The membrane trafficking system is important for compartmentalization of the biosynthesis pathway and secretion of deoxynivalenol (DON) mycotoxin (a virulence factor) in Fusarium graminearum. Flippases are transmembrane lipid transporters and mediate a number of essential physiological steps of membrane trafficking, including vesicle budding, charging, and protein diffusion within the membrane. However, the roles of flippases in secondary metabolism remain unknown in filamentous fungi. Herein, we identified five flippases (FgDnfA, FgDnfB, FgDnfC1, FgDnfC2, and FgDnfD) in F. graminearum and established their specific and redundant functions in the development and pathogenicity of this phytopathogenic fungus. Our results demonstrate that FgDnfA is critical for normal vegetative growth while the other flippases are dispensable. FgDnfA and FgDnfD were found crucial for the fungal pathogenesis, and a remarkable reduction in DON production was observed in ΔFgDNFA and ΔFgDNFD. Deletion of the FgDNFB gene increased DON production to about 30 times that produced by the wild type. Further analysis showed that FgDnfA and FgDnfD have positive roles in the regulation of trichothecene (TRI) genes (TRI1, TRI4, TRI5, TRI6, TRI12, and TRI101) expression and toxisome reorganization, while FgDnfB acts as a negative regulator of DON synthesis. In addition, FgDnfB and FgDnfD have redundant functions in the regulation of phosphatidylcholine transport, and double deletion of FgDNFB and FgDNFD showed serious defects in fungal development, DON synthesis, and virulence. Collectively, our findings reveal the distinct and specific functions of flippase family members in F. graminearum and principally demonstrate that FgDnfA, FgDnfD, and FgDnfB have specific spatiotemporal roles during toxisome biogenesis.

中文翻译：

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Flippases在禾谷镰刀菌的发育，致病性和次级代谢中起特定但独特的作用。

膜运输系统对于分隔禾本科镰刀菌的生物合成途径和分泌脱氧雪腐酚（DON）霉菌毒素（一种致病因子）很重要。Flippases是跨膜脂质转运蛋白，可介导膜运输的许多基本生理步骤，包括囊泡发芽，带电和蛋白质在膜内扩散。但是，在丝状真菌中，脂肪酶在次级代谢中的作用仍然未知。在此，我们确定了五个flippases（FgDnfA，FgDnfB，FgDnfC1，FgDnfC2和FgDnfD）在禾谷镰刀菌并在这种植物病原真菌的发育和致病性中确立了其特定和多余的功能。我们的结果表明，FgDnfA对于正常的营养生长至关重要，而其他动物则不需要。发现FgDnfA和FgDnfD对真菌发病机理至关重要，并且在ΔFgDNFA和ΔFgDNFD中观察到DON产量显着降低。所述缺失FgDNFB基因提高生产DON与由野生型生产了约30倍。进一步分析表明，FgDnfA和FgDnfD在单端孢调控的积极作用（TRI）基因（TRI1，TRI4，TRI5，TRI6，TRI12和TRI101）的表达和毒素重组，而FgDnfB则是DON合成的负调节剂。此外，FgDnfB和FgDnfD在调节磷脂酰胆碱的转运中具有多余的功能，而FgDNFB和FgDNFD的双重缺失显示出真菌发育，DON合成和毒力方面的严重缺陷。总的来说，我们的发现揭示了禾谷镰刀菌中flippase家族成员的独特和特定功能，并且主要证明了FgDnfA，FgDnfD和FgDnfB在有毒生物发生期间具有特定的时空作用。