The evolutionary relationships amongst species in the order Brassicales (which includes approximately 4550 species, the model plant species Arabidopsis thaliana, and many economically important crop species), are currently poorly known. Knowledge of these relationships is required to interpret the wealth of genomic, developmental, and physiological data available for this group within an evolutionary context. This study will resolve the phylogenetic relationships within the order Brassicales utilizing hundreds of loci encoded across the nuclear, mitochondrial, and chloroplast genomes. In addition, this project will investigate diversification rates and the evolution of each genome compartment (i.e. nuclear and organellar genomes) -- including genome size, gene content (e.g. gene loss and duplications, novel gene functions), and genome structure.
Cultivated and wild Brassicales species possess numerous novel traits and chemistries with enormous value to crop improvement, including biotic resistances (e.g. insects, fungi, and nematodes) and abiotic stress tolerances (e.g. drought, freezing, and heavy metals). In addition, this plant group shares novel chemistries that are beneficial to human health, including treatments for cardiovascular disease and high blood pressure. This research will enhance our understanding of which species share these beneficial novel biochemistries and traits, and characterizing the underlying biosynthetic pathways. Ultimately, this framework will allow these traits to be targeted for pharmaceuticals and to improve crops.
Ancient whole genome duplications are ubiquitous throughout the evolutionary history of higher eukaryotic lineages. These events have been hypothesized to be the basis for major evolutionary transitions, including the origin of novel traits in large species radiations across plants, mushrooms, and animals. Repeated rounds of whole genome duplications, or polyploid events, have been best documented among the flowering plants. We analyzed the impact of the two most recent whole genome duplications in Arabidopsis (a model plant in the mustard family) on speciation rates and the origin of novel traits. Phylogenetic analyses of these two whole genome duplications show that both events occurred following mass extinction events. The origin of two novel classes of chemical defenses (indole and met-derived glucosinolates, which are mustard oils that give wasabi and mustards their unique bitter flavors) are associated with duplicated regulatory and biosynthetic pathways that arose via ancient polyploidy events. Our analyses suggest that the origin of these novel defense compounds spurred an evolutionary arms-race with insect herbivores, such as cabbage butterflies, resulting in massive co-radiations of both the host plant and predatory insects. During the course of our investigations, we developed new methods for analyzing hundreds to thousands of nuclear genes derived from RNA (instead of DNA) to resolve the evolutionary relationships (phylogeny) of species in the order Brassicales (mustards, capers, papaya). In addition to training graduate and undergraduate students at the University of Missouri, this project trained people visiting from other universities. For public outreach, we developed and organized a three-week science project based learning (PBL) module at Lewis and Clark Middle School, included four classrooms of 7th graders (over 100 students), and involved learning the basics of plant genetics and performing multiple independent experiments utilizing the plant model Brassica rapa. The results of our research were presented at research findings at several international conferences (Plant and Animal Genome Conference, International Botanical Conference, and Botany meeting), local meetings at the University of Missouri, and at the Missouri State Capital in front of an audience of state politicians.
