Oxylipin production and novel ascospore release mechanisms in the yeast Dipodascus

[摘要] English: Certain ascomycetous yeasts produce lubricated 3-hydroxy (3-OH) oxylipin-coated, micron-scalesexual spores in a variety of shapes, sizes, colors and sometimes with nano-scale surfaceornamentations. In past literature, these oxylipin-coated ornamentations are only mentioned for use inclassification and no thought was given to their possible purpose or function. These 3-OH oxylipinswere found to be associated with the sheathed ascospores of some species representing the genusDipodascus. However, these compounds have not yet been studied in detail in this genus. In addition,no thought was given to the mystery behind the release mechanics of sheathed ascospores fromenclosing bottle-shaped asci and the role of these 3-OH oxylipins during dispersal. Therefore, itbecame the aim in this study to determine 3-OH oxylipin structure, distribution and function in D.albidus UOFS Y-1445T and D. geniculatus UOFS Y-1144 and to reveal the secrets behind the releasemechanics of sheathed ascospores from bottle-shaped asci in these two species. Using electronmicroscopy, confocal laser scanning microscopy, gas chromatography-mass spectrometry (GC-MS)and digital live imaging, the release mechanisms of ascospores of various lengths from bottle-shapedasci, and produced by different yeasts, are compared in this study. It was found that Dipodascusalbidus produces oval ascospores that are surrounded by compressible, oxylipin-coated sheathsenabling ascospores to slide past each other when forced by turgor pressure and by possible sheathcontractions towards the narrowing ascus-neck. Usually elongated ascospores, as found inDipodascopsis uninucleata var. uninuc/eata, are linked by means of oxylipin-coated interlocked hookedridges on the surfaces of neighbouring ascospores, thereby keeping them aligned while being pushedtowards the ascus-tip by turgor pressure. Interestingly, it was uncovered in this study that Dipodascusgeniculatus produce elongated, oxylipin-coated sheathed ascospores that are effectively released frombottle-shaped asci without alignment. This is possible because the ascus neck and opening have thesame diameter as the length of the ascospore, thus allowing the ascospores to turn sideways withoutblocking the ascus upon release. Interestingly, it was found that increased concentrations ofacetylsalicylic acid (ASA), inhibit both ascospore release and 3-OH oxylipin production in these yeasts, thereby implicating this oxylipin in sexual reproduction. Using GC-MS analysis, the oxylipin wascharacterized as a3-OH metabolite. The same mass spectrum, implicating the presence of the same3-0H oxylipin structure, was found to be present in other Dipodascus species. This implicates that this3-0H metabolite might be conserved on genus level.

[发布机构] University of the Free State