Oxylipin distribution in Eremothecium

[摘要] English: In the early 1990's, Kock and co-workers discovered acetylsalicylic acid (ASA)-sensitive oxylipins in yeasts. It was also reported that the site of production of these compounds may serve as important targets to control fungal infections. In 2004, researchers exposed another function for these oxylipins �?they may act as lubricants during spore release from enclosed asci. Since oxylipin production in only a limited number of species representing Eremothecium was thus far studied, it became the aim of this project to further extend this study and to determine the type and distribution of 3- hydroxy (OH) oxylipins in the remaining species i.e. Eremothecium coryli, E. cymbalariae and E. gossypii. In addition, the possible functions of these oxylipins as well as ascospore shape and ornamentations were assessed. Finally, the antifungal activity of ASA was also investigated in this group of important plant pathogens as well as other yeasts. Eremothecium coryli is known to produce intriguing spindle-shaped ascospores with long and thin whip-like appendages. In this study, ultra structural studies using scanning electron microscopy, indicate that these appendages serve to coil around themselves and around ascospores causing spore aggregation. Furthermore, using immunofluoresence confocal laser scanning microscopy it was found that hydrophobic 3-OH oxylipins cover the surfaces of these ascospores. Using gas chromatography-mass spectrometry, only the oxylipin 3-OH 9:1 (a monounsaturated fatty acid consisting of a hydroxyl group on carbon 3) could be identified. Sequential digital imaging suggests that oxylipin-coated spindle-shaped ascospores are released from enclosed asci probably by protruding through an already disintegrating ascus wall. Using immunofluorescence microscopy and 3-OH oxylipin specific antibodies, it was possible to map the presence of these compounds also in other Eremothecium species. In E. cymbalariae, these oxylipins were found to cover mostly the spiky tips of narrowly triangular ascospores while in E. gossypii, oxylipins covered the whole spindle-shaped ascospore with terminal appendages. The presence of these oxylipins was confirmed by chemical analysis. When ASA, a 3-OH oxylipin inhibitor, was added to these yeasts in increasing concentrations, the sexual stage was found to be the most sensitive. Results suggest that 3-OH oxylipins, produced by mitochondria through incomplete β-oxidation, are associated with the development of the sexual stages in both yeasts. Strikingly, preliminary studies on yeast growth suggest that yeasts, characterized by mainly an aerobic respiration rather than a fermentative pathway, are more sensitive to ASA than yeasts characterized by both pathways. These data further support the role of mitochondria in sexual as well as asexual reproduction of yeasts and its role to serve as target for ASA antifungal action.

[发布机构] University of the Free State