Molecular bases of intra- and interspecies cell communication in filamentous fungi

• Applicant: Professor Dr. André Fleißner
• Subject Area: Plant Genetics and Genomics
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 406255916

Somatic cell fusion plays an important role for the development and propagation of filamentous fungi. In the red bread mold Neurospora crassa, for example, germinating spores mutually attract each other and fuse into a supracellular network that further develops into the mycelial colony. In the inner parts of mature colonies hyphal branches merge, thereby increasing the interconnectedness of the mycelium. Our earlier work identified an unusual cell communication mechanism employed by fusing spores. The two fusion partners take rapid turns in signal sending and receiving thereby establishing a kind of “cellular dialog”. On the molecular level, this mechanism involves the alternating recruitment of a MAP kinase module (MAK-2) and the fungus specific SO protein to the plasma membrane.Our current preliminary work focused on the molecular function of the SO protein. The obtained data indicate that SO interacts with a second MAP kinase signaling pathway (MAK-1), which is also essential for germling fusion and controls the organization of the actin cytoskeleton during tropic growth of the fusion partners. In addition, we identified a new factor interacting with SO (SIP-1). Interestingly SIP-1 localizes already to the tips of non-interacting germlings in an oscillating manner, indicating that the cells undergo cell-autonomous rapid switches between two physiological stages. Considering that germinating spores are the main mean of fungal infections, this observation is of broad significance.We furthermore showed that the cell dialog mechanism is highly conserved in the phytopathogenic grey mold Botrytis cinerea. Spores of N. crassa and B. cinerea even interact and establish physical contact, however, fail to undergo successful fusion. Interestingly we found that fusion and infectious growth are two alternative, mutually exclusive developmental routes in B. cinerea.The goals of the current projects include the description of the molecular functions of the SO and SIP-1 proteins, as well as their role within the known signaling network. A major focus is the interaction of both proteins with the MAK-1 MAP kinase pathway and the actin cytoskeleton. In addition, we will analyze the molecular basis of the cellular decision-making between fusion and infectious growth in B. cinerea and will decipher the mechanisms preventing interspecies fusion.In summary, the obtained data will greatly contribute to our understanding of eukaryotic cell-cell communication and fusion, fungal pathogenicity mechansims, and cellular self/non-self recognition.

• DFG Programme: Research Grants