Characterization of the Neurospora crassa Cell Fusion Proteins, HAM-6, HAM-7, HAM-8, HAM-9, HAM-10, AMPH-1 and WHI-2

Abstract

Intercellular communication of vegetative cells and their subsequent cell fusion is vital for different aspects of growth, fitness, and differentiation of filamentous fungi. Cell fusion between germinating spores is important for early colony establishment, while hyphal fusion in the mature colony facilitates the movement of resources and organelles throughout an established colony. Approximately 50 proteins have been shown to be important for somatic cell-cell communication and fusion in the model filamentous fungus Neurospora crassa. Genetic, biochemical, and microscopic techniques were used to characterize the functions of seven previously poorly characterized cell fusion proteins. HAM-6, HAM-7 and HAM-8 share functional characteristics and are proposed to function in the same signaling network. Our data suggest that these proteins may form a sensor complex at the cell wall/plasma membrane for the MAK-1 cell wall integrity mitogen-activated protein kinase (MAPK) pathway. We also demonstrate that HAM-9, HAM-10, AMPH-1 and WHI-2 have more general functions and are required for normal growth and development. The activation status of the MAK-1 and MAK-2 MAPK pathways are altered in mutants lacking these proteins. We propose that these proteins may function to coordinate the activities of the two MAPK modules with other signaling pathways during cell fusion.

Revitalization of a Forward Genetic Screen Identifies Three New Regulators of Fungal Secondary Metabolism in the Genus Aspergillus

“…The AN5169 protein shares 30% percent identity with the Ham-9 protein described in Neurospora crassa. Conforming to A. nidulans genetic nomenclature, we refer to it as HamI (43). Ham-9 appears to regulate cross-communication of the mitogen-activated protein kinase (MAPK) pathways in N. crassa and is required for hyphal fusion (43).…”

“…Conforming to A. nidulans genetic nomenclature, we refer to it as HamI (43). Ham-9 appears to regulate cross-communication of the mitogen-activated protein kinase (MAPK) pathways in N. crassa and is required for hyphal fusion (43). The hamI gene encodes an 858-aminoacid (aa) protein containing two conserved domains: a sterile alpha motif (SAM), which is a potential protein-protein interaction domain in scaffold proteins, and a pleckstrin homology-like (PH) domain, which is typically responsible for targeting a protein to the appropriate cellular location (Fig.…”

“…The hamI gene encodes an 858-aminoacid (aa) protein containing two conserved domains: a sterile alpha motif (SAM), which is a potential protein-protein interaction domain in scaffold proteins, and a pleckstrin homology-like (PH) domain, which is typically responsible for targeting a protein to the appropriate cellular location (Fig. 1E) (43,74,75). Deletion of hamI results in reduction, but not elimination, of NOR production, while complementation of the hamI point mutant results in an increase in NOR production (Fig.…”

“…In N. crassa, HAM proteins are involved with cell-to-cell fusion or hyphal anastomosis, which is a requirement for asexual and sexual development (43). Several studies have shown that Aspergillus utilizes the endomembrane system for production and transport of the "aflatoxisomes" that function to compartmentalize several of the enzymatic steps leading to production of this toxin (58,59).…”

Mating-type genes and hyphal fusions in filamentous basidiomycetes

“…Importantly, MAK-2 kinase was shown to phosphorylate the N-terminus of MOB-3, which could lead, with the help of HAM-2 and HAM-3 associations to the transport and accumulation of MAK-1 kinase into the nucleus to activate the CWI pathway regulating transcription factors. N. crassa hyphal fusion mutants also include the genes encoding transcription factors ADV-1, ADA-3, RCO-1, SNF5 and PP1 (Fu et al, 2011a(Fu et al, , 2014Leeder et al, 2013). These transcription factors are possibly needed to activate genes involved in cell communication and hyphal growth in CATs and hyphal fusions .…”