Functional, transcriptomic, and lipidomic studies of the choC gene encoding a phospholipid methyltransferase in Aspergillus fumigatus

Phosphatidylcholines (PCs) are a class of cell membrane phospholipids playing important roles in cellular integrity and signaling. In eukaryotes, PCs are biosynthesized via the Kennedy cytidine nucleotide and the Bremer-Greenberg pathways. The Aspergillus choC gene is predicted to encode a phospholipid methyltransferase, the key enzyme in the latter pathway. In this study, we have characterized choC in the opportunistic human pathogenic fungus Aspergillus fumigatus and show that ChoC plays a vital role in the endogenous biosynthesis of PC, which is necessary for proper vegetative growth, development, cell viability, and cell wall integrity of the fungus. Transcriptomic analyses have revealed that the deletion (Delta) of choC leads to the differential expression of diverse genes related to PC biosynthetic pathways, G protein signaling pathways, cell cycle, and autophagy. Importantly, the Delta choC mutant averted cell death and regained cellular proliferation by regulating the expression of different PC synthesis genes after 4 days of incubation. Lipidomic analyses have demonstrated that Delta choC directly leads to decreased PC synthesis, thereby affecting the length and unsaturation of PC fatty acid chains. In addition, Delta choC leads to disturbed metabolism of other lipids, such as reduced phosphatidylethanolamine and neutral lipid triacylglycerol, but increased diacylglycerol amounts. Murine infection studies showed that invasive pathogenicity of the Delta choC spores was significantly weakened coupled with a drastic reduction of their ability to colonize in kidneys. In summary, ChoC plays central roles in PC biosynthesis, lipid metabolism, cell membrane/wall integrity, endoplasmic reticulum function, and pathogenicity in A. fumigatus, implying that ChoC can be a novel target for antifungal therapy.