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The ham-2 locus, encoding a putative transmembrane protein, is required for hyphal fusion in Neurospora crassa
Qijun Xiang1, Carolyn Rasmussen, N Louise Glass
1Plant and Microbial Biology Department, University of California, Berkeley, California 94720-3102, USA.
Abstract:
Somatic cell fusion is common during organogenesis in multicellular eukaryotes, although the molecular mechanism of cell fusion is poorly understood. In filamentous fungi, somatic cell fusion occurs during vegetative growth. Filamentous fungi grow as multinucleate hyphal tubes that undergo frequent hyphal fusion (anastomosis) during colony expansion, resulting in the formation of a hyphal network. The molecular mechanism of the hyphal fusion process and the role of networked hyphae in the growth and development of these organisms are unexplored questions. We use the filamentous fungus Neurospora crassa as a model to study the molecular mechanism of hyphal fusion. In this study, we identified a deletion mutant that was restricted in its ability to undergo both self-hyphal fusion and fusion with a different individual to form a heterokaryon. This deletion mutant displayed pleiotropic defects, including shortened aerial hyphae, altered conidiation pattern, female sterility, slow growth rate, lack of hyphal fusion, and suppression of vegetative incompatibility. Complementation with a single open reading frame (ORF) within the deletion region in this mutant restored near wild-type growth rates, female fertility, aerial hyphae formation, and hyphal fusion, but not vegetative incompatibility and wild-type conidiation pattern. This ORF, which we named ham-2 (for hyphal anastomosis), encodes a putative transmembrane protein that is highly conserved, but of unknown function among eukaryotes.
Insights
Researchers identified ham-2, a gene crucial for hyphal fusion in filamentous fungi like Neurospora crassa. This discovery sheds light on the molecular mechanisms underlying cell fusion in these organisms.
Area of Science:
- Mycology
- Cell Biology
- Genetics
Background:
- Somatic cell fusion is vital for organogenesis in eukaryotes, but its molecular mechanisms remain largely unknown.
- Filamentous fungi exhibit somatic cell fusion during vegetative growth, forming a network of hyphae through anastomosis.
Purpose of the Study:
- To investigate the molecular mechanisms of hyphal fusion in the filamentous fungus Neurospora crassa.
- To identify genes involved in regulating hyphal fusion and associated developmental processes.
Main Methods:
- Generation and analysis of a deletion mutant in Neurospora crassa.
- Complementation studies to identify the responsible gene.
- Phenotypic characterization of the mutant and complemented strains.
Main Results:
- A deletion mutant exhibited defects in hyphal fusion, aerial hyphae formation, fertility, and growth rate.
- Complementation with the ham-2 gene restored hyphal fusion, fertility, and aerial hyphae formation.
- The ham-2 gene encodes a conserved transmembrane protein potentially involved in cell fusion.
Conclusions:
- The ham-2 gene plays a significant role in regulating hyphal fusion in Neurospora crassa.
- Understanding ham-2 function can provide insights into conserved eukaryotic cell fusion mechanisms.