Effect of the developmental protein PRO11 and its interaction partners on fruiting-body development and hyphal fusion of Sordaria macrospora

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Fruiting bodies are the most complex three-dimensional structures formed by filamentous ascomycetes. They enclose the sexual spores and are composed of many different cell types which are differentiated from vegetative hyphae. Fusion of vegetative hyphae seems to be a prerequisite for fruiting-body development. Many genes which are essential for hyphal fusion are also involved in the regulation of fruiting-body development. By complementing fruiting-body mutants of the model fungus Sordaria macrospora we were able to isolate genes which are equally important for both processes. The focus of this project is the conserved development protein PRO11, a homolog of proteins of the mammalian striatin family. In mammals, striatin proteins have been identified as central scaffolding proteins of the striatin interacting phosphatase and kinase (STRIPAK) complex. Striatin proteins are regulatory subunits of the phosphatase PP2A and link phosphatase PP2A to kinases of the germinal center (GC) III family and additional conserved proteins. Apparently, the STRIPAK complex regulates the phosphorylation and de-phosphorylation of target proteins which are involved in signal transduction pathways required for hyphal fusion and fruiting-body development. During the first funding period we were able to demonstrate that the striatin homolog PRO11 together with previously identified developmental proteins is a central component of a STRIPAK complex in S. macrospora. This includes SmMOB3, a putative kinase activator, PRO22, a striatin interacting protein, and PP2AA, the scaffolding subunit of protein phosphatase 2A. In mammals, the cellular function of the STRIPAK complex is unknown. In contrast, functional analysis using knockout mutants with distinct developmental defects revealed a role of the fungal STRIPAK complex during hyphal fusion and fruiting-body development. The aim of this proposal is the functional characterization of these interaction partners und to define their role during hyphal fusion and fruiting-body development. This will give us crucial insights to understand conserved mechanisms for cell fusion and multicellular differentiation not only in fungi but also in higher eukaryotes.