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

盆栽是一种水生被子植物，生长在河流或瀑布的岩面上。它们在雨季受到急流的影响，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。自19世纪末以来，狼毒草科植物因其独特的形态而备受关注。最近利用cpDNA(如mat K)进行的分子系统发育分析清楚地表明，狼毒草科属于优生科，与文冠花科相近。因此，植物身体的特殊形状似乎是由于适应独特的生境而进化的，也就是所谓的盐生进化。本研究旨在阐明盆栽属植物的进化史和救赎进化的机制。我们在非洲、马达加斯加、南美洲和亚洲进行了植物学考察，收集了香附科的属，并对它们进行了比较研究，比较了香附科各属之间的发育关系，并对它们进行了比较研究，结果表明，香附子属(Molec….)更多的是系统发育分析、分子遗传分析和非生理分析。系统发育分析表明，美洲、非洲和亚洲的Podostemaceae均为单系群，分布范围窄且具有地方性，而Tristicha trifaria(Tristichoideae亚科)在美洲和非洲分布尤为广泛。我们的研究表明，Tristicha trifaria起源于西非(喀麦隆)，并散布到除亚洲以外的许多热带地区。另一方面，比较发育表明，顶端分生组织(SAM)在Podostemoideae中完全缺乏，叶原基是由较老的叶基产生的，与细胞延迟和分离有关。这一过程类似于细胞程序性死亡。另一个亚科是短柄藻亚科的姊妹亚科，具有被子植物的SAM特征，推测当短柄藻亚科从短柄藻亚科进化而来时，短柱亚科的SAM基因已经严重缺失。为了检测SAM是在形态上还是在遗传上丢失，我们提取了STM同源基因、WUS同源基因和CLV3同源基因，其中三个基因在拟南芥(一种模式被子植物)的SAM中被检测到。我们现在正在进行原位杂交的方法来检测那些在预期的叶原基形成区域中的同源基因。生理生态研究结果表明，香蒲根的光合作用活性在距水面20 cm处最高，说明生长在水面附近的植物体内受到了强烈的光照伤害。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截然不同的叶绿体，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底壁附近，两者并排分布，没有开放的空间。看起来很可能是靠近上壁的小叶绿体起到了遮挡广泛阳光的作用。较少

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