Archive | 2019
Roles of the MAK-1 and MAK-2 MAP kinases modules in somatic cell fusion of filamentous fungi
Abstract
Cell fusion is essential for the development and propagation of most eukaryotic organisms. In the filamentous fungus Neurospora crassa, cell fusion is observed during early colony establishment, when germinating spores fuse into a supracellular network, which further develops into the highly interconnected mycelial colony. The interaction of these genetically identical germlings is mediated by an unusual signaling mechanism, in which, in order to avoid self-signaling, the cells take turns in signal sending and receiving. The switch between these two physiological states is represented by the alternating membrane recruitment of the SO protein and the MAP kinase MAK-2. This dialog-like behavior is observed until the cells establish physical contact, when MAK-2 and SO both accumulate at the contact area. At this stage a second MAP kinase, MAK-1, is also recruited to the cell contact area, that controls the subsequent steps of cell wall remodeling and membrane fusion. The main goal of this thesis was to further characterize the molecular functions of the MAP kinases MAK-2 and MAK-1. A specific focus was the investigation of the relationship between the activity of these kinases and their subcellular spatial and temporal dynamics, by using molecular genetics, protein mislocalization, chemical genetics and live cell imaging. The results revealed a strong correlation between the specific subcellular localization and the activation and activity of the MAK-2 MAP kinase. In addition, for the first time a functional link between the MAK-2 and SO dynamics was identified. Furthermore, this work revealed new functions of MAK-1 in organizing of the actin cytoskeleton in fusing cells by activation of the Rho-GTPase RAC-1, while MAK-2 was shown to regulate the subcellular localization of the mentioned factors. A second independent research project investigated the conservation of cell fusion in other filamentous fungi. This study revealed for the first-time that the oscillatory recruitment of the fusion proteins is fully conserved in another filamentous fungus, the grey mold Botrytis cinerea. When N. crassa and B. cinerea spores were mixed, interspecies interactions were readily observed indicating that both fungi share a common molecular language.