MoLcb3 contributes to sphingolipid balance and stress responses in Magnaporthe oryzae

Abstract:

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid notable for its involvement in the regulation of biological processes and the development of diseases. Sphingosine-1-phosphate phosphatase (S1PP) plays a role in regulating the intracellular metabolism of S1P, while the biological roles of S1PP in plant pathogenic fungi have not been reported. [Objective] To explore the role of S1PP in the morphological differentiation, pathogenic process, and maintenance of sphingolipid balance of Magnaporthe oryzae. [Methods] We employed homologous recombination to delete the S1PP gene MoLCB3 from M. oryzae and characterized the obtained mutant ΔMolcb3 was by phenotypic analysis, gene complementation, and lipid metabolomics. Furthermore, we deleted the sphingosine kinase (SK) gene MoLcb4 from ΔMolcb3 to explore the relationship between MoLcb3 and MoLcb4. [Results] The deletion of MoLCB3 resulted in significant decreases in the mycelial growth rate and spore production and affected conidial malformation and initial appressorium formation. ΔMolcb3 completely lost the pathogenicity to barley. Moreover, the ΔMolcb3 mutant were significantly different from the wild type in responding to hyperosmic stress, cell wall integrity stress, high temperature stress, and fungal lipid synthesis inhibitors triadimefon and myriocin, suggesting that MoLcb3 was involved in these stress responses and lipid anabolism. Interestingly, the double mutant ΔMolcb3ΔMolcb4 basically compensated for all phenotypic defects of ΔMolcb3. In addition, lipid metabolomics showed that compared with the wild type, ΔMolcb3 presented significantly different levels of lipids, such as free fatty acids, ceramides, and phosphatidyl inositol. [Conclusion] MoLcb3 plays an important role in the mycelial growth, sporulation, spore germination, pathogenicity, stress responses, and lipid homeostasis. In addition, knockout of MoLCB4 can cushion the effects of MoLcb3 deletion. The results of this study provide new ideas for elucidating the sphingolipid metabolic pathway of M. oryzae and the development of inhibitors of fungal lipid biosynthesis.