A novel STRIPAK complex component mediates hyphal fusion and fruiting‐body development in filamentous fungi

Summary The STRIPAK complex is involved in growth, cell fusion, development and signaling pathways, and thus malfunctions in the human STRIPAK complex often result in severe neuronal diseases and cancer. Despite the high degree of general conservation throughout the complex, several STRIPAK complex‐associated small coiled‐coil proteins of animals and yeasts are not conserved across species. As there are no data for filamentous ascomycetes, we addressed this through affinity purification with HA‐tagged striatin ortholog PRO11 in Sordaria macrospora. Combining the method with liquid chromatography‐mass spectrometry, we were able to co‐purify STRIPAK complex interactor 1 (SCI1), the first STRIPAK‐associated small coiled‐coil protein in filamentous ascomycetes. Using yeast two‐hybrid experiments, we identified SCI1 protein regions required for SCI1‐PRO11 interaction, dimerization of SCI1 and interaction with other STRIPAK components. Further, both proteins PRO11 and SCI1 co‐localize with the nuclear basket protein SmPOM152 at the nuclear envelope. Expression of the gene sci1 occurs during early developmental stages of S. macrospora, and the protein SCI1 in combination with PRO11 is required for cell fusion, vegetative growth and sexual development. The results of the present study will help to understand the underlying molecular mechanisms of STRIPAK signaling and function in cellular development and diseases in higher eukaryotes. The STRIPAK complex is involved in growth, cell fusion, development and signaling pathways of animals and fungi. SCI1, a small coiled‐coil protein, is part of the fungal STRIPAK complex and interacts with the striatin ortholog PRO11 and the SLMAP ortholog PRO45. The data of the present study indicate the presence of spatial‐temporal STRIPAK complexes in filamentous fungi, tightly regulating cell differentiation and thus sexual development.