Patterns and Mechanisms of Ovule Diversification

胚珠作为种子发育的前体，是种子植物的一个重要特征，在种子的有性繁殖过程中起着至关重要的作用。无子植物是种子植物的主要类群，胚珠种类繁多，在珠被数量(外部鞘结构)和珠孔方向(珠被上的开口有利于受精)上表现出差异。胚珠多样性在被子植物的进化研究中具有不可估量的价值，胚珠发育成为研究植物形态发生遗传调控的有用模型。将使用跨学科的方法来描述胚珠进化的历史模式及其分子遗传学基础。卵形特征将被绘制在被子植物最好的可用系统发育图上，以阐明原始胚珠特征和衍生胚珠特征之间的转换。具有原始胚珠特征或衍生胚珠特征的物种将被选用于表型和分子遗传学特征。对珠被数量和珠孔方向变化基础的分子遗传分析将通过分析INO的同源基因来完成。INO基因在拟南芥中调节这些过程，并在外珠被中特异表达。从关键物种中分离INO同源基因，并对表达模式进行表征，将使形成和检验胚珠多样化的分子遗传变化假说成为可能。为了便于将来对胚珠多样化的研究，我们还将分离ATS，这是拟南芥外珠被和内珠被发育分离所必需的基因。拟议工作的完成将为植物发育的调控、胚珠多样化及其相互关系提供见解。

As the developmental precursors to seeds, ovules are a defining feature ofseed plants and play essential roles in their sexual reproduction. Amongangiosperms, the dominant group of seed plants, ovules are diverse,exhibiting differences in the number of integuments (external sheathingstructures), and in the orientation of the micropyle (the opening in theinteguments which facilitates fertilization). Ovule diversity has beeninvaluable in evolutionary studies of angiosperms, and ovule developmenthas become a useful model for studies on genetic regulation of plantmorphogenesis. An interdisciplinary approach will be used to characterize the historicalpatterns of ovule evolution and its molecular genetic basis. Ovulecharacteristics will be plotted onto the best available phylogenies forangiosperms to clarify transitions between primitive and derived ovulefeatures. Species having either primitive or derived ovule features willbe selected for phenotypic and molecular genetic characterization.Molecular genetic analysis of the basis of changes in integument number andmicropyle orientation will be accomplished through analysis of orthologs ofINO, a gene which regulates these processes in Arabidopsis and which isspecifically expressed in the outer integument. Isolation of INO orthologsfrom key species, and characterization of expression patterns, will enablethe formulation and testing of hypotheses on the molecular genetic changesunderlying ovule diversification. To facilitate future studies on ovule diversification, we will also isolateATS, a gene required for developmental separation of outer and innerinteguments in Arabidopsis. Completion of the proposed work will provide insights into the regulationof plant development, ovule diversification, and their interrelationship.