Tracking the Evolutionary History of Development Genes: Implications for the Diversification of Fruits and Flowers in the Brassicaceae and Cleomaceae

Abstract

Flowers of Brassicaceae are remarkably similar across all species, whereas their fruits vary in almost all conceivable traits, particularly in the tribe Brassiceae. In contrast, Brassicaceae’s sister family, Cleomaceae, exhibits substantial variation in flowers but are more uniform in their fruits. These diversifications represent either variation in pollen transfer or seed dispersal, which are important reproductive traits that likely affect survival. The history of both families involves four shared polyploidy events as well as each independently experiencing separate additional polyploid events. Thus, these families offer an excellent opportunity to investigate whether additional genetic materials from polyploid events are correlated with the evolution of novel flower and fruit morphologies. Based on knowledge from model plants, FRUITFULL (FUL), a fruit development gene important for dehiscence (fruit opening), and TEOSINTE BRANCHED 1/ CYCLOIDEA/ PROLIFERATING CELL FACTOR 1 (TCP1), a gene known to affect floral symmetry, were chosen as candidate genes to examine the evolutionary history and retention of gene duplicates alongside morphological novelty in Brassicaceae and Cleomaceae. A gene phylogeny of FUL was generated to determine if fruit diversity in the tribe Brassiceae (Brassicaceae) could be correlated with FUL copy number, structure, or evolutionary history. Similarly, TCP1 was assessed to identify differences in gene evolutionary history between the florally diverse Cleomaceae and the florally uniform Brassicaceae. Both FUL and TCP1 were found to exhibit complex evolutionary histories, with multiple copies of these genes found in both taxa with and without morphological novelty. However, evaluation of which copies were retained and the rates of selection acting on these genes suggest their involvement in generating morphological diversity of reproductive structures. This thesis presents a strong correlative framework to direct future hypothesis testing using gene expression and functional approaches to further unravel the genetic changes underlying flower and fruit diversification.