Building the Spore Wall:
The spore wall imparts most of the spore's resistance to environmental stress. After prospore membrane closure, the cell builds the spore wall in the lumen between the two membranes derived from the prospore membrane. The mature wall consists of four distinct layers: one predominantly of mannoproteins (mannan layer); one of beta-1,3 linked glucose residues (glucan layer); one of alpha 1,4 linked glucosamine residues (chitosan layer); and a layer of indeterminant structure whose major constituent is cross-linked tyrosine dimers (dityrosine layer).
Figure: Electron micrograph of an ascus containing mature spores. The spore wall material (SW) is formed in the lumen of the prospore membrane compartment (PrM). The inner, electron lucent layers of mannan and glucan are distinguishable from the outer, darker chitosan and dityrosine layers.
The layers of the spore wall are arranged, from innermost to outermost as follows: mannan, glucan, chitosan, and dityrosine. Mannans and glucans are also found in the vegetative cell wall. Chitosan and dityrosine are unique to the spore.
Figure: Fluorescence micrographs showing the temporal order of spore wall formation. The polysaccharides visualized are mannan (green), glucan (red), and chitosan (blue). At later time points both glucan and chitosan signals are lost due to the maturation of the outermost dityrosine layer.
The precise temporal order of assembly suggests that communication between the interior and the exterior of the cell is necessary to ensure proper construction of the wall.
| For More Details on our work in this area see references #7, #13, #14 |
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Additional Reading: Wagner, M., Briza, P., Pierce, M., & E. Winter (1999) Distinct steps in yeast spore morphogenesis require distinct SMK1 MAP kinase thresholds. Genetics. 151:1327-1340. [PubMed]
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