Genetic and Molecular Dissection of Hyphal Anastomosis

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Intellectual Merit Filamentous fungi are the primary degraders of plant cellulosic material in the environment. Different species of filamentous fungi are associated with the roots of almost all plant species in a symbiotic relationship that allows plants to gain micronutrients from soil. In addition, other species are disease causing agents in plants, or cause important human diseases. All of these filamentous fungi, both beneficial and pathogenic species, grow by tip extension, branching and hyphal fusion to form a hyphal network. The formation of the hyphal network is believed to be essential for transfer of nutrients throughout ecosystems by root associated and saprophytic fungi and for colony establishment and exploitation of resources in pathogenic fungi. Although tip growth and branching have been extensively studied in filamentous fungi, little is known about the mechanism of hyphal fusion or the function of the hyphal network. Live cell imaging and genetic analysis of hyphal fusion in the model filamentous fungus, Neurospora crassa have revealed that the process of hyphal fusion is a complex and carefully regulated biological process. A large number of components essential for hyphal fusion have been identified in N. crassa, including components of signal transduction pathways, polarization components, filamentous fungal specific proteins and transmembrane proteins. Hyphal fusion mutants show developmental defects, in addition to slower growth rates and/or lag phase to reach maximal growth rate. These observations indicate that the formation of an interconnected network in filamentous fungi is essential for both exploitation of an environmental niche and for developmental processes. The objectives of this research are to dissect the process of germling/hyphal fusion using a combination of live cell imaging, genetic analysis and biochemical tools to elucidate the mechanisms of self-signaling, polarization and membrane merger with the ultimate goal of understanding the role of hyphal networks in ecosystems, symbiosis and pathogenesis. Broader Impact: Hyphal fusion in filamentous fungi is comparable to cell fusion events between genetically identical cells in other organisms, such as cell-cell fusion resulting in syncytia, such as myoblast fusion during muscle differentiation, trophoblast fusion during placental development and between osteoclasts during bone formation. Thus, studying cell-cell fusion in N. crassa provides a useful model for understanding molecular mechanisms of cell fusion events in more complex eukaryotic species. This project provides excellent training projects for undergraduate, graduate students and post-doctoral associates. A number of undergraduate California Opportunity Scholars have been recruited to this project; these students come from disadvantaged backgrounds and low performing schools in the Bay Area.