尽管孢子的进化对陆地上植物的多样化至关重要,对于模型植物,例如Physcomitriumpatens,孢子发生的特征不完全。在这项研究中,P.patens孢子发生的完整过程从胶囊扩张到成熟孢子形成,重点是复杂孢子壁和近端孔的构造。二倍体(孢子体)和单倍体(孢子)细胞都有助于孢子的发育和成熟。在胶囊扩张期间,胶囊的二倍体细胞,包括孢子母细胞(SMC),内囊壁层(孢子囊),还有小柱,贡献一个包含孢子个体发育的机械和营养的局部纤维状基质。新生孢子被封闭在第二基质中,所述第二基质被薄的SMC壁包围并悬浮在所述小室材料中。随着它们的扩展和分离,在三部分薄片的薄基础层的外部产生外膜带。致密的小球在整个小室中均匀地聚集,并且这些逐渐结合到孢子表面上以形成外壁外部的perine。在远端孢子表面,内部形式,而多刺的perine装饰被组装。外泌体至少部分起源于异类,而perine完全来自孢子外。穿过极地孢子的近端表面,一个孔在孢子发育开始时开始形成,由一个扩大的内部组成,一个环,和一个带有辐射纤维的中央垫。该复杂的孔是弹性的并且使得近侧孢子表面能够在被压缩(凹形)和膨胀(圆形)之间循环。除了提供取水和发芽的场所外,弹性孔可能与干燥耐受性有关。根据目前的系统发育,祖先的植物孢子有一个孔,exine,intine,还有Perine.艾草和耳草孢子的还原进化导致两组中的紫铜损失和艾草的孔径损失。这项研究为与其他植物群体进行比较以及未来研究跨植物孢子的发育遗传学和进化奠定了基础。
Although the evolution of spores was critical to the diversification of plants on land, sporogenesis is incompletely characterized for model plants such as Physcomitrium patens. In this study, the complete process of P. patens sporogenesis is detailed from capsule expansion to mature spore formation, with emphasis on the construction of the complex spore wall and proximal
aperture. Both diploid (sporophytic) and haploid (spores) cells contribute to the development and maturation of spores. During capsule expansion, the diploid cells of the capsule, including spore mother cells (SMCs), inner capsule wall layer (spore sac), and columella, contribute a locular fibrillar matrix that contains the machinery and nutrients for spore ontogeny. Nascent spores are enclosed in a second matrix that is surrounded by a thin SMC wall and suspended in the locular material. As they expand and separate, a band of exine is produced external to a thin foundation layer of tripartite lamellae. Dense globules assemble evenly throughout the locule, and these are incorporated progressively onto the spore surface to form the perine external to the exine. On the distal spore surface, the intine forms internally, while the spiny perine ornamentation is assembled. The exine is at least partially extrasporal in origin, while the perine is derived exclusively from outside the spore. Across the proximal surface of the polar spores, an
aperture begins formation at the onset of spore development and consists of an expanded intine, an annulus, and a central pad with radiating fibers. This complex
aperture is elastic and enables the proximal spore surface to cycle between being compressed (concave) and expanded (rounded). In addition to providing a site for water intake and germination, the elastic
aperture is likely involved in desiccation tolerance. Based on the current phylogenies, the ancestral plant spore contained an
aperture, exine, intine, and perine. The reductive evolution of liverwort and hornwort spores entailed the loss of perine in both groups and the aperture in liverworts. This research serves as the foundation for comparisons with other plant groups and for future studies of the developmental genetics and evolution of spores across plants.