Candida albicans CaPTC6 is a functional homologue for Saccharomyces cerevisiae ScPTC6 and encodes a type 2C protein phosphatase

The phosphatase Ptc6 is involved in virulence and MAPK signalling in Fusarium oxysporum

Mitogen-activated kinase (MAPK) signalling pathways are involved in several important processes related to the development and virulence of Fusarium oxysporum. Reversible phosphorylation of the protein members of these pathways is a major regulator of essential biological processes. Among the phosphatases involved in dephosphorylation of MAPKs, type 2C protein phosphatases (PP2Cs) play important roles regulating many developmental strategies and stress responses in yeasts. Nevertheless, the PP2C family is poorly known in filamentous fungi. The F. oxysporum PP2C family includes seven proteins, but only Ptc1 has been studied so far. Here we show the involvement of Ptc6 in the stress response and virulence of F. oxysporum. Expression analysis revealed increased expression of ptc6 in response to cell wall and oxidative stresses. Additionally, targeted inactivation of ptc6 entailed enhanced susceptibility to cell wall stresses caused by Calcofluor White (CFW). We also demonstrate that the lack of Ptc6 deregulates both the Mpk1 phosphorylation induced by CFW and, more importantly, the Fmk1 dephosphorylation induced by pH acidification of the extracellular medium, indicating that Ptc6 is involved in the regulation of these MAPKs. Finally, we showed, for the first time, the involvement of a phosphatase in the invasive growth and virulence of F. oxysporum.

RNA sequencing reveals an additional Crz1-binding motif in promoters of its target genes in the human fungal pathogen Candida albicans

Background

The calcium/calcineurin signaling pathway is mediated by the transcription factors NFAT (nuclear factor of activated T cells) in mammals and Crz1 (calcineurin-responsive zinc finger 1) in yeasts and other lower eukaryotes. A previous microarray analysis identified a putative Crz1-binding motif in promoters of its target genes in Candida albicans, but it has not been experimentally demonstrated.

Methods

An inactivation mutant for CaCRZ1 was generated through CRISPR/Cas9 approach. Transcript profiling was carried out by RNA sequencing of the wild type and the inactivation mutant for CaCRZ1 in response to 0.2 M CaCl₂. Gene promoters were scanned by the online MEME (Multiple Em for Motif Elicitation) software. Gel electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) analysis were used for in vitro and in vivo CaCrz1-binding experiments, respectively.

Results

RNA sequencing reveals that expression of 219 genes is positively, and expression of 59 genes is negatively, controlled by CaCrz1 in response to calcium stress. These genes function in metabolism, cell cycling, protein fate, cellular transport, signal transduction, transcription, and cell wall biogenesis. Forty of these positively regulated 219 genes have previously been identified by DNA microarray analysis. Promoter analysis of these common 40 genes reveals a consensus motif [5′-GGAGGC(G/A)C(T/A)G-3′], which is different from the putative CaCrz1-binding motif [5′-G(C/T)GGT-3′] identified in the previous study, but similar to Saccharomyces cerevisiae ScCrz1-binding motif [5′-GNGGC(G/T)CA-3′]. EMSA and ChIP assays indicate that CaCrz1 binds in vitro and in vivo to both motifs in the promoter of its target gene CaUTR2. Promoter mutagenesis demonstrates that these two CaCrz1-binding motifs play additive roles in the regulation of CaUTR2 expression. In addition, the CaCRZ1 gene is positively regulated by CaCrz1. CaCrz1 can bind in vitro and in vivo to its own promoter, suggesting an autoregulatory mechanism for CaCRZ1 expression.

Conclusions

CaCrz1 differentially binds to promoters of its target genes to regulate their expression in response to calcium stress. CaCrz1 also regulates its own expression through the 5′-TGAGGGACTG-3′ site in its promoter.

Ser/Thr protein phosphatases in fungi: structure, regulation and function

Reversible phospho-dephosphorylation of proteins is a major mechanism for the control of cellular functions. By large, Ser and Thr are the most frequently residues phosphorylated in eukar-yotes. Removal of phosphate from these amino acids is catalyzed by a large family of well-conserved enzymes, collectively called Ser/Thr protein phosphatases. The activity of these enzymes has an enormous impact on cellular functioning. In this work we pre-sent the members of this family in S. cerevisiae and other fungal species, and review the most recent findings concerning their regu-lation and the roles they play in the most diverse aspects of cell biology.

The putative transient receptor potential channel protein encoded by the orf19.4805 gene is involved in cation sensitivity, antifungal tolerance, and filamentation in Candida albicans

Transient receptor potential (TRP) channels, an ancient family of cation channels, are highly conserved in eukaryotes and play various physiological functions, ranging from sensation of ion homeostasis to reception of pain and vision. Calcium-permeable TRP channels have been identified from the plant Arabidopsis thaliana (AtCsc1) and the budding yeast Saccharomyces cerevisiae (ScCsc1). In this study, we characterized the functions of the Csc1 homolog, orf19.4805, in Candida albicans. Orf19.4805 is a protein of 866 amino acids and 11 transmembrane domains, which shares 49% identity (69% similarity) in amino acid sequence with ScRsn1. Here, we demonstrate that deletion of the orf19.4805 gene causes C. albicans cells to be sensitive to SDS (sodium dodecyl sulfate) and antifungal drugs, and tolerance to zinc, manganese, and cadmium ions. Candida albicans cells lacking orf19.4805 show a defect in filamentation in vitro. Therefore, orf19.4805 is involved in the regulation of cation homeostasis and filamentation in C. albicans.

Type 2C protein phosphatases in fungi

Type 2C Ser/Thr phosphatases are a remarkable class of protein phosphatases, which are conserved in eukaryotes and involved in a large variety of functional processes. Unlike in other Ser/Thr phosphatases, the catalytic polypeptide is not usually associated with regulatory subunits, and functional specificity is achieved by encoding multiple isoforms. For fungi, most information comes from the study of type 2C protein phosphatase (PP2C) enzymes in Saccharomyces cerevisiae, where seven PP2C-encoding genes (PTC1 to -7) with diverse functions can be found. More recently, data on several Candida albicans PP2C proteins became available, suggesting that some of them can be involved in virulence. In this work we review the available literature on fungal PP2Cs and explore sequence databases to provide a comprehensive overview of these enzymes in fungi.