Diversity of spore morphology among fission yeasts.

Fungi produce spores as a strategy for survival and dispersal. Spore shape and surface structure are thought to facilitate adhesion to hosts or vectors, and the outermost spore layer is associated with spore hydrophobicity and stress tolerance. Although the morphology of Schizosaccharomyces pombe spores has been well characterized-including a distinctive bumpy surface and an outermost proteinaceous layer-spore morphology in other fission yeasts remains poorly understood. Here we compared the structure of spores from four fission yeast species-S. pombe, S. octosporus, S. japonicus, and S. versatilis-using various microscopy techniques. Optical and electron microscopy revealed that the surface structures of fission yeast spores differ markedly among species. Notably, the fibrillar surface structures observed in S. pombe spores are absent in other fission yeast spores. Ultrathin-section electron microscopy showed that the characteristic electron-dense structures of the outermost spore layer in S. pombe are also largely absent in the other species. Among the four species examined, S. pombe spores exhibited the highest stress tolerance to heat and ethanol. Collectively, these results suggest that fission yeasts have acquired distinct spore morphologies, which may have contributed to their adaptation to diverse habitats.