Overexpression of Candida albicans EPT1 Alters Cell Wall Composition and Hyphal Length

Candida albicans is a leading cause of systemic bloodstream infections inimmunocompromised patients and phospholipid biosynthesis is an important requirement for this organism to grow and cause disease. We have previously demonstrated that the psd1?/? psd2?/? mutant, which cannot synthesize the phospholipid phosphatidylethanolamine (PE) by the CDP- DAG pathway, is avirulent in the mouse model of systemic candidiasis and has decreased cytotoxicity against oral epithelial cells in vitro. Similarly, an ept1?/? mutant, which cannot produce PE by the Kennedy pathway, exhibits decreased kidney fungal burden in systemically infected mice and has decreased epithelial cell cytotoxicity in vitro. Conversely, overexpression of EPT1 results in a hypervirulent phenotype both in vivo and in vitro. However, the mechanism by which hypervirulence is driven by overexpression of Ept1 remains unknown. In the present study RNA sequencing was performed to elucidate this mechanism. In addition, we sought to identify transcriptional dysregulation that occurs in mutants deficient for PE biosynthesis to elucidate why these mutants have decreased virulence. It was found that decreased PE synthesis leads to down-regulation of genes involved in the TCA cycle, glycolysis, amino acid biosynthesis, and fatty acid oxidation, which may indicate that there are issues with mitochondrial function. Furthermore, significant increases in transcription of glycosylation machinery genes were observed in this mutant, which may reflect the substantial cell wall defects that this mutant exhibits. There were no transcriptional differences between the EPT1 overexpression strain and the wild-type besides an increase in EPT1, indicating that the hypervirulent phenotype is a consequence of post-transcriptional changes. Upon further analysis it was found that overexpression of EPT1 causes increased chitin content, resistance to caspofungin induced ß-1,3-glucan exposure, and increased hyphal length. These findings mayexplain the previously observed hypervirulence of this strain.