Molecular Systematics of the Nymphaeales

植物进化中的一个重要问题涉及开花植物的起源。威斯康星大学密尔沃基分校的唐纳德·莱斯和查尔斯·温佩博士将重点研究睡莲属十个属的原始水生植物之间的系统发育关系，从而研究这个问题。因为这些植物具有被认为是原始的特征，它们可能代表着进化路线上的一个早期“分支”，通向开花植物的其余部分。然而，生物学家一直无法确定睡莲类群与其他植物的确切关系，因为该类群的年龄很长，导致许多形态特征存在相当大的差异。因此，随着时间的推移，许多特征要么丢失，要么改变，阻碍了对系统发育亲缘关系的有意义的估计。在基因水平上，植物的DNA序列记录了它们的进化历史，因为当它们与其他植物分化(通过突变)时，分子变化在相关谱系中变得固定。与形态特征不同，基因可能会在结构上发生变化，但很少会丢失。因此，一个基因的结构可以在看起来形态不同的非常遥远的亲缘关系的群体之间进行比较。利用现代分子生物学技术，莱斯和温佩博士将通过对DNA分子本身的核苷酸进行“排序”来检验这种分子进化变化的记录。他们选择对一种名为“rbcL”的基因进行测序，该基因编码植物中一种重要的光合作用酶的一部分。利用包括聚合酶链式反应在内的最新创新，他们将检查所有10个睡莲属和几个假定相关的类群的DNA序列。通过对序列数据的计算机分析，他们将根据分类群分化时发生的分子变化的谱系，重建这些属之间的系统发育或分支模式。这项工作将阐明原始开花植物之间的进化关系，也可能为更好地了解开花植物的祖先，从而更好地了解其起源提供帮助。

An important issue in plant evolution involves the origin of the flowering plants. Drs. Donald Les and Charles Wimpee of the University of Wisconsin at Milwaukee will study this problem by focusing on phylogenetic relationships among primitive aquatic plants in the waterlily group, the ten genera of the Nymphaeales. Because these plants possess features that are considered primitive, they may represent an early "branch" off the evolutionary line leading to the remainder of the flowering plants. Biologists, however, have been unable to specify the precise relationships of waterlily taxa to other plants because the great age of the group has resulted in considerable divergence in many morphological traits. As a result, the many traits either lost or changed over time have prevented meaningful estimations of phylogenetic affinity. At the gene level, the DNA sequence of plants records their evolutionary history as molecular changes become fixed within related lineages as they diverge (through mutation) from others. Unlike morphological features, genes may change in their structure but are seldom lost. As a result, the structure of one gene can be compared between very distantly related groups that may appear morphologically dissimilar. Using techniques of modern molecular biology, Drs. Les and Wimpee will examine this record of molecular evolutionary change by "sequencing" the nucleotides of the DNA molecule itself. They have chosen to sequence a gene called "rbcl" which codes for a portion of an important enzyme of photosynthesis in plants. Using recent innovations including the polymerase chain reaction, they will examine DNA sequences in all ten waterlily genera and in several putatively related groups. By computer analysis of the sequence data, they will reconstruct the phylogenetic or branching pattern among these genera, based upon the genealogy of molecular changes that have occurred as the taxa diverged. This work will clarify the evolutionary relationships among primitive flowering plants, and it may also provide better understanding of the ancestors, and hence origin, of flowering plants.