Studies on the origin of angiosperms and the evolution of ovules

1.摘要为了解被子植物原始胚珠的形态特征，对木兰科大玉兰的胚珠进行了形态学分析。外层被毛形成一个帽状结构，然后变成杯状，在被毛间隙间的索上有一个外生物。在属于原始目的三科的胚珠中，在奥地利和蒂莫尼亚，外皮是帽状的，而在Illicium是普遍的。综合其他原始被子植物的资料和被子植物的系统发育关系，推测原始胚珠为倒生胚珠，外被呈帽状，与侧生器官叶相似。为了更好地了解原始被子植物胚珠和被的基因同源性，我们分析了YABBY家族基因同源物的表达模式，这些基因参与决定外侧器官的背面性。NaINO是一种INO同源物，从睡莲科睡莲属植物中分离出来，在睡莲的外被外层表达。结果表明，外皮可能是与叶片同源的侧生器官。AmbF1是YABBY2的同源物，从Amborella中分离出来，在叶片背侧组织和地毯内部组织中表达，其模式与模式植物拟南芥（Arabidopsis thaliana）的模式不同。这些结果不符合广泛接受的假设，即心皮是一个重复的叶片或一个由叶柄叶衍生的海鞘结构。综上所述，我们推测被子植物特有的外被由叶片等侧面器官产生并分化，而控制侧面器官特异性的YABBY家族同源基因NaINO和AmbF1的进化及其表达模式的改变与被子植物的起源和分化有关。

1.A morphological analysis of ovules of Magnolia grandiflora, Magnoliaceae, was performed in order to understand the morphology of the primitive ovule of angiosperms. The outer integument arose as a hood-shaped structure and then became cupular with an outgrowth arising on the funiculus between a gap in the integument. In the ovules of three families assigned to the primitive order Austrobaileyales, the outer integument is hood-shaed in Austrobaileya and Ttimernia, while it is copular in Illicium. Taking in account data of other primitive angiosperms and phylogenetic relationships of angiosperms, it is inferred that the primitive ovule is the anatropous one with the hood-shaped outer integument, which is similar to the lateral organ leaf.2.In order to better understand the homology of the ovule and that of the integument of primitive angiosperms at gene level, expression patterns were analyzed for homologues of genes of the YABBY family, which are involved in determination of the dorsiventrality of lateral organs. NaINO, an INO homologue, isolated from Nymphaea, Nymphaeaceae, was expressed in the outer layer of the outer integument. The result suggested that the outer integument may be a lateral organ homologous to the leaf. AmbF1, a YABBY2 homologue, isolated from Amborella, was expressed in the dorsal tissue of the leaf and the inner tissue of the carpet, patterns distinct from those of the advanced eudicot Arabidopsis thaliana, a model plant. These results are not in accordance with the widely accepted hypotheses that the carpel is a con duplicate leaf or an ascidiate structure derived from a peltate leaf.3.In conclusion, it is inferred the outer integument unique to angiosperms arose from a lateral organ such as the leaf and then diversified, and NaINO and AmbF1 homologous to YABBY family genes that govern the specificity of lateral organs evolved and their expression patterns changed in association with the origin and diversification of angiosperms.