Studies of saltational evolution of the river-weed family, Podostemaceae, with unique adaptive morphologies

足茎科是一种水生被子植物，生长在河流或瀑布的岩石表面。它们在雨季经受湍急的水流，在旱季暴露在空气中。该科广泛分布于世界各地的泛热带地区。由于其独特的形态，自19世纪后期以来，足茎科植物受到了广泛的关注。最近利用cpDNA（例如mat K）进行的分子系统发育分析清楚地表明，Podostemaceae属于eudicaceae，与Classulaceae接近。因此，植物体的特殊形状似乎是适应独特栖息地的结果，即所谓的盐碱化进化。本研究旨在阐明菊科植物的进化历史及其突变机制。通过对非洲、马达加斯加、南美、亚洲等地的植物考察，收集了菊科植物属，并对菊科植物进行了发育比较、分子进化分析、分子遗传分析和am生理分析。系统发育分析表明，美洲、非洲和亚洲的狐尾草科均为单系群，分布范围狭窄且局地分布，而三尾草亚科（Tristicha trifaria）在美洲和非洲分布特别广泛。我们的研究表明，Tristicha trifaria起源于西非（喀麦隆），并分散到除亚洲以外的许多热带地区。另一方面，比较发育清楚地表明，Podostemoideae的茎尖分生组织（SAM）完全缺失，叶原基产生于与细胞发育迟缓和分离有关的老叶基。这个过程类似于细胞程序性死亡。另一个亚科，小叶蝉亚科，是小叶蝉亚科的姐妹科，具有典型的被子植物SAM，推测在小叶蝉亚科从三叶蝉亚科进化而来时SAM急剧缺失。为了研究SAM是否在形态学或遗传学上丢失，我们提取了STM同源-，WUS同源-和CLV3同源基因，其中三个基因在拟南芥（一种模式植物）的SAM中检测到。我们现在正在进行原位杂交的方法来检测这些同源基因在叶片原基形成的预期区域。生态生理结果表明，在距离水面20cm深度处，豆科扁平根或菌状根的光合活性最高，说明生长在水面附近的植物体受到了大量阳光的破坏。与生活在水中的其他浮游生物分享光合作用行为是很有趣的。有趣的是，在Podostemoideae中，表皮细胞有两种大小完全不同的叶绿体，即非常小的和非常大的。小的叶绿体位于表皮细胞的上壁附近，大的叶绿体位于细胞的下壁附近，两者并排排列，没有开放空间。似乎靠近上壁的小叶绿体充当了大量阳光的屏障。少

Podostemaceae is an aquatic angiosperm that is growing on the rock surface in the river or waterfall. They are subjected to rushing water in the rainy season and exposed in the air in the dry season. The family is widespread in pan-tropic regions all over the world. Because of their peculiar morphology, Podostemaceae plants have been paid much attention since the late 1800s. Recent molecular phylogenetic analyses using cpDNA (e.g. mat K) clearly shows that Podostemaceae belongs to the eudicots, and is close to Classulaceae. Therefore, the peculiar shape of plant body seems to have evolved as a result of adaptation to unique habitats, by so-called saltational evolution. We aimed to clarify the evolutionary history and the mechanism underlying the saltational evolution of Podostemaceae. We conducted botanical expeditions in Africa, Madagascar, South America, and Asia to collect genera of Podostemaceae, and examined them by the comparative development among Podostemaceae genera, the molec … More ular phylogenetic analysis, the molecular genetic analysis, and the am-physiological analysis. The Phylogenetic analysis showed that American, African and Asian Podostemaceae each form monophyletic groups, and their distributions are narrow and local In contrast, Tristicha trifaria (subfamily Tristichoideae) is exceptionally widespread through America and Africa. Our examination suggested that Tristicha trifaria was originated from West Africa (Cameroon), and dispersed to many tropical areas excluding Asia. On the other hand, comparative development clearly showed that the shoot apical meristem (SAM) is totally lacking in Podostemoideae, and leaf primordia arise from the older leaf base associated with cell retardation and separation. This process is similar to the programmed cell death. The other subfamily, Tritichoideae, sister to subfamily Podostemoideae, has SAM typical of angiosperms, and it is supposed that SAMs were missing drastically when Podostemoideae evolved from Tristichoideae. To examine whether the SAM was lost morphologically or genetically, we extracted STM homologous-, WUS homologous-, and CLV3 homologous-genes, three of which are detected in the SAMs of Arabidopsis (a model angiosperm plant). We are now carrying out the in situ hybridization method to detect those homologous genes in the expected area of leaf primordium formation. Eco-physiologically, it was shown that the photosynthetic activity of Podostemaceae flattened or thalloid roots was the highest in the depth of 20cm from the water surface, suggesting that the plant body growing near the water surface is damaged by extensive sunlight. It is interesting to share the photosynthetic behavior with other planktons that lives in water. The epidermal cells interestingly have two types of chloroplasts with quite different sizes, i.e. the very small and the very large ones, in Podostemoideae. The small chloroplasts are located near the upper wall in the epidermal cell, and the large near the bottom wall of the cell, both of which are located side by side with no open space. It seems likely that the small chloroplasts near the upper wall act as barrier of extensive sunlight. Less