Molecular and Genetic Dissection of Hyphal Anastomosis

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Filamentous fungi grow by tip extension, branching and hyphal fusion to form a hyphal network that makes up a fungal individual. Although tip growth and branching have been extensively studied in filamentous fungi, essentially nothing is known about the mechanism of hyphal fusion or the function of the formation of a hyphal network. Studies by this laboratory on the hyphal fusion process using live cell imaging and confocal microscopy in the filamentous fungus, Neurospora crassa, have revealed a complex and carefully regulated biological process with obvious consequences to the fungal individual. Hyphal fusion is a way to increase cytoplasmic flow and interconnectedness of hyphae, which may be important in intra-hyphal communication that influences hyphal pattern formation and developmental processes. Hyphal fusion in filamentous fungi is comparable to cell fusion events in other organisms, such as fertilization events between egg and sperm and somatic cell fusion events that result in syncytia, such as myoblast fusion during muscle differentiation. The hyphal fusion process must be carefully regulated because inappropriate cell wall breakdown would result in lysis of the hyphae. N. crassa is the best filamentous fungus to assess the process and function of hyphal fusion in filamentous fungi because of its tractability for live cell imaging techniques (http://www.neurospora.com/), full genome sequence information (http://www-genome.wi.mit.edu/annotation/fungi/neurospora/), the availability of hyphal fusion mutants, and the ease of genetic and molecular techniques. Preliminary results indicate that a series of signaling events are required for hyphal fusion, one of which is mediated by a map kinase pathway. Hyphal fusion mutants show physiological and developmental defects, suggesting that the failure to form a hyphal network has physiological consequences. The objectives of this project are to characterize hyphal fusion mutants using a combination of live cell imaging via confocal microscopy, and genetic and biochemical analysis to elucidate the mechanism of self-signaling, polarization and membrane fusion. The ultimate goal is to understand how the formation of the hyphal network allows a fungal individual to perform the physiological and developmental processes required to complete its life cycle. Understanding the hyphal fusion process in filamentous fungi will not only reveal the function of the formation of the hyphal network, but will provide a model for cell fusion events in other eukaryotic organisms.