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.
