Silene latifolia and Microbotryum violaceum : Molecular, cellular and Morphological studies on plant sexuality and parasitic fungus operating it.

用黑穗病菌侵染黑穗病菌（Microbotryum violaceum），诱导雌雄异株植物银叶（Silene latifolia）雌花发育雄性器官。健康雌花的雄蕊只生长到第6期，而受感染雌花的雄蕊则发育到成熟期（第12期），此时雄蕊充满真菌的端孢子而不是花粉粒。利用自然扫描电子显微镜、诺玛斯基干涉显微镜和荧光显微镜，研究了黑穗病菌寄生对寄主植物的形态改变以及黑穗病菌丝在花蕾中的定位。感染植株花的持续时间明显长于健康植株，这可能是由于感染强化了花基部和花药花丝等花器官。侵染植物幼芽的所有器官均可见黑穗病菌丝，包括萼片、花瓣、雄蕊和雌蕊原基。在健康的雌花中，花药启动了孢子细胞的形成，但缺乏壁细胞层。相比之下，感染雌花的壁细胞层分化为绒毡层、中间细胞层和内膜层，与健康雄花的花药一样。侵染花药的黑穗病孢子形成始于产孢细胞之间的细胞间区，导致过早产孢细胞、绒毡层组织和中间细胞层的退化。感染后的花药内胚层和表皮的发育形态正常。为了研究寄主与寄生虫之间的相互作用，在高压冷冻法固定后，用电子显微镜观察了受感染雌花的幼芽和真菌诱导的花药。利用这种方法，我们发现这种真菌的寄生菌丝含有几个细胞外囊泡，并且在第8阶段具有一致的外观。在这一阶段，寄生菌丝被观察到与被感染雌花药中垂死的孢子细胞相邻。在第9阶段，观察到死亡和垂死的孢子细胞数量增加，其中真菌的孢子菌丝发育并形成初始的端孢子。在这个阶段，在一些真菌附近存在几种类型的电子密集材料。银蛋白染色显示，最初的端孢子含有两种液泡，真菌细胞壁含有丰富的碳水化合物。产孢细胞可能对真菌的感染很敏感，导致破坏。此外，真菌在花药中加速细胞死亡，并利用死亡宿主细胞的成分形成成熟的端孢子。银叶是一种雌雄异株植物，其性别由X和Y染色体决定。利用原位杂交技术检测拟南芥中与pistilllata （P1）同源的b功能基因SLM2的表达。SLM2在被抑制的雌花雄蕊中不表达，但在侵染黑穗病的雌花发育雄蕊中表达。这些结果表明，SLM2的控制与Y染色体的存在无关。黑穗病感染的雌性为阐明b功能基因与性别决定因素之间的关系提供了一个有用的系统。少

The development of male organs is induced in female flowers of the dioecious plant Silene latifolia by infection with the smut fungus Microbotryum violaceum. Stamens in a healthy female flower grow only to stage 6, whereas those in an infected female flower develop to the mature stage (stage 12), at which the stamens are filled with fungal teliospores instead of pollen grains.Using natural scanning electron microscopy, Nomarski interference microscopy, and fluorescence microscopy, we investigated the morphological modifications of the host plant resulting from this parasitism and the localization of smut hyphae in the flower bud. Flowers of infected plants lasted significantly longer than those of healthy plants, probably because the infection strengthened floral organs, such as the flower base and the anther filaments. Smut hyphae were observed throughout all organs of the young flower buds of infected plants, including sepals, petals, stamens, and pistil primordia. In healthy female … More flowers, anthers initiated sporogenous cell formation, but lacked parietal cell layers. By contrast, the parietal cell layers of infected female flowers differentiated into tapetal tissue, middle cell layers, and endothecial layers, as in the anthers of healthy male flowers. Smut spore formation in the infected anther was initiated in intercellular regions between the sporogenous cells, resulting in degeneration of premature sporogenous cells, tapetal tissue, and middle cell layers. The development of the endothecial layers and epidermis in the infected anther were morphologically normal.To investigate these host-parasite interactions, young floral buds and fungus-induced anthers of infected female flowers were examined by electron microscopy following fixation by a high-pressure freezing method. Using this approach, we found that parasitic hyphae of this fungus contain several extracellular vesicles and have a consistent appearance up to stage 8. At that stage, parasitic hyphae are observed adjacent to dying sporogenous cells in the infected female anther. At stage 9, an increased number of dead and dying sporogenous cells is observed, among which the sporogenous hyphae of the fungus develop and form initial teliospores. Several types of electron-dense material are present in proximity to some fungi at this stage. The initial teliospores contain two types of vacuoles, and the fungus cell wall contains abundant carbohydrate, as revealed by silver protein staining. The sporogenous cell is probably sensitive to infection by the fungus, resulting in disruption. In addition, the fungus accelerates cell death in the anther and utilizes constituents of the dead host cell to form the mature teliospore.Silene latifolia is a dioecious plant in which sex is determined by X and Y chromosomes. Expression of the B-function gene SLM2, an ortholog of PISTILLATA (P1) in Arabidopsis, was examined by in situ hybridization. SLM2 was not expressed in suppressed stamens of female flowers, but was expressed in developing stamens of smut-infected female flowers. These results indicate that the control of SLM2 is independent of the presence of the Y chromosome. Smut-infected females provide a useful system for clarifying the relationship between the B-function gene and the sex determination factor. Less