Cells rarely exist alone, which drives the evolution of diverse mechanisms for identifying and responding appropriately to the presence of other nearby cells. Filamentous fungi depend on somatic cell-to-cell communication and fusion for the development and maintenance of a multicellular, interconnected colony that is characteristic of this group of organisms. The filamentous fungus Neurospora crassa is a model for investigating the mechanisms of somatic cell-to-cell communication and fusion. N. crassa cells chemotropically grow toward genetically similar cells, which ultimately make physical contact and undergo cell fusion. Here, we describe the development of a Pprm1-luciferase reporter system that differentiates whether genes function upstream or downstream of a conserved MAP-Kinase (MAPK) signaling complex by using a set of mutants required for communication and cell fusion. The vast majority of these mutants are deficient for self-fusion and for fusion when paired with wild type cells. However, the ham-11 mutant is unique in that fails to undergo self-fusion, but chemotropic interactions and cell fusion are restored in ham-11 + wild-type interactions. In genetically dissimilar cells, chemotropic interactions are regulated by genetic differences at doc-1 and doc-2, which regulate pre-fusion non-self recognition; cells with dissimilar doc-1 and doc-2 alleles show greatly reduced cell fusion frequencies. Here, we show that HAM-11 functions in parallel with the DOC-1 and DOC-2 proteins to regulate activity of the MAPK signaling complex. Together our data support a model of integrated self and non-self recognition processes that modulate somatic cell-to-cell communication in N. crassa.

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Integration of Self and Non-self Recognition ... - genetics.org