Erysimum cheiranthoides, an ecological research system with potential as a genetic and genomic model for studying cardiac glycoside biosynthesis

At least twelve plant families contain species that synthesize cardiac glycosides as defense against herbivory. These inhibitors of animal Na⁺, K⁺-ATPases also have medical uses in treating congestive heart failure and other diseases. However, despite extensive ecological research and centuries of use in both traditional and modern medicine, the complete cardiac glycoside biosynthesis pathway has yet to be elucidated in any plant species. To a large extent, this research deficit results from the fact that cardiac glycosides are produced exclusively by non-model plant species such as Digitalis that have not been amenable to the development of mutagenesis, cloning, and genetic mapping approaches. Recent advances in genome sequencing, transcript profiling, plant transformation, transient expression assays, and plant metabolite analysis have provided new opportunities for the investigation and elucidation of cardiac glycoside biosynthesis pathways. The genetic tools that have been developed for Brassicaceae, in particular Arabidopsis thaliana, may be directly applicable to Erysimum, a Brassicaceae genus that characteristically produces cardiac glycosides as defensive metabolites. We propose that Erysimum cheiranthoides (wormseed wallflower), a rapid-cycling, self-pollinating species with a relatively small, diploid genome, would be a suitable model system to advance research on the biosynthesis of cardiac glycosides in plants.