Phospholipid homeostasis maintains cell polarity, development and virulence in metarhizium robertsii

The final product of the glycerol phosphate (GP) pathway is triacylglycerol (TAG) that regulates the homeostasis of energy, fatty acids and phospholipids in cells. The enzymes involved in this pathway have been characterized in many model organisms; however, their contributions to fungal infection are largely unclear. In this study, we performed serial deletion of genes in the GP pathway in the insect pathogenic fungus Metarhizium robertsii. The results indicated that a lysophosphatidate acyltransferase mrLPAAT1 was required for fungal growth, cell differentiation, maintenance of cell polarity and virulence. Lipidomic analysis indicated that deletion of mrLPAAT1 resulted in significant increases in TAG, fatty acids and phosphatidylcholine (PC) but decreased phosphatidic acid (PA), phosphatidylethanolamine (PE) and other species of phospholipids when compared to the wild type. Disruption of the isozymatic gene mrLPAAT2, however, resulted in a reduction in PC but not PA in the mutant cells. There were no changes in development and virulence in ΔmrLPAAT2. Phospholipid feeding assays verified that a PE supplement could rescue the cell differentiation defect in ΔmrLPAAT1. The results of this study reveal that cellular phospholipid homeostasis mediated by the GP pathway regulates fungal growth, cell polarity, differentiation and virulence.