Interplay between Self and Non-self recognition mechanisms in Neurospora crassa

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With the evolution of multicellularity various challenges arise. The extreme degree of cooperation essential for multicellular existence requires a maximum of coordination and communication between cells. One critical feature for interacting cells in a wide range of organisms is the ability to distinguish self from non-self. Without seeing or hearing their surroundings, cells must be able to sense their environment to attract possible interaction partners or avoid potential risks. The mammalian immune system is only one of many examples for the basic necessity for non-self recognition mechanisms in multicellular organisms. In microbes the molecular basis of non-self recognition is still not fully understood. The filamentous fungus Neurospora crassa is a model organism with many genomic and genetic tools with which to investigate the molecular basis of non-self recognition in eukaryotic microbes. This organism has long been used to study heterokaryon incompatibility as one mechanism to restrict the propagation of fusion products between genetically dissimilar individuals by inducing programmed cell death. We identified non-self recognition mechanisms in N. crassa germlings that are much more sophisticated than initially anticipated. In fact, the fungus uses three layers of non-self recognition to avoid fusion between non-self germlings. (1) It is able to recognize non-self individuals from a distance and to avoid attraction before two non-self cells fuse. (2) After attraction and contact of some non-self cells cell wall breakdown (which is the first step of cell fusion) does not occur. (3) A cell death reaction is induced within minutes after two non-self cells fuse with each other. This is the first time that these non-self recognition mechanisms are observed in germlings of filamentous fungi. This research will identify the genes responsible for the observed phenotypes using bulked segregant analyses in combination with next generation sequencing. The corresponding genes will be functionally characterized. The experiments described in this proposal will provide the basis for a new field of research in non-self recognition in filamentous fungi and which is applicable to attraction, fusion and non-self recognition in other eukaryotic species as well.