The Development and Evolution of Floral Symmetry in the Zingiberales and Interactive Tools for Teaching Evolution (ArborEd)
Riva Anne Bruenn
Doctor of Philosophy in Plant Biology
University of California, Berkeley
Professor Chelsea D. Specht, Chair
Floral symmetry is a key innovation in the evolution of flowering plants. Zygomorphy, or single-planed symmetry, is associated with the diversification of many flowering plant lineages. The model system for floral symmetry is the snapdragon (Antirrhinum majus). In A. majus flowers, a set of TCP and MYB-related transcription factors form a core gene regulatory network necessary for zygomorphy. The genes involved in this network have been implicated in several independent transitions to zygomorphy from actinomorphy (many-planed symmetry). Although the TCP components of the symmetry network have been investigated across flowering plants, MYB-related transcription factors remain largely unstudied outside of the Asterid group containing A. majus and close relatives. Here we investigate the evolution of MYB-related genes DIVARICATA-like (DIV-like), RADIALIS-like (RAD-like), and DIVARICATA and RADIALIS INTERACTING FACTOR-like (DRIF-like) across flowering plants, and their expression patterns in the developing flowers of two zygomorphic species of the monocot order Zingiberales.
We found that RAD-like and DIV-like are sister MYB-related genes which diverged before the diversification of flowering plants. Each gene contains one MYB-like domain that has been closely conserved throughout flowering plant evolution. Furthermore, we identified candidate homologs to A. majus RAD and DIV in several monocot taxa, with at least three copies of each in the Zingiberales.
In the Zingiberales, RAD-like and DIV-like genes are expressed in Costus spicatus (Costaceae) and Musa basjoo (Musaceae) in patterns consistent with roles in floral symmetry. Using Reverse Transcription PCR and in situ hybridization we recovered asymmetric expression patterns for some RAD-like genes across the dorsal/ventral plane of developing flowers, and universal expression of DIV-like genes, consistent with the model known from Antirrhinum majus.
We identified DRIF-like genes across flowering plants, recovering a previously undescribed duplication in eudicot DRIF Group 1 genes. Furthermore, we recovered candidate DRIF-like genes in Musa basjoo (Musaceae: Zingiberales) with expression patterns similar to those described in A. majus DRIF1 and DRIF2.
Finally, we developed a tutorial for high school and college students to investigate a coevolutionary hypothesis in sharpshooters and their bacterial endosymbionts. This tool will help students understand how comparative evolutionary research is performed, and give them hands-on experience performing common analyses.