AoMbp1 interacts with AoSwi6 and regulates hyphal development, stress tolerance, trap morphogenesis, and pathogenicity in Arthrobotrys oligospora

Abstract

The APSES family proteins, specific to fungi, regulate growth, development, and various biological processes. As a typical nematode-trapping fungus, Arthrobotrys oligospora has been extensively studied to understand the mechanism of trap formation. In this study, AoMbp1, an ortholog of the Saccharomyces cerevisiae APSES-type transcription factor Mbp1, was functionally characterized in A. oligospora. Aombp1 inactivation caused severe defects in mycelial growth and development. Specifically, the ∆Aombp1 mutant exhibited significantly reduced growth, increased hyphal septation and lipid droplet accumulation, and a marked decrease in nuclear numbers. Moreover, it showed substantially reduced conidiophore production and spore yield, along with abnormal spore morphology. Sensitivity to various chemical stressors, particularly hyperosmotic agents, was heightened, whereas trap formation and nematode predation ability were significantly impaired. The traps lost their original three-dimensional structure and adopted a planar shape. Further, RNA sequencing, DNA affinity purification sequencing, and yeast two-hybrid assays revealed that AoMbp1 interacts with AoSwi6, another APSES protein. Together, they participate in regulating the cell cycle, meiosis, lipid metabolism, and DNA replication and repair. Collectively, these findings clarify the role and underlying mechanisms of Mbp1 in mycelial development and trap morphogenesis in nematode-trapping fungi.