Assembly and Function of the Yeast Spore Wall

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All cells surround themselves with an extracellular matrix that provides both physical support and protection for the cell. In multicellular organisms the extracellular matrices from individual cells combine to form much larger structures that provide the scaffolding for the body of the organism. It is important, therefore, to understand how extracellular matrices are constructed and connected. The formation of the spore wall, a stratified, multicellular extracellular matrix, in the yeast Saccharomyces cerevisiae provides an excellent model system to study the assembly of extracellular matrices. An initial characterization of a collection of mutants defective in spore wall formation has provided an outline of the pathway of spore wall assembly. This initial work will be expanded by further studies on the role of the different spore wall assembly genes in promoting formation of the wall. The localization and activity of the beta-glucan and chitin syntheses, which catalyze the formation of the major spore wall polysaccharides, will be investigated both in wild type cells and in cells mutant for putative regulatory genes. Additionally, the molecular mechanism of action of the AMA1 gene, which links the exit from meiosis to the onset of spore wall formation will be explored. Finally, the outer layers of the spore wall both allow the spore to resist environmental stress and connect individual spores together through bridges. The targeting and anchoring to the spore wall of proteins involved in the assembly of these layers will be investigated. Also, a collection of mutants with modest defects in outer spore wall assembly will be analyzed to define genes involved in acquisition of resistance to specific stresses. In sum, these studies should deepen our understanding of the molecular mechanisms of spore wall construction, which will in turn provide insight into the strategies of extracellular matrix assembly in other organisms.