, 14-3-3 has been shown to be involved in the filamentation of other dimorphic fungi such as Candida albicans 42 and Yarrowia lipolytica. In these microorganisms, the filamentous growth is proportional to the level of expression of the 14-3-3 protein.…”

Role for Endosomal and Vacuolar GTPases in Candida albicans Pathogenesis

“…Filamentous growth was also stimulated by embedding C. albicans cells within a YPS agar matrix or sandwiching cells between two layers of YPS agar (11). Chlamydospores were induced on cornstarch-Tween agar (49).…”