The Origins of Mustard Oils: Comparative Genomics and Transcriptomics of the Brassicales

Ancient whole genome duplications (WGDs) are ubiquitous throughout the evolutionary history of eukaryotes and have been hypothesized to be the basis for major evolutionary transitions. Repeated rounds of WGDs, or polyploid events, have been best documented among plants; however, the mechanism driving diversification remains poorly understood. We analyzed the impact of the two most recent WGDs in Arabidopsis on diversification rates and the origin of novel phenotypes. We found that both WGD events occurred following mass extinctions and are associated with the origin of chemical defenses (glucosinolates or mustard oils) which spurred an evolutionary arms-race with insect herbivores, resulting in massive co-radiations of both the host plant and predatory insects.  The Brassicales Map Alignment Project (BMAP) and ongoing sequencing of hundreds of accessions of Brassica species, will facilitate the ongoing integration of comparative genomics, population genomics and systems biology.  These integrated studies are a precursor to understanding phenotype evolution and synthetic biology.