The putative histone-like transcription factor FgHltf1 is required for vegetative growth, sexual reproduction, and virulence in Fusarium graminearum.

The target of rapamycin (TOR) signaling pathway plays critical roles in regulating vegetative development and virulence in Fusarium graminearum. Previously, we have demonstrated that the putative type 2A phosphatase FgPpg1, a downstream component of the pathway, is important for hyphal growth, sporulation, DON biosynthesis and virulence. Here, we report the identification of FgHLTF1 putatively encoding a histone-like transcription factor by the transcriptome analysis of an ΔFgppg1 mutant. The FgHLTF1 expression was significantly down-regulated by the deletion of FgPPG1 or treatment with rapamycin. Analysis of an F. graminearum strain expressing green fluorescent protein (GFP) revealed that FgHltf1-GFP fusion protein mainly localized to the nucleus. Targeted gene deletion mutants of FgHLTF1 exhibited a significant reduction in vegetative growth, sexual reproduction and virulence. Moreover, the growth of the ΔFghltf1 mutants was restricted by hyperosmotic stresses. Unlike the wild-type strain, the mutants showed anomalous subcellular translocation of FgHog1-GFP under hyperosmotic conditions, suggesting that FgHLTF1 is associated with the high osmolarity glycerol response pathway. Taken together, we conclude that FgHLTF1 is transcriptionally regulated by the TOR signaling pathway and plays important roles in regulating vegetative growth, sexual reproduction, virulence and hyperosmotic stresses in F. graminearum.